# Simple guide to using a DMM for measurements



## HKJ

[SIZE=+3]Measurement on Flashlight[/SIZE]

Sometimes it can be necessary to do some measurement on a flashlight or battery, this article shows how to do the most common electrical measurements. These measurements are possible on most lights, but not on all.
For some of these measurements I will use two multimeters, a very cheap on and a expensive one.







The expensive meter is a Fluke 189, it has lots of digits, autorange and a very high accuracy.






The cheap one is a "Best DT9205A" from DealExtreme, it has a maximum reading of 1999, range must be selected manually. It is usable for some measurements.
*Note: Many cheap meters will measure wrong, without giving any warning, when the battery is nearly empty*

I have included the following measurements in this guide:


Current consumption: How to measure the tailcap current. 
Current consumption, using resistor: As above, but using a resistor instead of A range om meter. 
Current consumption: How to measure the tailcap current for high current draw lights. 
Power consumption: How to measure the power consumption. 
Tailcap switch: How to check a tailcap switch. 
Battery: How to check a battery. 
Battery tester: Using a battery tester. 
Testing an Incandescent Bulb: How to test a incandescent bulb. 
Testing an led: How to test if a led works and polarity. 
Low ohmic measurement: How to measure small resistances. 
Charge current: How to measure charge current in a charger. 
Charge voltage: How to measure charge voltage in a charger. 


In other articles/guides:

Measuring internal impedance/resistance of a battery 
Building a high current adapter (20A) with low voltage drop. 




[SIZE=+2]Current consumption[/SIZE]

The current consumption can be used to estimate battery lifetime and power usage, it can also tell something about the driver in the light.









Select DC current measurement and move the plugs to the 10A/20A input terminal. For flashlight measurement it is best to select the highest current range, i.e. 10A or 20A range, this is done to keep the voltage drop in the meter as low as possible. For a multilevel flashlight on the lowest levels it can be necessary to use a more sensitive range, but this is only recommended if the reading can be keep below 1/10 of max. on the selected range. For lights that uses multiple amperes a clamp meter is better (see below).










The tailcap is removed from the flashlight and the meter is substituted for that connection, i.e. one probe pin is placed on the battery and the other probe pin is placed on the battery tube, where there is some bare metal. Placing the probe pin on anodized metal will not work.
As can be seen, the two meters do not agree on the value. That is because the current draw is not really DC, but drawn in very fast pulses, the meters does not sum this the same way. This is only a problem on some flashlights.






Using a oscilloscope and a current probe, it is possible to capture the actual current, it swings from nearly zero to about 2.7A. Letting the scope calculate on the waveform gives a value close to the Fluke meter.
*Note: An oscilloscope is good at showing curves, but not very accurate when measuring*

Current measurement can be used to estimate runtime and to reveal what kind of driver the lights is using, here are some measurement with NiHM batteries: Fully charged batteries: 1.35A, partial charged batteries (60% on ZTS): 1.78A, measured with the Fluke.
The current increases with declining voltage, i.e. the driver tries to keep the light output constant. And with eneloop batteries that has 2000mAh (2Ah) I would expect a runtime between 2/1.35 -> 1.5 hour and 2/1.8 -> 1.1 hour.

To calculate the power draw, the current must be multiplied with the battery voltage, as can be seen below it is about 1.2 volt under load and the light uses two batteries, the power is then (voltage*current): 1.2*2*1.6 -> 3.8 watt. Most of this power goes into the led where about 20% is converted to light, all the remaining power is converted to heat.
Note: See next chapter on how to measure the power, instead of estimating it.

Other types of light
Here are some examples on lights without tailcap.










First example is a twisty, where the battery only makes connection when the light is twisted together. The battery tube is removed and the battery is hold in place with the fingers, the meter is used as a substitute for the battery tube connection and connected between battery minus and threads on the head.










In this example the tube and head is anodized, i.e. it is not possible to get a connection on the threads. It is necessary to make the connection at the same place as the battery tube touches the head, luckily there is enough space between the thread and the battery to get the probe down.



[SIZE=+2]Current consumption, using resistor[/SIZE]
Instead of using the A range on the meter, it is possible to use a resistor and measuring the voltage accross the resistor. This has some advantages and some disadvantages:
Advantage: Very good control with series resistance.
Advantage: It is simple to add a filter (Not shown here).
Disadvantage: Result must be calculated.
Disadvantage: Precision is depend on both meter and resistor.
Disadvantage: Wirewound resistor might add some inductance (This is usual not a problem).
When working with development it is also possible to solder all connections, to get better control with contact resistance.









On the meter the most sensitive DC voltage range must be selected (This depends on the resistor, but using a resistor that requires any other range it not a good idea).






The meter must be connected to a low ohmic resistor. This connection is not carrying any current and getting connection with ow contact resistance or low cable resistance from the resistor to the meter is not critical. 
The meter connection and the connection to the flashlight must not be stacked, but must both be connected directly to the resistor leads.
A 0.1 ohm resistor can be used, but a smaller value is better. The resistor must be able to carry at least the current that the flashlight uses. The power rating must also be large enough (any power resistor will usual be large enough, measuring 3 ampere only requires 0.1 ohm 1 watt).






Here I am using the leads on the resistor as connection to get as low resistance as possible. I could have soldered a (short) heavy gauge wire on the leds to get longer leads for connection, but it is not necessary here.
I measure 196 milli volt -> 0.196 volt, the resistor is 0.1 ohm and using ohms law I get voltage/resistance -> 0.196 / 0.1 -> 1.96 ampere. At the same time I know the voltage loss due to the resistor is at least 0.196 volt.

For measuring smaller currents a larger resistor can be used. A good selection of resistors for current measurements would be: 0.047 ohm, 0.47 ohm, 4.7 ohm. That would cover the range from below 5 mA to 4A with a voltage drop below 0.2 volt.

Notes
It is possible to make a low ohmic resistor from a piece of copper wire, but the value will change with temperature (Resistors are made of materials that changes very little with temperatur). Using nickel-chromium resistance wire (Nichrome) is much better and Constantan is best. Use the description in the "Low ohmic measurement" chapter to measure the resistance of the wire.


[SIZE=+2]Current consumption: High current draw[/SIZE]

When the current goes up, the precision on the DMM goes down, this is not because the DMM has a lower precision at high currents, but because the voltage drop over the probes and DMM will have more influence on the measurement. This is because we have to use the full range, not only 10% of the range and even a small resistance in the probes is significant at a couple of amperes when working with low voltage.
One solution is using a small resistor as shown above, another solution is using a current clamp meter.






This picture show some very different clamp meters, what they all have in common is the ability to measure DC current (That is *not* present in all clamp meters).

UNI-T This is the cheapest meters and has a resolution of 10 mA DC. 
Extech A medium quality meter, designed for low current measurement, resolution 1 mA DC. 
Amprobe A more expensive meter, also designed for low current measurement, resolution 1 mA DC. 
Agilent Top of the line meter, resolution 10 mA DC. 

None of the meters are really useful at current below 0.1 A DC, they all work best at multiple amperes. 






Back to flashlights and tailcap measurement, first a measurement with a DMM. This light is bad with 11.6 Ampere in tailcap current, can this be correct?






This looks strange, no current is flowing (wire is not connected) and the meter shows -0.18 Ampere. This is always the case with DC clamp meters, just rotate it a bit and it will change reading, because it changes direction in the Earth magnetic field. A clamp meter measures the magnetic field around the wire, but is also sensitive to other magnetic fields. 





To handle this all DC clamp meters has a zero/rel/null button, press it and the meter shows 0. Remember to keep the meter in the same orientation after pressing the zero button. The meter might need some "warm up" time, before it can keep a stable 0 reading.






Doing the measurement with the clamp meter gives a much lower value, "only" 6.9 ampere. This is because the loss in probes and meter is much lower (The red wire is 2.5 mm2 or 13 AWG). Because this light is stabilized with a buck or boost converter it will draw less current at higher voltages (A direct drive light would draw more current).

Is this value the correct value? I will say it is close, but we do not really know at what voltage, because the batteries will not have the full voltage at 7 ampere current draw. Using the next setup will measure at what voltage the current draw is measured, but requires a more complicated setup and will have the voltage drop in the meter.



[SIZE=+2]Power consumption[/SIZE]

To measure the real power, it is required to measure both current and voltage at the same time. This is best done with two meters, but can also be done with one meter and low ohmic resistor. This description here is for two meters and measures the power to the flashlight, not the power drawn from the battery (The voltmeter must be moved to the battery side of the ammeter for that).
I will start with a drawing to show how the connections are done:





The voltage is measured with the meter closest to the flashlight, this way it is possible to compensate for the voltage drop in the ammeter. The current used by the voltmeter is much to small too affect the current measurement.





The first measurement is without connection to the flashlight, i.e. the current is 0 (Except for a small error on the meter).
The battery has an unloaded voltage of 1.277 volt, i.e. this battery has not recently been charged!
Note: Because the current is 0, the voltage is the correct battery voltage, there is no loss in the ammeter.





With the light connection the voltage is 1.102 volt and the current is 2.126 ampere, i.e. the power is voltage*current -> 1.102*2.126 -> 2.343 watt.
Probably 60% to 70% of this power will reach the led, i.e. around 1.5 watt (The efficiency is rather low, because the voltage has to be boosted to 3 times the input voltage).
Nearly all the power will be converted to heat in the light, except the 20% of the led power that comes out the front as light. That is about 0.3 watt of light.
Note: A fully regulated light will draw close to the same amount of power, independed of the battery voltage, but most 1.5 volt lights are not fully regulated.





Selecting a lower level on the light, will reduce current and battery voltage will go up, both because the battery has higher voltage at lower load and because the voltage drop in the ammeter is smaller.
The result is voltage is 1.263 volt and current is 0.153 ampere, this gives 0.193 watt

Notes
This method requires that the ammeter measures correct, with some meters this can be a problem on some lights (See chapter "Current consumption" above)



[SIZE=+2]Tailcap switch[/SIZE]

It is easy to check if the tailcap works with a multimeter. 









For this measurement the lowest ohm range must be selected. The Fluke with autorange will select the highest ohm range, but will automatic change to the lowest range when measuring.









Before doing any low ohm measurement, it is a good idea to check the meter to see what the lowest value it can show is. The Fluke shows 0.13 and I could have changed that to zero by pressing then "REL" button. The other meter shows 0.6. I.e. anything close to these values can be assumed to be about zero. To get more exact result at these low values, other methods must be used.






One probe pin is placed on the center spring, the other probe pin is placed on the metal connected to the tailcap. The red circle shows the place.









Both meters gives a reading very close to the reading with shorted pins, i.e. the switch/tailcap has a low resistance and is on.









Here the switch is off, or the tailcap/switch is not working correctly.

Some two level lights does have a resistor in the tailcap, this resistance is activated at the low level, expect a resistance in the range 10-100 ohm. A few multi level lights has an electronic tailcap, this makes it impossible to do a valid resistance measurement.



[SIZE=+2]Battery[/SIZE]

The measurements on a battery depends on the chemistry in the battery, I have examples with alkaline and LiIon here.












The DC voltage range must be selected and depending on battery chemistry either the 2V or 20V range must be used. Autoranging meters will select the correct range automatically.









First measurement is on a alkaline battery, this requires the 2V range, it has about 1.4V, but the measurement does not really say anything about how much energy that is left in the battery, only that it still contains some energy. The reason for the difference between the two meters is because I did the following tests, before I measured with the Fluke meter and did not give the battery enough time to recover.









To get a better idea about how it will work in a flashlight, I need a load on the battery, here I am using a 1ohm resistor. The battery still maintains voltage enough to drive a flashlight. The resistor must be at least 3 watt, but a resistor rated for a higher wattage (i.e. 10 watt) is much better, because it will stay cool.









Next battery is a LiIon 18650 battery, this requires the 20V range, the battery has 4.17 volt. For a LiIon this means that it just about fully charged. The voltages for a LiIon must be measured without load and are: Fully charged 4.2V, empty 3.6V
When getting a new LiIon charger it can be a good idea to check the voltage, on the cells, when they are removed from the charger, they must not be above 4.3V, it is much better if they are at 4.2V.



[SIZE=+2]Battery tester[/SIZE]

When measuring batteries, it is much easier with a real battery tester, it has a build in table of the different voltages and chemistries and can use a build in resistor to load the battery when needed.






The ZTS is one of the good battery testers, this model here has support for most of the batteries used in flashlights.









It is very easy to measure all chemistries and get an estimate of remaining power. The meter says 80% for the alkaline and 100% for the LiIon battery.



[SIZE=+2]Testing an Incandescent Bulb[/SIZE]

Usual it is possible to see if a bulb is burned out, but it can also be tested with a multimeter.









For low voltages bulbs the lowest ohm range is fine.









Before doing any low ohm measurement, it is a good idea to check the meter to see what the lowest value it can show is. The Fluke shows 0.13 and I could have changed that to zero by pressing then "REL" button. The other meter shows 0.5. I.e. anything close to these values can be assumed to be about zero. To get more exact result at these low values, other methods must be used.









The probe pins must be place at the two connections on the bulb and they must not touch each other (Can be difficult on the small bulb).

















These bulbs's has a low value and it is difficult to measure exact, one problem is the connection from the probe pin to the bulb, it can be difficult to get a connection with low resistance. Luckily there is no need for exact measurement, as long as the meters show a value, the bulbs works. The measured ohms can not be used to calculate the current in the bulb, when power is connected the temperature will rise more than 2000 degrees and the resistance will increase considerable.









Display for a blown bulb.



[SIZE=+2]Testing an led[/SIZE]

This is a measurement/test not all multimeters can do, some are missing the range and others are not designed for measuring leds. When the meter can do it, this is an easy way to check if a led works and the polarity of the led.









Select the diode range, on some meters this is a shared position on the selection switch and a button must be pressed to select the diode range (On the Fluke I must press the round blue button once).












To test a diode/led the red probe pin must be connected to + and the black probe pin must be connected to -, this is easy when it is marked on the diode mounting plate, but when marking is missing, it is possible to try until the correct connections are found (The meter will not damage the led). The correct connection (i.e. the connection where the led lights up) is the same connection that must be used when mounting the led.









The Fluke meter has no problem testing a led, it shows the voltage over the led and the led is lit. The BEST meter can not show any value, but the test is not completely useless, because the led will glow, when the probe pins are connected correctly.
The voltage shown will depend on the color of the led and the measurement current the meter uses.









There are a lot of possibilities for wrong connections, or defect leds. In the first picture I have connected the probe pins the wrong way around and there is no connection (This is typical for a diode). In the second picture, I have also connected the wrong way around, but this led has a protection diode and there is not an open connection, but instead a low voltage.









Here I have connected the meter to two connected pads and it shows 0 volts and in the last picture I simulate a broken connected.



[SIZE=+2]Low ohmic measurement[/SIZE]
There are many ways to do a low ohmic measurement, the simplest is to buy a 4 terminal ohmmeter, but here I will show how it is done with a voltmeter, a power resistor, a power supply and a little bit of mathematic with ohms law.






Here is the equipment. The power supply must be stabilized supply that can supply between 10 and 15 volt with at least 1.5 ampere. The resistor is a 10 ohm 1% power resistor, I am using a 25 watt resistor (Using a 50 watt would be better).
In the above picture I am measuring the resistance of a piece of blue wire.
To do that I make a circuit from the power supply through the 10 ohm resistor and through the blue wire. 









When I have made the circuit I turn on the power supply and measure the voltage across the 10 ohm resistor and the voltage across the blue wire. When doing these measurement it is very important how I have placed the connection to the power supply and how I have placed the connection to the meter. The measurement probes must not touch the power supply connection.
When I have done the measurements I turn the power supply off again, to avoid heating the resistor.

The measurement I got from the above was:
10 ohm (reference) resistor: 12.067 volt
Blue wire: 0.0077 volt

Now I have to do the following calculation: voltage_over_test_object*reference_resistor/voltage_over_reference_resistor

With numbers: 0.0077*10/12.067 -> 0.0064 ohm or 6.4 mOhm

I.e. the short piece of wire has 6.4 mOhm.









Next up is a tailcap, first picture shows connection to power supply and resistor, in the second picture I have also added the meter probes. Again it is important that the power supply connection and the meter probes do not touch each other, but only touches part of the tailcap.

The measurement I got from the above was:
10 ohm (reference) resistor: 11.92 volt
Tailcap: 0.047 volt

With numbers: 0.047*10/11.92 -> 0.0394 ohm or 34.4 mOhm

I.e. this tailcap has a on resistance of 34 mOhm

Notes





Here is an example how *not* to do it, the measurement probes touches the connection to the power supply. This means that the result will include the connection resistance between the alligator clip and the resistor.

The precision of the above ohmic measurements are very depend on the precision of the 10 ohm resistor and a stable voltage from the power supply, all other errors will mostly cancel each other out.

If I adjust the power supply to deliver exactly 1 ampere, the voltmeter will directly show the resistance in ohms (milli volt is milli ohm) when measuring across the test object, there is no reason to measure across the 10 ohm resistor. 



[SIZE=+2]Charge current[/SIZE]

Not all chargers are completely thruthful with the charge current, with a multimeter it is possible to check the current. There are many possibilities for connecting the meter, I will show one where the battery stays in the charger. This example will be with the WF-139 charger and a LiIon battery, but this methode can be used on most charges, both for LiIon and for NiMH batteries.









First we need some equipment, two pieces of tinfoil, a piece of paper and two alligator clips (Other clips can also be used).
This must be mounted on the charger, together with the battery. This is best done before power is connected to the charger and check that the tinfoil does not touch any metal, except the battery pole and the charger pole, it must *not* touch the nearby charger poles or make a short from the battery + pole to any other metal on the battery. It can be mounted at either the + or the - pole on the charger.






Select DC current measurement and move the plugs to the 10A/20A input terminal. For measurement it is best to select the highest current range, i.e. 10A or 20A range, this is done to keep the voltage drop in the meter as low as possible. For small batteries and low charge current it can be necessary to use a more sensitive range, but this is only recommended if the reading can be keep below 1/10 of max. on the selected range.






Connect the meter to the tinfoil, using the alligator clips to secure the probes. Connecting the probes this way will secure a low impedance and a low voltage drop, i.e. confusing the charger as little as possible.






Here is the final result, with a charge current a bit above 400mA, but not as high as the rating on the charger (it is 450mA). The lower current might be because the battery is nearly full.
Note: Some meters will automatic turn off after some time, this will not interrupt the charge. To make more readings, turn the meter on again.



[SIZE=+2]Charge voltage[/SIZE]

If you want to see how a charger is filling the battery, it might be interesting to measure charge voltage. I will shown an example with WF-134 charge and a LiIon battery, where the battery stays in the charger.









To get access to the poles on the charger two pieces of tinfoil and two alligator clips are used. The tinfoil is placed between the charger poles and the battery poles. This is best done before power is connected to the charger and check that the tinfoil does not touch any metal, except the battery pole and the charger pole, it must *not* touch the nearby charger poles or make a short from the battery pole to any other metal on the battery.






Next the meter must be connect, wrap the tinfoil around the probes and secure with an alligator clip.






Turn the charger on and watch how the battery/charger voltage will rise. With a logging meter or a meter connected to a PC it is possible to record a curve.
Note: LiIon will rise to about 4.2 volt and stay there for some time, before the charge is finished. NiMH will rise to somewhere between 1.5 volt and 1.6 volt and then drop a few milli volt signaling that they are fully charged (This is called dv/dt).



[SIZE=+2]Notes[/SIZE]

















A multimeter needs two connections to measure, one is usual with a red probe and the other with a black probe. By convention the black probe is connected to the COM terminal and the red probe is moved between the other terminals. When connecting the probes to the object to measure, it is not necessary to connect the red probe to + and the black probe to -, either way will do. If the red probe is more negative than the black probe, the display will show a minus sign before the result. The only exception to this is the diode range.


When finished with the meter it is a good idea to *never* leave the probes in the 10A/20A terminals. If the probes are connected to the meter, leave them in the COM and V/OHM terminals.
The reason for this is safety, if someone connects the meter to a mains output, the meter might explode if the probes is in the 10A/20A hole.

Reviews of DMM


----------



## ARA

*Re: Simple guide to measuring on a flashlight*

Thanks mate, thats a gr8 guide for newbies like me. Very easy and detailed


----------



## jayflash

*Re: Simple guide to measuring on a flashlight*

HKJ, have you found that most cheap DMMs are sufficiently accurate when measuring only pure DC & sine wave AC voltage ? That's been my experience. Like you, and unless verified, I wouldn't trust the current measurements of the cheapies.

My Fluke 112 measures only 1.3v from the output on a one AA cell solar pack and the meter is, otherwise, accurate. That's too low, but it was in autorange. I wonder if peak hold would have indicated a voltage closer to the Vf ol the LEDs, had I used that range? I'll have to try that when I retrieve the solar pack from the tree it's in. 

Thanks for your contribution. It's clearly and orderly done, so those new to electrical measurements should find it quite helpful.


----------



## HKJ

*Re: Simple guide to measuring on a flashlight*



jayflash said:


> HKJ, have you found that most cheap DMMs are sufficiently accurate when measuring only pure DC & sine wave AC voltage ? That's been my experience. Like you, and unless verified, I wouldn't trust the current measurements of the cheapies.



I do not really have that much experience with cheap meters, all my other meters are much better than the DX one (and more expensive).



jayflash said:


> My Fluke 112 measures only 1.3v from the output on a one AA cell solar pack and the meter is, otherwise, accurate. That's too low, but it was in autorange. I wonder if peak hold would have indicated a voltage closer to the Vf ol the LEDs, had I used that range? I'll have to try that when I retrieve the solar pack from the tree it's in.



Peak measurement would not have helped, the meter is not putting any load on, when measuring. You must have done something else wrong.


----------



## lrp

*Re: Simple guide to measuring on a flashlight*

Thanks HKJ!! For a newbie like me this is very, very good information!!!


----------



## Curt R

*Re: Simple guide to measuring on a flashlight*

I prefer to measure the voltage drop across a one-tenth ohm 1 % 3 or 5 watt resistor and use ohm's law for current measurements. Most VOMs read DC voltage better than current. 

As for batteries we have found that there is a non visual corrosion build-up on the batteries. We slightly sand the battery ends and have observed a light output of up to 20% in some cases even with brand new batteries. That is one reason we use a Gold plated contact in our flashlights. Do not sand, just wipe with a soft cloth.

Curt


----------



## jayflash

*Re: Simple guide to measuring on a flashlight*



HKJ
Peak measurement would not have helped said:


> The 1.3 volts were measured with the lights (load) on, so I'm guessing there's a brief peak reaching the LED's Vf and the meter is displaying the average measurement. Does that sound correct?


----------



## HKJ

*Re: Simple guide to measuring on a flashlight*



jayflash said:


> The 1.3 volts were measured with the lights (load) on, so I'm guessing there's a brief peak reaching the LED's Vf and the meter is displaying the average measurement. Does that sound correct?



That is a possibility. Can you meter measure AC, ignoring any DC (This can be simulated by connecting a capacitor in series with the meter)? If yes, try doing an AC measurement and see what you get.


----------



## Tekno_Cowboy

*Re: Simple guide to measuring on a flashlight*

A nice, informative guide. It would help quite a few new (and not so new) people troubleshoot problems they might be having. 

Perhaps "sticky" status or similar would be warranted?


----------



## cue003

*Re: Simple guide to measuring on a flashlight*

excellent contribution and great information. Thank you very much.


----------



## Bullzeyebill

*Re: Simple guide to measuring on a flashlight*

I am looking for a bettery measurement of voltage in the 20 or 40 volt range. My inexpensive Cen-Tec p37772 for example, will give a reading for an AA Hybride of 1.296 using the 2 volt scale, and 1.29 on the 20 volt scale, not terribly off, but not too accurate in the 20 volt scale. The Cen-Tex is using 3 1/2 digits.

My question, I guess, is do I need the expensive Fluke 189 to get a three decimal reading for the 20 volts scale (or 40 volt scale on some models). I am more interested in readings for Lithium Ion cells, and more accuracy.

Would you demonstrate another DMM, a Fluke, not as expensive, as an example for the answer to my question?

Bill

Bill


----------



## HKJ

*Re: Simple guide to measuring on a flashlight*



Bullzeyebill said:


> I am looking for a bettery measurement of voltage in the 20 or 40 volt range. My inexpensive Cen-Tec p37772 for example, will give a reading for an AA Hybride of 1.296 using the 2 volt scale, and 1.29 on the 20 volt scale, not terribly off, but not too accurate in the 20 volt scale. The Cen-Tex is using 3 1/2 digits.
> 
> My question, I guess, is do I need the expensive Fluke 189 to get a three decimal reading for the 20 volts scale (or 40 volt scale on some models). I am more interested in readings for Lithium Ion cells, and more accuracy.
> 
> Would you demonstrate another DMM, a Fluke, not as expensive, as an example for the answer to my question?



I would say that 1.296 and 1.29 shows some very good tracking between the ranges. Most meters has a tolerance of +/-2 on the last digits for the DC voltage range, on top of that you must add the meters tolerance of +/- x% (Depending on meter x is between 0.5 and 0.025).

For LiIon you do not need a better readout than 4.21. 
With a 0.5% +/-2 meter this means that the voltage is between 4.169 and 4.251 volt.
With a 0.1% +/-2 meter this means that the voltage is between 4.186 and 4.234 volt.

To get more digits you can look for meters with a max. of 3999, 4999 or 5999, instead of 1999. But remember to look at the accuracy specification too.
A 4.210 reading with a 0.1% +/-2 meter means that the voltage is between 4.204 and 4.216 volt.


----------



## jayflash

*Re: Simple guide to measuring on a flashlight*



HKJ said:


> That is a possibility. Can you meter measure AC, ignoring any DC (This can be simulated by connecting a capacitor in series with the meter)? If yes, try doing an AC measurement and see what you get.



I should have mentioned that I also tried the AC range, but no, it did not indicate any voltage. It's time to get a new, small, 'scope, anyway. Would you believe my old one uses tubes and it isn't working. (old toys for old guys) I'm not sure I want to put much time into the old beast and it's gotta stay on the bench -- can't lug 20 pounds of fragile glassware around.


----------



## ElectronGuru

*Re: Simple guide to measuring on a flashlight*

Outstanding, thank you for putting this together!

:kewlpics:


----------



## HKJ

*Re: Simple guide to measuring on a flashlight*



jayflash said:


> I should have mentioned that I also tried the AC range, but no, it did not indicate any voltage. It's time to get a new, small, 'scope, anyway. Would you believe my old one uses tubes and it isn't working. (old toys for old guys) I'm not sure I want to put much time into the old beast and it's gotta stay on the bench -- can't lug 20 pounds of fragile glassware around.



In that case I do not believe that there are any pulses on it (or they are to short for the meter to measure).

A cheap scope to get is a small PicoScope together with a PC and it works very well (You can see many traces from a pico scope on my website).


----------



## Linger

*Re: Simple guide to measuring on a flashlight*

I've been searching for this since I got my DMM (2mo ago), over and again b/c I knew i'd crossed these items in different threads.
Obviously I hadn't found it, b/c it wasn't written yet. Thanx HKJ!lovecpf


----------



## koala

*Re: Simple guide to measuring on a flashlight*

HKJ, excellent guide. Good lighting in your photography.


----------



## slate

*Re: Simple guide to measuring on a flashlight*

Thanks for the excellent review/article. I have a question. Is there anything out there similar to the ZTS model that does not cost as much. It looks like the ZTS model is $70. I prefer the simplicity of the ZTS but not the price tag. Looks like the BEST meter pictured is only $14 from DX

Thanks


----------



## HKJ

*Re: Simple guide to measuring on a flashlight*



slate said:


> Thanks for the excellent review/article. I have a question. Is there anything out there similar to the ZTS model that does not cost as much. It looks like the ZTS model is $70. I prefer the simplicity of the ZTS but not the price tag. Looks like the BEST meter pictured is only $14 from DX
> 
> Thanks



ZTS has cheaper models (Mini-MBT), and you can also get other battery tester, but they are mostly for alkaline.

The BEST meter is very cheap. I bought it just to see what it was and do not plan on using it for any serious measurements (but that is because I already have much better meters). I believe that it is fine for checking batteries, tailcaps and other things around the house. But if the readout show something strange, I would recommend trying a new battery in the meter or another (cheap) meter.


----------



## DM51

*Re: Simple guide to measuring on a flashlight*

This is a very good illustrated guide, which I am sure many members will find useful. I have added it to the "Threads of Interest" sticky here.


----------



## HKJ

I have added a few more measurements and some notes to the guide.


----------



## Mr Happy

Looking at the comparative readings with the Fluke meter, that BEST meter seems to be quite accurate. Many will wonder if that degree of accuracy from cheaper meters is typical, or if it is a "fluke"?


----------



## HKJ

Mr Happy said:


> Looking at the comparative readings with the Fluke meter, that BEST meter seems to be quite accurate. Many will wonder if that degree of accuracy from cheaper meters is typical, or if it is a "fluke"?



I do not have much experience with cheap meters, but as far as I know they usual are quite accurate, except when they are not (Like when the battery is low or measuring on a "strange" waveform).
The cheap meters are also much more exposed to damage from misuse. the Fluke meter can basically not be damaged from any ordinary voltages, the worst you can do is blowing a fuse in it.


----------



## LuxLuthor

HKJ, it is obvious that you spent a lot of time putting this together with excellent photos, and logical discussions. Keeping it simple is not always easy, but you did it very well.

Thank you for making such a wonderful contribution to the community. :thumbsup:


----------



## VidPro

yup excelent guide and great clear clean pics. 

With such great guide/pics, could you do the Bench power supply too 
(or not, just asking)


----------



## HKJ

VidPro said:


> With such great guide/pics, could you do the Bench power supply too
> (or not, just asking)



I do not really know what kind of guide to make for a bench power supply?

If it is how to connect it to a flashlight for measurement it can be a bit problematic, due to the current draw from some lights (See the oscilloscope curve in my first post), not all power supplies works well with this kind of current draw.


----------



## VidPro

HKJ said:


> I do not really know what kind of guide to make for a bench power supply?
> 
> If it is how to connect it to a flashlight for measurement it can be a bit problematic, due to the current draw from some lights (See the oscilloscope curve in my first post), not all power supplies works well with this kind of current draw.


 
i havent had any problem hooking up flashlight heads to voltage current controlled type bench supplies. probably the readings on my cheap stuff are just averaging, but that is all i need to know.

How the flashlight head (bulb or led or whatever) reacts to different voltages, for the purpose of determining the battery it can handle, if its buck or boost, the regulation, and how long it will last with that battery type, overdrive and all that stuff.
then how to charge various batteries using voltage-current controls.

one could start with the most simple thing, lighting up a LED, and finding out things like VF, smoking a led to test durability, taking a incan bulb over spec to see where it pops at. 

powering charge curcuits , drivers, gadgets, to see thier current draw.

just about anything you did with the Meter, you can do stuff with the bench supply., and lots of that could be done with a <1A supply.


----------



## HKJ

VidPro said:


> i havent had any problem hooking up flashlight heads to voltage current controlled type bench supplies. probably the readings on my cheap stuff are just averaging, but that is all i need to know.
> 
> How the flashlight head (bulb or led or whatever) reacts to different voltages, for the purpose of determining the battery it can handle, if its buck or boost, the regulation, and how long it will last with that battery type, overdrive and all that stuff.
> then how to charge various batteries using voltage-current controls.
> 
> one could start with the most simple thing, lighting up a LED, and finding out things like VF, smoking a led to test durability, taking a incan bulb over spec to see where it pops at.
> 
> powering charge curcuits , drivers, gadgets, to see thier current draw.
> 
> just about anything you did with the Meter, you can do stuff with the bench supply., and lots of that could be done with a <1A supply.



I got you idea and it could be interesting to do that kind of guide, but it will have to include not only "how to", but also something about what to do with the measurements. I.e. if a led is measured to have a Vf of 3.2 volt, what practical implication does that have (One is that a boost regulator and LiIon would be a bad idea).

I am using a 0-15V 3A supply for testing flashlights, where I have replaced the voltage potmeter with a 10 turn potmeter. That is a big improvement and I might also do it on some of my other power supplies.

I do not have time to do it in the next couple of weeks, but maybe later.


----------



## VidPro

yes it would be more "text" based , but with pictures 
pictures in a post tell SOOO much, and make things look a lot simpler, like what you have here qualifies as "Worth a Thousand Words":thumbsup:


----------



## hazna

thanks for the guide, I'm a complete newbie to DMM...

Could you also explain how to measure the charging rate from a charger with the DMM? Thanks


----------



## HKJ

hazna said:


> Could you also explain how to measure the charging rate from a charger with the DMM? Thanks



Ok, it is added to the guide.


----------



## hazna

thanks for the update, HKJ! :twothumbs

Got a question though, in regards to measuring the output from a charger... why do you put both the metal foil pieces on the positive end? (thought you would put one on the positive and one on the negative) As mentioned previously, I'm a newbie when it comes to this sort of stuff.


----------



## HKJ

hazna said:


> thanks for the update, HKJ! :twothumbs
> 
> Got a question though, in regards to measuring the output from a charger... why do you put both the metal foil pieces on the positive end? (thought you would put one on the positive and one on the negative) As mentioned previously, I'm a newbie when it comes to this sort of stuff.



When measuring current I need the meter in series with the battery, like this:

Charger----meter----battery------charger

If I had wanted to measure the voltage, I would have to connected the meter to both ends of the battery and use the V/OHM terminal on the meter.


----------



## kosPap

*Re: Simple guide to measuring on a flashlight*



Curt R said:


> I prefer to measure the voltage drop across a one-tenth ohm 1 % 3 or 5 watt resistor and use ohm's law for current measurements. Most VOMs read DC voltage better than current.
> ...snip snip...
> Curt


 
HKJ I am glad you made this guide...sadly i found it after I discovered how to make these measurements by other sources...and by shear luck I made my first current mesurement on a resistor thsi morning!!!

But for the benefit of the Newbees could you add a section on current mesurement with this method? (both pics and calculations)

thumbs up my friend, kostas


----------



## HKJ

*Re: Simple guide to measuring on a flashlight*



kosPap said:


> HKJ I am glad you made this guide...sadly i found it after I discovered how to make these measurements by other sources...and by shear luck I made my first current mesurement on a resistor thsi morning!!!
> 
> But for the benefit of the Newbees could you add a section on current mesurement with this method? (both pics and calculations)
> 
> thumbs up my friend, kostas



It is more complicated to use a resistor and the result might not be any better, it might be worse, but that depends on a lot of factors.

But if it is wanted, I can add it.


----------



## karlthev

I just saw this...great thread and job on this!! Thanks.


Karl


----------



## nfetterly

Wow - thank you for the superb effort here. Wonderfully illustrated! I know that I can make use of this - I've only been using my (cheap) meter for very basic stuff, not as much troubleshooting as I will be able to now.

Neale


----------



## mbiraman

Great job HKJ. I was wondering . On the ZTS battery tester under 3.6v you see listed a number of batteries but not 14500. My aw 14500's are 3.7. Does it matter ?? . Can the 14500's be tested in the 3.6 spot??


----------



## HKJ

mbiraman said:


> Great job HKJ. I was wondering . On the ZTS battery tester under 3.6v you see listed a number of batteries but not 14500. My aw 14500's are 3.7. Does it matter ?? . Can the 14500's be tested in the 3.6 spot??



Yes, it can, it is about the same as RCR123A/16340.


----------



## mbiraman

HKJ said:


> Yes, it can, it is about the same as RCR123A/16340.



Thanks HKJ


----------



## hazna

I just got my cheap DMM from DX. Having a few troubles in in measuring the voltage now. When I first got it, I was able to measure the voltage on lithium-ion cells. However after running some tests with on a charger (to measure the current from it), I can't seem to measure voltage anymore. I can still measure current though. Did I fry something when measuring the current on charger? I actually left the DMM attached to the charger, while it was charging.


----------



## VidPro

hazna said:


> However after running some tests with on a charger (to measure the current from it), I can't seem to measure voltage anymore. I can still measure current though. .



the small side of most DMMs is usually fused, with a easily replaceable fuse. the High Amps side is often not fused, because it would add in to much resistance.
the small side is for doing voltage, and lower amps and all, and will pop the fast acting fuse anytime you jam to much power into it to protect the small side from total aniliation.
so did you check the fuse?


----------



## hazna

Well I opened up the DMM to look for the fuse, after jiggling a few things around (namely the bit that connects to the battery), seems to be working again!


----------



## Billy Berue

Thanks for this, very very helpful. A couple quick questions.

1. Can you safely measure voltage of Li-Ion cells while they are charging? If so, is it as simple as touching the probes to each terminal while it's in the charging bay? Or is this a recipe for some sort of disaster? Would doing so provide you with the voltage of the cell, or would it simply be measuring the voltage of the charging current?

2. Is it possible to measure the voltage of a Li-Ion cell while in actual use in the flashlight? I have successfully used the tailcap method to measure current while in use, but just curious if there was a way to measure the actual voltage. I am aware that you can use a resistor to simulate the load of the specific flashlight, but I am curious if the voltage can be measured more directly.

3. How do you measure Vf and If in a regulated light?


Thanks again, and sorry for all the questions. I usually like to ask questions before playing with electricity.


----------



## HKJ

Billy Berue said:


> Thanks for this, very very helpful. A couple quick questions.
> 
> 1. Can you safely measure voltage of Li-Ion cells while they are charging? If so, is it as simple as touching the probes to each terminal while it's in the charging bay? Or is this a recipe for some sort of disaster? Would doing so provide you with the voltage of the cell, or would it simply be measuring the voltage of the charging current?



While charging the voltage on the LiIon is higher than the usual no load voltage and how much higher depends on the charge current. I.e. you can not use it to see when it is completely charged.




Billy Berue said:


> 2. Is it possible to measure the voltage of a Li-Ion cell while in actual use in the flashlight? I have successfully used the tailcap method to measure current while in use, but just curious if there was a way to measure the actual voltage. I am aware that you can use a resistor to simulate the load of the specific flashlight, but I am curious if the voltage can be measured more directly.



To measure the voltage you need a probe on each end of the battery, the easy way to do that would be to take the battery out of the flashlight and then run wires into the light from the battery. 



Billy Berue said:


> 3. How do you measure Vf and If in a regulated light?



Both requires access to the led. 

Vf is easy to measure, you put the meter on volt and connect it to the same place as the wires from the driver is connected to the led. *BUT* shorting the probes to the flashlight tube or to the some metal part in the light might blow the driver in the light.

If requires to unsolder one of the wires to the led and connect it to the A terminal on the meter, the COM terminal must be connected to the place where the wire was soldered in. Again the risk of damaging the driver is high.

Also note that opening the light probably will reduce the cooling of the led, i.e. be careful not to cook the led.


----------



## Billy Berue

HKJ said:


> While charging the voltage on the LiIon is higher than the usual no load voltage and how much higher depends on the charge current. I.e. you can not use it to see when it is completely charged.



Thanks, HKJ. I have measured the charging current of my WF-139 using the aluminum foil method in your guide. Is the voltage difference between a Li-Ion cell while charging versus resting typically constant (given a constant charging current)? I suppose I could determine this for myself with some experimentation, but I thought I'd ask anyway. If the difference is constant at a given charging current, then I should be able to monitor the voltage while charging to determine when to pull the cells off the charger. Is there a formula or something that can be used to mathematically determine what that difference should be?

If none of that is possible or practical, then I suppose I could use some trial and error to determine the voltage while charging at the point that the cells reach 4.2v (as measured once taken off the charger) to determine when they should be pulled from the charger.

Looks like my question is drifting a bit from the main topic, so I'll try to refrain from any more follow-ups in this thread, but will start a new thread if needed.


----------



## HKJ

Billy Berue said:


> Thanks, HKJ. I have measured the charging current of my WF-139 using the aluminum foil method in your guide. Is the voltage difference between a Li-Ion cell while charging versus resting typically constant (given a constant charging current)? I suppose I could determine this for myself with some experimentation, but I thought I'd ask anyway. If the difference is constant at a given charging current, then I should be able to monitor the voltage while charging to determine when to pull the cells off the charger. Is there a formula or something that can be used to mathematically determine what that difference should be?
> 
> If none of that is possible or practical, then I suppose I could use some trial and error to determine the voltage while charging at the point that the cells reach 4.2v (as measured once taken off the charger) to determine when they should be pulled from the charger.



I have a few comments to this: LiIon are not finished with charging when they reach 4.2 volt, they need to stay some time at the voltage before they are full. 
But the WF-139 does not use the standard charge algorithm, I believe that it keeps the charge current up, until the batteries reaches 4.2 volt without current (It does turn charge current off at regular intervals to measure the voltage). This way to charge is faster than standard, but might be a bit harder on the batteries.

And as long as AW recommends the WF139 charge I have no problems with using it for my LiIon batteries.

You could probably make a table with the voltage measured during charge and the charge %, but that table would only be valid for one type and manufacturer of batteries.


----------



## Billy Berue

HKJ, I have another question, this time regarding the measurement of current draw. I understand the fairly straightforward tailcap method you described above:



HKJ said:


> The tailcap is removed from the flashlight and the meter is substituted for that connection, i.e. one probe pin is placed on the battery and the other probe pin is placed on the battery tube, where there is some bare metal. Placing the probe pin on anodized metal will not work.



But I was reading another of your posts in wattnot's review of the Fenix TK40 over on the Flashlight Reviews forum, where you described what appears to be another method of measuring current draw:



HKJ said:


> ...I open the light between the head and the tube. This makes it easy to make the connection for current measurement: One alligator clip wire between tube and head, one alligator clip wire between outer rings and the meter between the center positions.



I can't seem to quite visualize what you are saying here. If not too much trouble, I'd love to see a photo of the setup for that technique. 

In fact, in a subsequent post further down in the TK40 review thread, you actually show a photo of what seems to be a similar technique that you were using to measure the alleged "parasitic drain" of the TK40. But in that setup, the head appears to be connected directly to the battery, and the body tube and tailcap appear to be uninvolved in the circuit. I assume that what is being shown in that photo is not the same technique that I quoted above for measuring current draw of the light while it is actually running.

Hope that makes sense. And thanks in advance for your help.


----------



## HKJ

Billy Berue said:


> I can't seem to quite visualize what you are saying here. If not too much trouble, I'd love to see a photo of the setup for that technique.
> 
> In fact, in a subsequent post further down in the TK40 review thread, you actually show a photo of what seems to be a similar technique that you were using to measure the alleged "parasitic drain" of the TK40. But in that setup, the head appears to be connected directly to the battery, and the body tube and tailcap appear to be uninvolved in the circuit. I assume that what is being shown in that photo is not the same technique that I quoted above for measuring current draw of the light while it is actually running.



In the photo where I measure the standby drain, I do not need to switch the light on, that is the reason that I can do without the body tube and switch.
To enable use of the switch, I must put the battery container into the body tube and also make a connection between the threads on the body tube and the treads on the head.
Or I could make a momentary short between the outer ring in the head and the threads in the head, that would simulate a press on the switch (A flat screwdriver is very useful for that).

Also remember to use the 10A/20A terminal on the meter to measure current drain with the light on!

Here is the photo with the standby current measurement, just add a flat screwdriver between outer ring and threads, when it is touching both the ring and the threads, it simulates pressed switch:


----------



## Billy Berue

HKJ said:


> Or I could make a momentary short between the outer ring in the head and the threads in the head, that would simulate a press on the switch (A flat screwdriver is very useful for that)....
> 
> Here is the photo with the standby current measurement, just add a flat screwdriver between outer ring and threads, when it is touching both the ring and the threads, it simulates pressed switch:


Excellent...thanks, HKJ. I will try this when I get home tonight from work. Just to make sure I understand, when you say "momentary short," you simply mean to use the flat screwdriver to touch the inner threads of the head to the outer ring in the head *and then to release the screwdriver after a quick moment* (i.e., just enough for the circuit to register the simulated tailcap click), right? In other words, I'm not supposed to leave the screwdriver in contact with the ring and threads for the duration of the measurement, correct? Sorry to ask questions about what must be so obvious to you. But I really don't want to fry my new TK40. :duh2:


----------



## Justin Case

The difference appears to be due to the fact that the TK40's multimode electronics are all in the head. So that's all you need to power up and probe for parasitic resistance. The battery tube and tailcap are just glorified wires and unnecessary to include in the circuit. A few other systems have the electronics in the tailcap (e.g., the OpticsHQ multifunction tailcap). In that case, you need to insert your DMM in series with the tailcap to measure parasitic current.


----------



## HKJ

Billy Berue said:


> Excellent...thanks, HKJ. I will try this when I get home tonight from work. Just to make sure I understand, when you say "momentary short," you simply mean to use the flat screwdriver to touch the inner threads of the head to the outer ring in the head *and then to release the screwdriver after a quick moment* (i.e., just enough for the circuit to register the simulated tailcap click), right?



That is correct for turning the light on/off, to change brightness you need to short a bit longer (Exactly like you need to hold the switch down longer to change brightness).


----------



## Billy Berue

Again, thanks. Your posts are extremely educational.

Sorry, but one more question.  And I think you addressed this somewhere else, but now I can't find it. Anyway, I suppose the fairly direct connection of the battery to the head imparts very little resistance to the circuit, depending on the quality/gauge of the connecting wires. I believe my DMM applies some internal resistance when measuring current draw, which I guess in theory would introduce a touch of voltage sag. Since the TK40 has constant output, that small voltage sag would cause it to draw a small amount of additional current. I'm guessing this would be small enough so as to have an insignificant effect on the measurements produced by this technique, particularly if you were measuring current draw while the light was powered on. I suppose it might be more significant to the measurement if you were trying to accurately measure "parasitic drain" while the light was powered off, since the current being drawn in that scenario is so low to begin with.

My question is: if you followed the alternative method of measuring current draw (i.e., the method that enables the switch, quoted below from your previous post), would the additional resistance imposed by the tailcap and body tube yield a different measurement of current draw? 



HKJ said:


> To enable use of the switch, I must put the battery container into the body tube and also make a connection between the threads on the body tube and the treads on the head.



I'm guessing that, in theory, it would yield a slightly higher current for a constant power system like the TK40. But, I'm also guessing that the difference in current draw would not be significant unless you were trying to measure parasitic drain.

I'll try to resist from asking any additional questions so as to not wear too thin on your patience.


----------



## HKJ

Billy Berue said:


> My question is: if you followed the alternative method of measuring current draw (i.e., the method that enables the switch, quoted below from your previous post), would the additional resistance imposed by the tailcap and body tube yield a different measurement of current draw?



In this light the switch does not carry any significant current, i.e. you result will be exactly the same, independent on how you connect the switch.

The wires, connection and meter will add a resistance, that translates into a voltage drop and the light will compensate by increasing the current. But the charge state of the batteries will have a much larger effect on the voltage and current drain.

These "tailcap" measurements can never be anything but a *rough* guide to the current consumption in the different modes, a much better way to evaluate the current consumption is making a graph like this:





This graph is *not* for TK40.

But again there are some factors that will spoil precision, both drivers with a slightly unstable current (this is very common) and current changing with the temperature of the led and drive (The temperature depends on how long time the light is on and at what power level).


----------



## Billy Berue

HKJ, all I can say is... :bow:

Really, really appreciate your patience and thorough explanation.


----------



## Billy Berue

HKJ said:


> In [the TK40] the switch does not carry any significant current, i.e. you result will be exactly the same, independent on how you connect the switch.



I'll actually try it both ways for myself later tonight, just as an educational exercise/experiment. The CPF geek in me is really coming out right now.


----------



## ECKO32

After picking up some tips i decided to play with my cheapo dx meter
and do some cceq tests,Thanks so much for the informative guide and the pics really helped take some of the guess work out:twothumbs:twothumbs:twothumbs


----------



## Vikas Sontakke

What is the typical resolution of DMM when measuring resistance?

- Vikas


----------



## Vikas Sontakke

Wow, what a great job HKJ! I don't know how I had missed this.
Fabulous work and thanks for putting such effort in to it.

- Vikas


----------



## HKJ

Vikas Sontakke said:


> What is the typical resolution of DMM when measuring resistance?
> 
> - Vikas



Most meters are 3½ digit, i.e. a 1999 readout, but you have better meters with 3999, 4999 or 5999 readout. They use all the digits to show a ohm value, but the precision is not that good, more like 1% of actual reading.
Meters with two wires can usual not measure with better resolution than 0.1 ohm for low ohmic values and even that is doubtful, as you can see on my pictures. 
If you really want to measure low ohm values you need a 4 terminal meter or do you own 4 terminal measurements. It is easy enough to do 4 terminal measurements, you just need a stabilized power supply and a resistor, then you can get 0.001 ohm resolution without much trouble.


----------



## Zeva

could you please elaborate about how to estimate run time? say i have a flashlight that is drawing 1 amp but i am using 2x RCR 123 or 1x 18650 how would you guess run time? thanks a bunch!


----------



## HKJ

Zeva said:


> could you please elaborate about how to estimate run time? say i have a flashlight that is drawing 1 amp but i am using 2x RCR 123 or 1x 18650 how would you guess run time? thanks a bunch!



You need to measure the current at the tailcap and it will probably not be the same with 2xRCR123 or 1x18650.

The you divide the mAh with the measured current, but if you have the current in amp you need to convert the mAh to Ah first. Luckily it is very easy, just move the point 3 places, i.e. 2400 mAh is 2.4 Ah and will give an estimated runtime of 2.4/1 -> 2.4h hours.
But that is only a rough estimate, one reason is that the mAh specifications on LiIon batteries are usual very optimistic (I have done some measurements on 18650 batteries). Other problems includes meters that can not measured amps correct, due to pulsing current and that current draw will vary between full and empty batteries.


----------



## Zeva

Ohhh isee! one more question..> if my flashlight uses 2x RCR-123 and one RCR-123 is rated at 880 MAH would i double that? or would it be 880 MAH? soo this light is drawing about .6 so i assume thats 880/.6 = 1466.6666? or 2933.333? and i asume thats 1.46 hrs or 2.93 hrs? thanks a bunch !


----------



## HKJ

Zeva said:


> Ohhh isee! one more question..> if my flashlight uses 2x RCR-123 and one RCR-123 is rated at 880 MAH would i double that? or would it be 880 MAH? soo this light is drawing about .6 so i assume thats 880/.6 = 1466.6666? or 2933.333? and i asume thats 1.46 hrs or 2.93 hrs? thanks a bunch !



They will be in series, that gives double the volt and the same mAh, i.e. the calculation would be 0.880/0.6 -> 1.46 
But that result would be very optimistic, the 880 mAh is probably more like 600 mAh, i.e. 1 hour would be more realistic.


----------



## Zeva

Thanks for the info! my DX DM doesnt seem that bad!


----------



## ampdude

I have two less expensive older DMM's of different brands which don't have auto-ranging and they both measure approximately the same, I haven't found any difference between the two. I wouldn't mind owning a Fluke, but I haven't found the need for a more expensive meter.


----------



## kosPap

just want ot ask....

circuit & conection resistance will show up under load. is there a problem measuring it (ie wire from +batt to +board) will the flashlight/circuit is running?


----------



## HKJ

kosPap said:


> just want ot ask....
> 
> circuit & conection resistance will show up under load. is there a problem measuring it (ie wire from +batt to +board) will the flashlight/circuit is running?



Do you want to measure resistance in wires and switches? 
This is a very low resistance and requires a special technique to measure and is not covered in this guide. If there is a need for it I can add it to the guide.


----------



## Mr Happy

Also never use the resistance setting of a multimeter on a live circuit with current flowing through it.


----------



## kosPap

Mr Happy said:


> Also never use the resistance setting of a multimeter on a live circuit with current flowing through it.


 
That was exactly what I thought it would be and made me ask...




HKJ said:


> Do you want to measure resistance in wires and switches?
> This is a very low resistance and requires a special technique to measure and is not covered in this guide. If there is a need for it I can add it to the guide.


 
let me guess ...parallel metering with a know value resistor?


----------



## HKJ

kosPap said:


> let me guess ...parallel metering with a know value resistor?



No, use a known current, measure voltage drop. This way you can measure 0.01 ohm with less than 10% tolerance (in many cases a lot better than that).


----------



## kosPap

right....the skinny imlemation of Ohm law....
thanks


----------



## kosPap

Just a question, even if it turns out to be nonsense...

Can I have a DMM with all 3 leads connected while measuring (Current and Voltage alternatively)

My purpose is to monitor the Li-Ion charger with one DMM only. So if I connect the elads correctly will it matter is for example, current is flowing still through the 10A socket while the Dial is turned to voltage metering?

Thanks, kostas


----------



## HKJ

kosPap said:


> Just a question, even if it turns out to be nonsense...
> 
> Can I have a DMM with all 3 leads connected while measuring (Current and Voltage alternatively)
> 
> My purpose is to monitor the Li-Ion charger with one DMM only. So if I connect the elads correctly will it matter is for example, current is flowing still through the 10A socket while the Dial is turned to voltage metering?
> 
> Thanks, kostas



*NO*, some of the better meters will warn about incorrect probe connection.

With that said, it might work on some meters, but you will have to test it.


----------



## Mr Happy

I think generally it will work (the 10 A socket is just a low resistance shunt internally), but it is risky. If you forget which lead is which and accidentally connect the current probe to the wrong place you will blow the fuse in the meter (if there is one). Also when you turn the dial between voltage and current settings you might pass through other functions like resistance that do not like having a voltage across the probes.


----------



## 45/70

Mr Happy said:


> ......If you forget which lead is which and accidentally connect the current probe to the wrong place you will blow the fuse in the meter.



I just thought I'd point out that most relatively inexpensive DMM's anyway, do not incorporate a fuse in the 10A circuit, only the lessor ranges.

Dave


----------



## HKJ

kosPap said:


> My purpose is to monitor the Li-Ion charger with one DMM only. So if I connect the elads correctly will it matter is for example, current is flowing still through the 10A socket while the Dial is turned to voltage metering?



A safe way to do it is to add a 0.1 ohm resistor in series with the battery, the switch the meter between the resistor and the battery. 
With some chargers you might even be able to fit the resistor inside the charger, add a switch and two wires out to the meter.


----------



## kosPap

hmmm thanks....


----------



## Zero_Enigma

Just found this guide. Thank you OP. I've not checked everything out but being a visual learner the pictures greatly allowed me to learn faster. I can see some questions I had about how to test a light bulb answered there as with how to put the battery under simulted load via resistor so you know if the battery has enough power to drive the LED.

I like the guide so far even thou I just skimmed it. Dropping a comment of thanks and also so I subscribe to this thread to find it later. Found it off a tagline of some other user here. So far it seems like it was geared with the flashaholic/batteriholic which is what I like with many scenrios of testing... I'll check out more later when I have time. :twothumbs DMM newbie here that only uses it just to test batteries. :sigh:


----------



## RAGE CAGE

excellent resource- thank you!


----------



## jmcf1949

An excellent resource for all of us, thank you very much HKJ. One question though. Is there a way to make current draw measurements on a light such as the Malkoff MD2, which has no removable tailcap.

Regards,

Jim - Semper Fi


----------



## HKJ

jmcf1949 said:


> An excellent resource for all of us, thank you very much HKJ. One question though. Is there a way to make current draw measurements on a light such as the Malkoff MD2, which has no removable tailcap.



I do not known how the MD2 is build, but I have added two examples on lights without tailcap. Fell free to ask for other examples on measurements, if I have the time and light I will add it.


----------



## ampdude

45/70 said:


> I just thought I'd point out that most relatively inexpensive DMM's anyway, do not incorporate a fuse in the 10A circuit, only the lessor ranges.
> 
> Dave



Thanks for the tip, I'll have to check that on mine. I've blown fuses before, but it's been a long time. I think it was in the 400mA range and not the 10A one when I've done it most of the time. If I think it might be over 300mA and don't need a hyper-accurate reading I just use the 10A range, but I thought mine were fused at 10A.


----------



## HKJ

ampdude said:


> Thanks for the tip, I'll have to check that on mine. I've blown fuses before, but it's been a long time. I think it was in the 400mA range and not the 10A one when I've done it most of the time. If I think it might be over 300mA and don't need a hyper-accurate reading I just use the 10A range, but I thought mine were fused at 10A.



There is one problem with a 10A range without fuse: if (by accident) the meter with probes in the 10A range is connected directly to main voltage, the meter might explode.

Using the low ampere range can give some measurements errors when working with low voltage (i.e. flashlights), because of voltage drop in the meter.


----------



## aingel2k1

Hello, and thank you for this valuble information!! I have one question however.. on the section where you explian the "power Draw" it states: "To calculate the power draw, the current must be multiplied with the battery voltage, as can be seen below it is about 1.2 volt under load and the light uses two batteries, the power is then (voltage*current): 1.2*2*1.6 -> 3.8 watt. Most of this power goes into the led where about 20% is converted to light, all the remaining power is converted to heat."
but the photo below is of the tailcap measurements. I didnt get the reference to the "1.2v under load"... Are you saying to measure the battery " while in use" ?? and where did you get the "1.6" in the problem? was it, one battery measured 1.2v and the other measured 1.6v?
Thank you!!


----------



## HKJ

aingel2k1 said:


> I have one question however.. on the section where you explian the "power Draw" it states: "To calculate the power draw, the current must be multiplied with the battery voltage, as can be seen below it is about 1.2 volt under load and the light uses two batteries, the power is then (voltage*current): 1.2*2*1.6 -> 3.8 watt. Most of this power goes into the led where about 20% is converted to light, all the remaining power is converted to heat."
> but the photo below is of the tailcap measurements. I didnt get the reference to the "1.2v under load"... Are you saying to measure the battery " while in use" ?? and where did you get the "1.6" in the problem? was it, one battery measured 1.2v and the other measured 1.6v?
> Thank you!!



The 1.6 was the current draw, the battery is down to 1.2 volt when loaded.
Both alkaline and NiMH drops to around 1.2 volt while having a high load (i.e. 1+ amp) (This number is not an exact value, just a rule of thumb).

Tailcap measurements are (at best) a rough guide, but as long as you understand that, they are useful as a guideline to the current draw.


----------



## richardcpf

Can you point a good sub $100 multimeter? I want the fluke buy it is too expensive

I have 2 cheap $30 multimeter and both get different readings. The differences are huge, ranges 0.07v and 0.4A.


:thumbsdow


----------



## HKJ

richardcpf said:


> Can you point a good sub $100 multimeter? I want the fluke buy it is too expensive
> 
> I have 2 cheap $30 multimeter and both get different readings. The differences are huge, ranges 0.07v and 0.4A.



I can not point you to a specific meter, but there exist hundred of different meters in that price range, many (if not all) of them good for hobby use.

Some thing I would look for:


CAT III/CAT IV rating, this means the meter is safety rated for professional use.
Accuracy specification are more than just x%+y digits, there must also be specified some frequencies (for AC ranges) and some temperature limits. I.e.: "50 V range: 0.3%+25 at 45 to 65 Hz within 18 to 28 degrees" is a much more reliable specification than "AC: 0.3%+25"
The meter warns when the battery is low.
The 10A/20A range has a fuse.
The meter has a max reading of at least 3999, not only 1999. For measuring LiIon batteries an even higher value is better.
I also like that the meter has "True RMS", but it is not required for hobby meter.

I do not know if you can get all of the above below $100.


----------



## HKJ

I have added a chapter on low ohmic measurement.


----------



## Bullzeyebill

Interesting the differences in mOhm measurements of tailcap using the DMM only, and the DMM, resistor, and power supply. Fluke alone read 20mOhm resistance, and DMM, resistor, and power supply setup ended up showing 34mOhm resistance.

Bill


----------



## HKJ

Bullzeyebill said:


> Interesting the differences in mOhm measurements of tailcap using the DMM only, and the DMM, resistor, and power supply. Fluke alone read 20mOhm resistance, and DMM, resistor, and power supply setup ended up showing 34mOhm resistance.



No, my direct measurement did show 0.2 ohm, that is 200 mOhm and 0.13 ohm (130 mOhm) with shorted probes. This gives a result around 70 mOhm and includes connection resistance between probes and tailcap.


----------



## aingel2k1

Hi, Had a question about "light dimming" once in a while my light will "dim" after a few minutes, battery is not dead... will still have bout 3v sometimes even 3.5v, these are Recahrgeables... what would I need to check to see if theres a problem? could it be "bulb" requiring too much in the way of "amps", bad batteries, bad connection in light?? any comments are appreciated...
Thanks...


----------



## wquiles

HKJ - very nice guide :twothumbs


----------



## HKJ

aingel2k1 said:


> Hi, Had a question about "light dimming" once in a while my light will "dim" after a few minutes, battery is not dead... will still have bout 3v sometimes even 3.5v, these are Recahrgeables... what would I need to check to see if theres a problem? could it be "bulb" requiring too much in the way of "amps", bad batteries, bad connection in light?? any comments are appreciated...
> Thanks...



3 and 3.5 volt is empty for LiIon batteries at least with no load, maybe you battery is just about dead.
Try another battery and see if the problem goes away. It would also be a good idea to clean all connections.


----------



## HKJ

Added more measurements to the guide:

Current consumption, using resistor.
Power consumption.
Charge voltage: How to measure charge voltage in a charger.

And a table of contents.


----------



## rpaloalto

Thanks, I have been wondering about the output current on a few of my chargers. The tin foil and paper sandwich is a nice idea. Makes getting reading easy.


----------



## VidPro

HKJ said:


> Added more measurements to the guide:
> Current consumption, using resistor.
> Power consumption.
> Charge voltage: How to measure charge voltage in a charger.
> And a table of contents.



Gosh HKJ , could it get any better, i think you have outdone yourself :twothumbsexcellent work.


----------



## Jack Reacher

Cheers HKJ...

For another newbie like me, that's a great guide, particularly with the pics. Thank you for putting so much time and effort into producing it.

—Jack.


----------



## Nil Einne

Thanks for the great guide. I wasn't aware the meter turning off would cause no problems to measuring current. Am I right that no power is consumed from the internal battery either when the meter is off even if still part of a circuit? 

Cheers


----------



## Mr Happy

Nil Einne said:


> Thanks for the great guide. I wasn't aware the meter turning off would cause no problems to measuring current. Am I right that no power is consumed from the internal battery either when the meter is off even if still part of a circuit?


The battery is used for two purposes in a DMM:


To run the internal electronics and LCD display;
To feed current through the circuit when measuring resistance.
In advanced meters it might have some other purposes such as signal injection, but in ordinary meters that is all the battery is used for. So if the meter is turned off the battery is not being consumed.


----------



## HKJ

Nil Einne said:


> Thanks for the great guide. I wasn't aware the meter turning off would cause no problems to measuring current. Am I right that no power is consumed from the internal battery either when the meter is off even if still part of a circuit?
> 
> Cheers



Turning the meter off might affect the current measurement, if the power is controlled with the range selector switch. But letting the meter turn itself off will usual not change range, because the range selector stays in the same position.

When the meter turns itself off, it will probably still use a small amount of power, this has nothing with being part of the circuit to do.


----------



## AFAustin

May a non-technical guy please pose a question? After many years of faithful service, my budget DMM is acting strangely. When I first turn it on, it measures a cell's voltage too low, and then gradually measures it more accurately as a few minutes go by. 

I changed the battery, but that hasn't solved the problem. Just now, it seemed worse---it won't show a fully charged AAA NiMH cell at more than ~1.23v, when I know it should be closer to 1.35v.

Any advice would be appreciated. Thanks.

Andrew


----------



## Mr Happy

I have inexpensive meters that sometimes behave a bit like that after a period of non-use. In my case I put it down to oxidation on the contacts of the rotary switch leading to poor contact. Sometimes I can fix it a bit by rotating the switch vigorously between settings a few times before using the meter. I don't know if there is a really good cure -- you tend to get what you pay for, and such things may be more likely with budget meters.


----------



## HKJ

AFAustin said:


> May a non-technical guy please pose a question? After many years of faithful service, my budget DMM is acting strangely. When I first turn it on, it measures a cell's voltage too low, and then gradually measures it more accurately as a few minutes go by.
> 
> I changed the battery, but that hasn't solved the problem. Just now, it seemed worse---it won't show a fully charged AAA NiMH cell at more than ~1.23v, when I know it should be closer to 1.35v.
> 
> Any advice would be appreciated. Thanks.
> 
> Andrew



My first thought was flat battery, but you sort of spoiled that (Are you sure the new battery is working).

Next point is oxidation on the rotary switch, if you can, try opening the meter and clean the switch, maybe use some deoxit.

The best solution is to buy a good meter (My preference is Fluke), but that is a bit expensive.

The next best solution is to use a few $ on a new meter and maybe a cheap calibration unit/voltage reference (The best/cheapest way to verify that a meter works).


----------



## AFAustin

Thanks, Mr Happy and HKJ.

I will follow your suggestions and report back.

Andrew


----------



## AFAustin

Oxidation on the contacts of the rotary switch must be it---I vigorously rotated the switch a number of times, and voila'---working like a champ again. :thumbsup:

I removed the cover, thinking I'd try cleaning and applying DeOxit to the contacts, but the circuit board is a bit difficult to remove. For now, I will leave well enough alone.

Thanks again, gents, for your help. I really appreciate it.

Andrew


----------



## kosPap

hmm if there is stoll room for DMM trouble shooting what is the reason for one not zeroing....at times it reads (standalone)0.11V or more..some things happens with A measurements.....

it is not a batetry thing not a calibrating issue (have accessed the rotary dial (a resitor) taht zeros the readings....

toasted maybe?


----------



## Mr Happy

kosPap said:


> hmm if there is stoll room for DMM trouble shooting what is the reason for one not zeroing....at times it reads (standalone)0.11V or more..some things happens with A measurements.....
> 
> it is not a batetry thing not a calibrating issue (have accessed the rotary dial (a resitor) taht zeros the readings....
> 
> toasted maybe?


What does it read on DC V if you short the probes together?


----------



## kosPap

still the same number


----------



## uk_caver

I had something like that happen after blowing a fuse, but then (fairly obviously) all the functions that ran through that fuse stopped working.


----------



## Mr Happy

Most DMMs give non-zero indications on the volts ranges while the probes are unconnected due to static charges on the inputs. They will only read zero if you short the probes together. I have never owned a meter that didn't read zero when I shorted the probes.

It's probably a bad idea to adjust any of the internal calibration pots unless you have suitable calibration references to use and you know exactly what you are doing. 

If you have turned any of those potentiometers since the meter was originally calibrated you might have thrown the readings off.


----------



## wquiles

Mr Happy said:


> It's probably a bad idea to adjust any of the internal calibration pots unless you have suitable calibration references to use and you know exactly what you are doing.



+1

I got me one of these 1-2 years ago. It is awesome to routinely check my Fluke DMM's:
highly stable 5Volt reference

And my Flukes are still very accurate:






















and the same guy now sells another one that also offers current and resistance checks (probably a better buy price-wise):
DMM DVM Tester Checker Calibrator Voltage Reference

I have no affiliation with the seller - I am just a happy customer.


----------



## Bullzeyebill

Will, will that checker for current, if the DMM calibrates to that 1.000A accuracy, hold up when measuring, say, 5A's? So, 5A's exactly?

Bill


----------



## wquiles

Bullzeyebill said:


> Will, will that checker for current, if the DMM calibrates to that 1.000A accuracy, hold up when measuring, say, 5A's? So, 5A's exactly?
> 
> Bill



Bill,

I don't have the current checker, only the voltage checker, but basically yes. Once you "correct" the calibration factor, which causes the true value to deviate as components age, drift, etc., the meter should then be again accurate to within what is designed to do. These are for example the specs on my Fluke 289:
http://us.fluke.com/fluke/usen/digital-multimeters/fluke-289.htm?PID=56061&trck=289specifications

Corporations/ labs/engineering groups routinely send out their measuring equipment to be calibrated (sometimes yearly) to ensure that their results are meaningful. It is no good to have great resolution if the result lacks accuracy.


----------



## Meterman

Bullzeyebill said:


> Will, will that checker for current, if the DMM calibrates to that 1.000A accuracy, hold up when measuring, say, 5A's? So, 5A's exactly?
> 
> Bill




The "DMM DVM Tester Checker Calibrator Voltage Reference" delivers 1.000*m*A, so you only test the range 1mA. A good closeness _there_ does _not necessarily_ imply precision in the 5A range.  

When an instrument is to be calibrated, _every_ range is examined and adjusted individually.

Wulf


----------



## Bullzeyebill

Meterman said:


> The "DMM DVM Tester Checker Calibrator Voltage Reference" delivers 1.000*m*A, so you only test the range 1mA. A good closeness _there_ does _not necessarily_ imply precision in the 5A range.
> 
> When an instrument is to be calibrated, _every_ range is examined and adjusted individually.
> 
> Wulf



Thanks for correction. Yes, I did read the spec wrong.

Bill


----------



## wquiles

Bullzeyebill said:


> Thanks for correction. Yes, I did read the spec wrong.
> 
> Bill



Same here. Sorry about that :green:


----------



## Bullzeyebill

Going back to DC current measurements what would be an ideal resistor for measuring 3-8A's?

Bill


----------



## HKJ

Bullzeyebill said:


> Going back to DC current measurements what would be an ideal resistor for measuring 3-8A's?
> 
> Bill



That depends on what you are going to measure, i.e. how big voltage drop you can accept.
If it is a direct drive led from a single LiIon, without any series resistor, you need a very low voltage drop. A 0.01 ohm resistor would work, but you need to be very careful with the connection from the resistor to the flashlight and battery, they could add considerable resistance to the connection.
If you are working with 2xLiIon and a buck driver, you do not need to worry as much about voltage drop and a 0.1 ohm resistor (0.8 volt drop at 8 amp) would do fine.


----------



## njet212

HKJ said:


> It sound like you are measuring volts at the battery, not at the light. The meter and wires can easily drop a few tenths of volts.









I did things just like on your picture. I'm bit confused, if i'm doing thing just like your pic, I'm I measuring volt battery or current draw? :thinking:


----------



## HKJ

njet212 said:


> I did things just like on your picture. I'm bit confused, if i'm doing thing just like your pic, I'm I measuring volt battery or current draw? :thinking:



That way you measure the current draw *only*, but not at a specific voltage. The voltage you measure before or after, on the battery, is without load and will be considerable higher than when you measured the current draw (especially when we are talking about the Preon ReVo at high).

When doing this kind of current measurement it is best to use a fresh (or freshly charged) battery and then only specify battery type, not voltage.


----------



## njet212

Thanks for the answer HKJ, appreciate that!


----------



## fisk-king

Great work & thread:thumbsup:


----------



## njet212

HKJ, last time was asking about how do you measure standby current on a flashlight and you did answer it already. But today i tried to look at it again but i realized your post was missing. 

Would you mind to explain it again ? the flashlight i'm going to measure is New Jetbeam RRT-0 Infinite Variable Brightness version. I was wondering how much is the standby current because it's suck all the juice on my AW RCR123 just only in a week !!


Thanks


----------



## HKJ

njet212 said:


> HKJ, last time was asking about how do you measure standby current on a flashlight and you did answer it already. But today i tried to look at it again but i realized your post was missing.
> 
> Would you mind to explain it again ? the flashlight i'm going to measure is New Jetbeam RRT-0 Infinite Variable Brightness version. I was wondering how much is the standby current because it's suck all the juice on my AW RCR123 just only in a week !!



That light is supposed to have a real on/off switch, i.e. no current draw when switched off on the tail switch. If you want to measure the current draw with the ring in off position, you can just use the "Current consumption" chapter, but you will need to use the "mA" socket, not the "A" socket.


----------



## njet212

Thanks for your answer HKJ :thumbsup:


----------



## brightnorm

HKJ,

Many thanks for posting this. It is extremely helpul and beautifully illustrated and explained. 

Brightnorm


----------



## HKJ

Added a "High current measurement" showing how to use a clamp meter.


----------



## Walterk

Very nice ! And clearly illustrated, thx for this thread.


----------



## Viking

I have a cheap Velleman DVM92 multimeter.


Specs are:


3 ½ digit ( maximum display 1999 )
Accuracy DC voltage +/- 0,5% of rgd +/- 1 digit
Accuracy DC current 20mA +/- 0,8% of rgd +/- 1 digit
Accuracy DC current 200mA +/- 1,2% of rgd +/- 1 digit
Accuracy DC current 20A +/- 2% of rgd +/- 5 digits


Is the DMM accurate enough for measuring flashlight batteries , or will you recomend me buying a better one.


----------



## HKJ

Viking said:


> 3 ½ digit ( maximum display 1999 )
> Accuracy DC voltage +/- 0,5% of rgd +/- 1 digit
> 
> Is the DMM accurate enough for measuring flashlight batteries , or will you recomend me buying a better one.



For LiIon batteries the charge voltage is usual 4.2 volt +/- 0.05 volt, as long as you batteries does not read above 4.2 volt on you DMM they are below 4.25 volt (According to the DMM specification below 4.23 volt).
Most chargers will be more than good enough and you do not need to check the batteries each time you take them off the charger.
Where it is important to check batteries is when you run them down, many LiIon batteries can get dangerous if you discharge them to low, to check this does not require much precision from the meter. If the battery measures below 2.5 to 3 volt (After they have rested some time), there is a risk they may explode when charged. This is a cumulative effect, each time they get discharged to much the risk for explosion during any subsequent charge will increase slightly.

Batteries that show 0 volt on the meter might not be discharged to much, it is probably the protection that is tripped. If you charger can reset a protection (See my charger reviews), give the cell a second in the charger, then take it out and check the voltage again. If the charger cannot reset protection you need to wire it parallel with another LiIon cell for a second.

And if you DMM's reading suddenly are a bit beside the expected values, you probably need to replace the battery in the meter.


----------



## Viking

Thanks for the answer


----------



## Tohuwabohu

HKJ said:


> The tailcap is removed from the flashlight and the meter is substituted for that connection, i.e. one probe pin is placed on the battery and the other probe pin is placed on the battery tube, where there is some bare metal. Placing the probe pin on anodized metal will not work.
> As can be seen, the two meters do not agree on the value. That is because the current draw is not really DC, but drawn in very fast pulses, the meters does not sum this the same way. This is only a problem on some flashlights.


Hello HKJ,
have you ever tested the resistance of the probe leads of the cheap DMM?
I got a Best DT9205A today to compare it too a good multimeter. The DT9205A is not very accurate but usable but the probe leads are crap, their resistance is far too high. I measured 0.46 ohms - ten times the value of some probe leads from another meter and more than 50 times the value of a pair of short leads with banana plugs on both ends.
I don't think that fast pulses cause the wrong reading but the voltage drop across the probe leads makes the regulated light draw a higher current.
Of course the effect of the high probe lead resistance gets worse with pulsed currents.


----------



## HKJ

Tohuwabohu said:


> Hello HKJ,
> have you ever tested the resistance of the probe leads of the cheap DMM?
> I got a Best DT9205A today to compare it too a good multimeter. The DT9205A is not very accurate but usable but the probe leads are crap, their resistance is far too high. I measured 0.46 ohms - ten times the value of some probe leads from another meter and more than 50 times the value of a pair of short leads with banana plugs on both ends.
> I don't think that fast pulses cause the wrong reading but the voltage drop across the probe leads makes the regulated light draw a higher current.
> Of course the effect of the high probe lead resistance gets worse with pulsed currents.



The test leads is probable part of the reason.

I have been testing some leads, switches and dmm's:

JetBeam M2S Tailcap
70 mohmThruNite TN11 Tailcap85 mohm4Sevens Quark X AA2 Tailcap82 mohmFluke 289 10A range33 mohmFluke 189 10A range55 mohmFluke 179 10A range35 mohmVichy VC99 20A range48 mohmBest DT9205A 20A range18 mohmFluke test lead (x1)38 mohmFluke test lead (x1)51 mohmNo name test lead (x1)
257 mohmNo name 10A test lead (x1)
22 mohm


Doing a test with 10A current and measuring the voltage from test probe tip to test probe tip:


 10ATot. ResFluke 289 + Fluke test lead1.02 volt102 mohmFluke 189 + Fluke test lead1.16 volt116 mohmFluke 179 + Fluke test lead0.97 volt97 mohmBest DT9205A + No name 10A test lead
0.59 volt59 mohm
The connection resistance from test probe tip to current source is not included.


----------



## tobrien

so the ZTS battery tester (the one that supports 3.7V li-ions) _*can*_ do protected cells fine?


----------



## HKJ

tobrien said:


> so the ZTS battery tester (the one that supports 3.7V li-ions) _*can*_ do protected cells fine?



Yes, there is no difference between a protected and unprotected cell in this regards.


----------



## tobrien

HKJ said:


> Yes, there is no difference between a protected and unprotected cell in this regards.


oh okay, thank you! I had been misinformed in the past that the protection circuits kept those cells from being accurately tested by the pulse load.


----------



## dragosios

I see that many of you ask why some multimeters do not display zero.
For TrueRMS meters this is normal. They will not display zero, it's about how the processor makes the measurement.
On Flukes seen here: 87, 179, 189, etc, calibration manual tells you which value is the calibration check on each scale. Eg: a Fluke 189 that has 5.0000 on it's input and reads between 4.9997 and 5.0023 then it's in spec. Next value is ten times the first one, in this case 50V and 500V DC.
Good probes are below 0.1ohms each. Cheap chinese one are higher than that.
Measurement of very low resistance can be done conveniently with an AC ohmmeter, or ESR meter.


----------



## loquutis79

I want to check the open voltage of my battery charger, and I think this is what you call it when its plugged in and no battery installed. [Sorry, not much electrical knowledge]
My charger is labled at 4.2V output. Do I simply plug it in and attach each DMM probe [auto range set to AC V?] to the pos. and neg. sides of one channel?
When I did the above I get a reading of .027V?? on the auto range setting. 

Does this make sence?


----------



## flashlight chronic

My DMM set on DC reads 4.87v off my WF-139 charger.


----------



## HKJ

loquutis79 said:


> I want to check the open voltage of my battery charger, and I think this is what you call it when its plugged in and no battery installed. [Sorry, not much electrical knowledge]
> My charger is labled at 4.2V output. Do I simply plug it in and attach each DMM probe [auto range set to AC V?] to the pos. and neg. sides of one channel?
> When I did the above I get a reading of .027V?? on the auto range setting.
> 
> Does this make sence?



Evert thing except the AC V part makes sense, try using DC V.

But the open voltage does not say much about anything, the charger is electronically controlled and the open voltage might be above or below 4.2 volt, depending on how the electronic does the controlling.


----------



## loquutis79

That makes more sence now. Told you I know little about electrical stuff :], but willing to learn.

OK, now I get 4.2 from both channels.

Just trying to learn as much as I can, and like to re produce some of the tests I see here on the site. While waiting for a Pila charger for my 18650's I am using an Ultrafire WF139 [don't throw anything at me!], and as there are so many negitive posts I want to check things out where I can.


Thanks for the supper fast replies from you both. Now I can tell the wife that its not just me who spends weekend mornings reading about flashlight stuff.


----------



## loquutis79

So what I did next was to check voltage during testing. I did the tin foil at both ends of the 18650 while in the charger and attached the DMM leads to each side.
As I knew the batteries were fully charged just last night, minus a bit of playing on turbo after that, I knew that it should not take long to light up the green lights on the WF139. 
So I watched for the few minutes until the light changed and what I saw was the following:
1st -red light = charging. 4.21V-4.24V during this stage.
2nd-green light = full charge. DMM jumped right to 4.59V
I left it on only for a couple of minutes and then pulled the plug.
Results = hurry up with the Pila charger order??
Or did I miss something here also. It that an viable test?


----------



## HKJ

loquutis79 said:


> 2nd-green light = full charge. DMM jumped right to 4.59V
> I left it on only for a couple of minutes and then pulled the plug.
> Results = hurry up with the Pila charger order??
> Or did I miss something here also. It that an viable test?



Do not worry to much about the voltage, that was because the over charge protection in the battery tripped. The charger would have stopped soon enough if it had not tripped. The "problem" with the WF-139 is that it measures the voltage with the current turned off and that means it goes above 4.2 volt with the current on (The current on/off is to fast to reliable measure with a DMM).

I had the same happen when I tested the WF-139.


----------



## rjking

Hi HKJ, can you recommend a Fluke DMM mainly to test and check batterries voltages and Mah?


----------



## uk_caver

A DMM isn't any use for measuring mAh (battery capacity), unless you use it to make repeated measurements of cell voltage as a cell or battery is discharged at a known current.


----------



## HKJ

rjking said:


> Hi HKJ, can you recommend a Fluke DMM mainly to test and check batterries voltages and Mah?



Measuring mAh is not something you can just do with a DMM, a hobby charger is much better for it.

I often use a Fluke 179 DMM for various tasks, but for just checking batteries it is way to expensive, a Fluke 115 would do for that. 
The 115 has a 6000 scale, i.e. you will get battery voltage with 3 decimal digits, but the DMM is missing the low current ranges and cannot be used to measure low modes current draw and standby current with.


----------



## rjking

uk_caver said:


> A DMM isn't any use for measuring mAh (battery capacity), unless you use it to make repeated measurements of cell voltage as a cell or battery is discharged at a known current.





HKJ said:


> Measuring mAh is not something you can just do with a DMM, a hobby charger is much better for it.
> 
> I often use a Fluke 179 DMM for various tasks, but for just checking batteries it is way to expensive, a Fluke 115 would do for that.
> The 115 has a 6000 scale, i.e. you will get battery voltage with 3 decimal digits, but the DMM is missing the low current ranges and cannot be used to measure low modes current draw and standby current with.



Oh okay. So the only way I can make sure that i'm putting 2 x CR 123 or 2 x 18650 with similar capacity level is by checking on their voltage then, is that correct? Man, that Fluke 115 is way too expensive. Thought, there's something half the cost.


----------



## HKJ

rjking said:


> Oh okay. So the only way I can make sure that i'm putting 2 x CR 123 or 2 x 18650 with similar capacity level is by checking on their voltage then, is that correct?



Yes.



rjking said:


> Man, that Fluke 115 is way too expensive. Thought, there's something half the cost.



Fluke is rather expensive.
For checking batteries just about any cheap DMM can be used, but many cheap DMM's shows a wrong value when the batteries are running low.
If you want something more than a cheap DMM, then a good DMM for the price is UNI-T UT61E.

You can also get a "cheap" Fluke (17B), but it is only sold in China (You can find it on Ebay). It looks like a decent DMM.


----------



## staffyman

So, I've read your guide, but I'm none the wiser.:duh2:

Nothing at all to do with the guide, it's me - I need to read things over and over again before it sinks in.

I'm not very savvy with electronics either but if I read it a few times and keep referring back to it when needed then I'm sure I'll be ok.

My multimeter came with a little booklet but only gives specs and isn't a guide to how to use it.

I've only ever used it to measure that voltage is present but now I can refer to your guide, I'll be able to use it correctly.

Many thanks.:thumbsup:


----------



## Planz

"To get a better idea about how it will work in a flashlight, I need a load on the battery, here I am using a 1ohm resistor. The battery still maintains voltage enough to drive a flashlight. The resistor must be at least 3 watt, but a resistor rated for a higher wattage (i.e. 10 watt) is much better, because it will stay cool.





 





Next battery is a LiIon 18650 battery, this requires the 20V range, the battery has 4.17 volt. For a LiIon this means that it just about fully charged. The voltages for a _LiIon must be measured without load_ and are: Fully charged 4.2V, empty 3.6V
When getting a new LiIon charger it can be a good idea to check the voltage, on the cells, when they are removed from the charger, they must not be above 4.3V, it is much better if they are at 4.2V."

Hi HKJ,
Could I ask why a LiIon must be measured without load whereas an Alkaline or NiMH needs to be measured with load in order to gauge the energy level of the battery? What happens if you measure a LiIon with load?
Thanks.


----------



## HKJ

Planz said:


> Hi HKJ,
> Could I ask why a LiIon must be measured without load whereas an Alkaline or NiMH needs to be measured with load in order to gauge the energy level of the battery? What happens if you measure a LiIon with load?



You can measure LiIon with load, but the tables listing how much energy is remaining will not be correct.
Measuring Alkaline or NiMH without load will show them as nearly full, even if they are close to empty.


----------



## Planz

Got it. Thanks!


----------



## OneBigDay

Wanted to say *thanks* for this guide and let HKJ know some of us are using it.

A few years ago this was the first guide I saw to show me how to check voltage on my cells. Little did I know how frequently I would be doing this the more I got into things. I have also diagnosed two bad McClicky switches with the tailcap part of the guide; one of them just today. Good stuff.


----------



## RI Chevy

I agree wholeheartedly! It is a great resource, and Henrik is a great member! Thank you. :thumbsup:


----------



## kosPap

OneBigDay said:


> A few years ago this was the first guide I saw to show me how to check voltage on my cells. Little did I know how frequently I would be doing this the more I got into things. I have also diagnosed two bad McClicky switches with the tailcap part of the guide; one of them just today. Good stuff.



I am in the process of monitoring battery aging by measuring their Internal Resistance.
Another thumb up for HKJ


----------



## HKJ

kosPap said:


> I am in the process of monitoring battery aging by measuring their Internal Resistance.



Did you see my writing about that: http://lygte-info.dk/info/Internal impedance UK.html


----------



## kosPap

Yes i did...And if i hadn't , i would never sit down and do it.....
It has opened my eyes on how my 18650s age and helped me avoid a 4x battery combiantion that one 18650 had increased resistance (some batteries, rarely used, but with 1 year difference in production lot)

BTW I am using the "first" method, with a resistor that matches real life current draw at max output


----------



## applevalleyjoe

Just the info that I was looking for...thanks a lot.


----------



## IonicBond

HKJ said:


> I often use a Fluke 179 DMM for various tasks, but for just checking batteries it is way to expensive, a Fluke 115 would do for that. The 115 has a 6000 scale, i.e. you will get battery voltage with 3 decimal digits, but the DMM is missing the low current ranges and cannot be used to measure low modes current draw and standby current with.



I'll vouch for the Fluke 115 as being the least expensive multimeter you can trust out of the box. Or perhaps the 114 if you don't do any sort of current measuring with it. While the 115 doesn't have a milliamp range, it will measure below 1A, but the cutoff seems to be about 100ma. So it is not ideal for testing very low currents like you mentioned, and if you test led's, may not have enough voltage to light them brightly. It is after all an an electrician's meter, not an electronics oriented one. For that kind of use my 87V is brought out.

Most importantly, the min-max function, which also beeps audibly at changes of 1mv, has a very important function when working with li-ion. When a cell that is under discharge or charge, when you hit the steep charge/discharge knees, the meter starts to beep very fast - important for safety in case something goes wrong. You can also use it to know if you have suddenly dropped a cell, or if a cell that seems normal just goes berserk. With the audible beeps, you can catch this activity before it goes to the extremes. The beeps on the 11x series are a bit lower than say an 87V, as the piezo beeper is much smaller.

Also not mentioned about using cheap meters is their measuring speed, and some tendency for over and undershoot. The Flukes are plenty fast and are bang-on without nary an under or overshoot.

For me, working on li-ion without a quality meter is just asking for trouble. I also vote for HKJ's wonderful work to be a sticky!


----------



## 5S8Zh5

mbiraman said:


> Great job HKJ. I was wondering . On the ZTS battery tester under 3.6v you see listed a number of batteries but not 14500. My aw 14500's are 3.7. Does it matter ?? . Can the 14500's be tested in the 3.6 spot??





HKJ said:


> Yes, it can, it is about the same as RCR123A/16340.



I was reading the LiIon Battery tester section, and saw that you were using the ZTS MBT-1. I have the ZTS MINI-MBT, and it has the same 3.6V Lithium-Ion RCR123A, 18500, 17650 terminal for 14500 batteries. I was reading BU-409: Charging Lithium-ion - Over-discharging Lithium-ion: "Li-ion should never be discharged too low..."

Which percentage on the ZTS should be used for when it's time to charge a 14500 LiIon?


----------



## HKJ

5S8Zh5 said:


> I was reading the LiIon Battery tester section, and saw that you were using the ZTS MBT-1. I have the ZTS MINI-MBT, and it has the same 3.6V Lithium-Ion RCR123A, 18500, 17650 terminal for 14500 batteries. I was reading BU-409: Charging Lithium-ion - Over-discharging Lithium-ion: "Li-ion should never be discharged too low..."
> 
> Which percentage on the ZTS should be used for when it's time to charge a 14500 LiIon?



I have not checked it but 0% or 20%. I will expect 0% to signal empty, but not necessary over discharged.


----------



## 5S8Zh5

HKJ said:


> I have not checked it but 0% or 20%. I will expect 0% to signal empty, but not necessary over discharged.


Thanks. ...


----------



## Crazyeddiethefirst

Hi CPF & HKJ,
I have been using a DMM for years, thanks to learning of the importance of matching in multi-cell lights from CPF. I recently added a ZTS to measure load. Because I have an extensive collection of lights and rotate their use, I have a maintenance schedule for all lights to have threads & O rings lubed, a quick polish with a protectant and I check the cells. I have over 20 Surefire multicell lights and when testing I was shocked to find Surefire CR123A cells that measured 3.16 V on both cells but under load testing with the ZTS they only showed 20% capacity. This occurred on 3 different lights. A fourth light measured 3.12v on both cells but under load 1 cell was 20% and the other 60%. The remaining lights were all above 3.0v with 100% on load testing. I repeated all tests multiple times to rule out poor contact. None of the batteries are more than 3 years old. Any idea why the voltage would be good but under load fail? Am I correct in assuming these batteries should be moved to my Surefire Hurricane lamp or Joule thief since their runtime could leave me stranded? Thanks for any information you can provide.


----------



## SilverFox

Hello Crazyeddiethefirst,

If you are up for an experiment...

Test your low cells and note the ZTS value associated with each cell that is in question.

Take a cell that showed low capacity on the ZTS and put it into a single cell light that draws reasonable current. If you don't have any, pick two of the cells that showed low capacity and put them into a multi cell light.

Next turn the light on for 15 - 30 seconds, then shut it off.

Take the cells out and let them rest for 30 minutes, then test them again with the ZTS tester.

If the value from the ZTS increases, there is a good chance the cells have developed a pacification layer inside. Once you burn this layer off the cells may perform as normal, at least in the short term.

Tom


----------



## Crazyeddiethefirst

Tom,
Thank you for the guidance! I have plenty of one cell lights, I will get testing asap. What causes a pacification layer, and is there a cause that is avoidable? Thanks again, I really appreciate it!


----------



## m4a1usr

There is some pretty good reading material (as well as calculators) on Passivation and Depassivation on the Spectrum Batteries web site. Well worth a stroll down information lane.


----------



## SilverFox

Hello Crazyeddiethefirst,

I guess I should learn how to spell...

The information provided by M4a1usr seems to explain what is going on.

The topic of passivation came up a few years back when BatteryStation was having some issues with their CR123 cells. They were manufactured in China and while they performed well they did not store well. This prompted Kevin to change manufacturers to Panasonic and the issue went away, for the most part.

At that time I ran across a white paper by Energizer stating about the same thing as is listed in the Electrochem article. In part that was that applying a load to the cell can burn off the passivation layer and restore the cell to like new condition, minus a small amount of capacity.

Digging deeper it seems that additives can be added to the electrolyte to retard this layer from forming and cheaper manufacturing processes may reduce costs by eliminating those additives. Also, impurities in the electrolyte chemicals can contribute to this problem.

The ZTS tester applies a load to the cell. Sometimes all it takes is 5 - 8 repeats of the test to burn off the passivation. Other times it takes a decent load. And still other times nothing helps. I just checked some BatteryStation mismatched cells from 2006. The started out at 80% on the ZTS in 2006 and I have been storing them to see what happens. When I tested I got 0% from these cells. After running them in a single cell incandescent light for a short time, they rebounded to 10%. There are a lot of variables involved and that makes it difficult to come up with a set way to try to recover the cells. I just end up using them in single cell lights.

After a number of tests and extensive evaluation I have decided that the ZTS gives me a heads up that something is going on. From there I usually subject those cells to a brief load and then rotate them to be used immediately. There are far fewer problems with quality cells, but sometimes they crop up.

Tom


----------



## CoherentRays

Wow, I only just discovered this thread because some kind soul resurrected it from obscurity in the past by necro posting to it. Like others, I add my thanks to HKJ and nominate it for a sticky. 

Ed


----------



## Bullzeyebill

It's now a sticky.

Bill


----------



## CoherentRays

Bullzeyebill said:


> It's now a sticky.
> 
> Bill


Thank you, sir. :twothumbs

It will be much easier to find now when I'm trying to remember one of those more complex (to my mind anyway) techniques. 

Ed


----------



## Crazyeddiethefirst

SilverFox said:


> Hello Crazyeddiethefirst,
> 
> If you are up for an experiment...
> 
> Test your low cells and note the ZTS value associated with each cell that is in question.
> 
> Take a cell that showed low capacity on the ZTS and put it into a single cell light that draws reasonable current. If you don't have any, pick two of the cells that showed low capacity and put them into a multi cell light.
> 
> Next turn the light on for 15 - 30 seconds, then shut it off.
> 
> Take the cells out and let them rest for 30 minutes, then test them again with the ZTS tester.
> 
> If the value from the ZTS increases, there is a good chance the cells have developed a pacification layer inside. Once you burn this layer off the cells may perform as normal, at least in the short term.
> 
> Tom



Sorry for the delay, a few medical issues have kept me tied up. Well, I tried the testing as suggested, but no change if indeed it was caused by passivation. I tried using both LED & incandescent, in case the load was of consequence-no change.(there was no increase or decrease after application of load and recovery period). Any other ideas? Thanks!


----------



## SilverFox

Hello Crazyeddiethefirst,

Well...

Perhaps it is time to just move on.

Tom


----------



## Crazyeddiethefirst

I came to the same conclusion with one caveat-I am going to give Surefire a call and have a chat with them....thanks for your input!


----------



## maniac78

Very good guide! Could you someone explain how to measure the charging rate from a charger with the DMM ? It will be very helpful. Thanks


----------



## CivilGear

Wow great guide! Thanks for sharing!


----------



## jackolantern

Learned much from this thread! I read section on measuring power in flashlight. I don't have two meters and wonder what is method of measuring that with resistor. I did use resistor method to calculate current draw. Thanks for any reply.


----------



## HKJ

jackolantern said:


> Learned much from this thread! I read section on measuring power in flashlight. I don't have two meters and wonder what is method of measuring that with resistor. I did use resistor method to calculate current draw. Thanks for any reply.



You simply replace the ammeter with a resistor (0.1ohm or less) and the move the voltmeter between the flashlight voltage and the voltage across the resistor.
I have started a new series of articles about multimeters, this series is more general (i.e. not flashlight specific), until now I have published two articles (thermocouplers & current measurement) and more is planned.


----------



## MAD777

HKJ said:


> ...
> I have started a new series of articles about multimeters, this series is more general (i.e. not flashlight specific), until now I have published two articles (thermocouplers & current measurement) and more is planned.



Thank you HKJ for your valuable contributions to this community!


----------



## jackolantern

Much thanks HKJ. You're extensive contributions here and on your website is invaluable. Will definitely look for your writings regarding meters.


----------



## rickypanecatyl

Just read this 10 years after you wrote it - thanks for the write up! It was extremely helpful and obviously has a lot of work put into it! Rick


----------



## HKJ

rickypanecatyl said:


> Just read this 10 years after you wrote it - thanks for the write up! It was extremely helpful and obviously has a lot of work put into it! Rick



Lately I have been writing a lot more about multimeters:
Multimeter and component testing
Multimeter probes
Multimeter and voltage measurements
Multimeter and pulsed DC current (PWM)
Tolerance specifications for multimeters
Clamp meters magnetization, demagnetization and offset
Multimeters and current measurements
Multimeters and thermocouples

Multimeter design
Multimeter protection and safety

And also been reviewing some:
Multimeter selection table


----------



## MAD777

This is fantastic HKJ! Thank you!


----------



## Schermann

Measuring >10 Amps without blowing up your DMM...
...by making up a $2 shunt!

How to test high DC amperage (500+) using a DMM by making a Shunt that measures Amps as millivolts on a DMM, brilliant video explains all!




Setup from video:






Measuring locations on cable shunt:





Verification with amp clamp:





- - - - - - -

My Fluke 88v uses this simple shunt (no clamp needed) with ease to measure 600+ amps 'as millivolt' readings on my car alternator and no blown fuses...


----------

