# How do you use a multimeter??



## JimmerG (Dec 5, 2008)

Can someone help out here - I've just bought the multimeter shown below.. a Skytronic 600.005 - and I cannot get a proper battery reading out of it...

It's got a couple of battery testing clicks on the dial one for 1.5V (40mA) and 9V (24mA) If I link up a protected 18650 to the 9V setting, I get a reading of 10.4..

Can anyone explain to me exactly how to test an 18650 with a multimeter?


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## bguy (Dec 5, 2008)

Those battery testing settings are for regular 1.5V and 9V batteries, not lithium. For testing 18650s, just put it on DC voltage. On that meter you have to select the 20V range. The icon for DC is a line with dots under it.

Bradley


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## JimmerG (Dec 5, 2008)

Of course - it all makes sense... I'll give it a go.


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## JimmerG (Dec 5, 2008)

I've discovered where I went wrong - have the positive wire in the amps socket and not the volts socket - idiot.

So now I'm up and running with this multimeter - its as if a blindfold has been removed, finally I can see what's going on inside the cells.

It seems to measure 18650 fine - mine are coming off the charger at 4.18. It also seems to measure 1.2v Nimh cells fine aswell. 

I found this very usefull table in another CPF post for 18650 cells..

4.2 volts 100%
4.1 about 90%
4.0 about 80%
3.9 about 60%
3.8 about 40%
3.7 about 20%
3.6 empty for practical purposes
<3.5 = over-discharged

Does anyone know is there's an AA 1.2 Nimh version?


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## SilverFox (Dec 5, 2008)

Hello Jimmer,

There isn't a similar table for NiMh...

The voltage with this chemistry remains flatter making it difficult to interpret. For example a cell that is completely discharged will have an open circuit voltage of 1.2 volts or over. The best way to measure NiMh cells is to apply a load to them and measure the voltage under load. This also has difficulties, but gives a better indication of the state of charge of the cell.

Tom


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## 45/70 (Dec 5, 2008)

You can't really check the condition of a nickel based rechargeable battery by measuring open circuit voltage, however it is generally accepted that if you obtain a reading of 1.2 Volts or less, the cell is dead.

Dave


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## hopkins (Dec 5, 2008)

putting a load of a 10 ohm resistor (or in that range) on a Nimh cell
while measuring the voltage gives you a good idea of its 'state of charge'

approximatly ---- 1.37volts is full ----- 1.16volts is empty and time to recharge.





Sort of like your car gas tank -empty means you better get to a gas station before it is really empty., NimH empty means better recharge before the cell chemicals are damaged by over discharge and loses capacity and life (number of charge cycles)


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## SkipH (Dec 6, 2008)

How many watts does the 10 ohm resistor need to be so it won't go  while doing this test?



hopkins said:


> putting a load of a 10 ohm resistor (or in that range) on a Nimh cell
> while measuring the voltage gives you a good idea of its 'state of charge'
> 
> approximatly ---- 1.37volts is full ----- 1.16volts is empty and time to recharge.
> ...


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## VidPro (Dec 6, 2008)

SkipH said:


> How many watts does the 10 ohm resistor need to be so it won't go  while doing this test?


 
just get one of these
http://www.radioshack.com/product/index.jsp?productId=2062291
and you can do about anything without flames 

picture shows the 2W one, but the idea is the same.
if you get a nice fat 10W resister, you have the space, and you can toss it across about anything from a AA to a car battery without it charring up.
and then it wont CHANGE ever, because a carbon one overloaded will change resistance, which wont help keeping things contant for comparison.

also note that whenever the battery is connected TO it, it will be drawing off power from the battery (as if you didnt know)


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## SkipH (Dec 6, 2008)

Thanks for the info....I think I've got one like that somewhere....used it for loading up computer power supplies to get hard disks to come on...time for a trip to the junk box.



VidPro said:


> just get one of these
> http://www.radioshack.com/product/index.jsp?productId=2062291
> and you can do about anything without flames
> 
> ...


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## Mr Happy (Dec 6, 2008)

VidPro said:


> a car battery


Yeah, I'd be a bit careful there. At 12 V, the power in a 10 ohm resistor is going to be:

W = V²/R = 144/10 = 14.4 W

If you are holding onto that resistor with your bare hands at the time you are in danger of burning your fingers


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## labrat (Dec 7, 2008)

JimmerG said:


> I've discovered where I went wrong - have the positive wire in the amps socket and not the volts socket - idiot.
> 
> So now I'm up and running with this multimeter - its as if a blindfold has been removed, finally I can see what's going on inside the cells.
> 
> ...



You cannot trust these measurements for LiIon cells.
16350 or 18650 cells, I have had a couple of cells that read 4.20 Volts after charging, but the ZTS meter shows no charge, and trying to read any power output from them gives hardly 250 mA output just shorted through the meter!
They are gone! Empty.Ready for recycling.
Same goes for NiMh.
The above mentioned trick with a load resistor is better and more accurate, just don't hook up too long!


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## divine (Dec 7, 2008)

Let's see here. This is how you check the "open" voltage of the cell.

I drew a black line to show where you put the setting on the meter. The horizontal solid line next to the horizontal dotted line means DC, the 2 means you're setting your range to be 1-10 volts, com is your negative, and the V is your positive voltage.

Yes, I know this is a rough example! :laughing:


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## 45/70 (Dec 7, 2008)

divine said:


>





Generally, I find testing 3.7 Volt cells works better on the 20 Volt scale than the 2 Volt scale, when those are the choices.  Sorry divine, just couldn't resist! 

Dave


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## labrat (Dec 7, 2008)

45/70 said:


> You can't really check the condition of a nickel based rechargeable battery by measuring open circuit voltage, however it is generally accepted that if you obtain a reading of 1.2 Volts or less, the cell is dead.
> 
> Dave



NiMh cells have a nominal Voltage of 1.2 Volts.
To regard them as "dead" if you read an open voltage of 1.2 Volts, is not correct.


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## Illum (Dec 7, 2008)

if your buying a multimeter purely for measuring batteries, I would suggest buying one of these instead
http://www.lighthound.com/ZTS-MBT-1...-37-volt-rechargeable-batteries_p_6-2389.html

yes, its a tad expensive, but like its ZTS brothers uses a low curent load to test the capacity of cells rather than interpretation by voltage:twothumbs
I have the ZTS mini, this ones fully loaded with button cells AND lithium ions [note: although it only states RCR123A, 18500, 17650, 18650 on the cover al lithium-ions behave the same in terms of voltage, 4.2 = full, 3.7 = dead]


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## 45/70 (Dec 7, 2008)

labrat said:


> NiMh cells have a *nominal* Voltage of 1.2 Volts.
> To regard them as "dead" if you read an *open* voltage of 1.2 Volts, is not correct.


nominal=under load

Wattnot ...... eh, nevermind. 

Dave


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## divine (Dec 7, 2008)

45/70 said:


> Generally, I find testing 3.7 Volt cells works better on the 20 Volt scale than the 2 Volt scale, when those are the choices.  Sorry divine, just couldn't resist!
> 
> Dave


:laughing:


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## labrat (Dec 8, 2008)

45/70 said:


> nominal=under load
> 
> Wattnot ...... eh, nevermind.
> 
> Dave




http://en.wikipedia.org/wiki/Nickel-metal_hydride_battery


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## Mr Happy (Dec 8, 2008)

labrat said:


> NiMh cells have a nominal Voltage of 1.2 Volts.
> To regard them as "dead" if you read an open voltage of 1.2 Volts, is not correct.


No, it's true. If an NiMH cell reads 1.2 volts open circuit, it indicates that it is fully discharged. A fully charged cell should read 1.35 volts or more.

If an NiMH cell ever shows a resting voltage much lower than 1.2, it is a sign that it is either defective or damaged.


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## jzmtl (Dec 8, 2008)

labrat said:


> You cannot trust these measurements for LiIon cells.
> 16350 or 18650 cells, I have had a couple of cells that read 4.20 Volts after charging, but the ZTS meter shows no charge, and trying to read any power output from them gives hardly 250 mA output just shorted through the meter!
> They are gone! Empty.Ready for recycling.
> Same goes for NiMh.
> The above mentioned trick with a load resistor is better and more accurate, just don't hook up too long!



Well those numbers are assuming your cell isn't dead. Dead cells can charge up to normal resting voltage but will drop rapidly under load. If yours only give 250ma when shorted then they are, not the same thing here.


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## silverwarior (Dec 8, 2008)

Can't afford a ZTS at the moment  & using DMM to measure battery voltage is something new to me but there is one doubt. Why do we need to connect a 10 ohm resistor when measuring NiMH battery? Is it apply to NiMH battery only or all others rechargeable battery as well?

i've tried searching CPF for the answer but no luck. i came across one guide at other website & the fellow actually measuring NiMH battery voltage without any resistor. 

http://www.basicxandrobotics.com/tutorials/battery%20check/index.html

i am confused 

Hopefully a CPFer can clear my doubt. Thanks in advance!!

Silver


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## labrat (Dec 8, 2008)

As I have tried to tell earlier, a cell can still give a full reading of Voltage, even if the cell is dead or ruined/defective.
That manual is OK, you should be able to understand how to measure open Voltage on a cell, without any load.
But as said, that is not conclusive of the status of the cell!
Applying a load when doing a measurement of a cell, you make the cell work up, it has to deliver power as well, Amperes, when you do the measurement.
And a defective/dead cell will show because it cannot give out any power/Amperes.
And thus the Voltage too will be low, or nothing!
This applies for all cells, NiMh or LiIon, or any other chemistry.


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## silverwarior (Dec 8, 2008)

labrat said:


> As I have tried to tell earlier, a cell can still give a full reading of Voltage, even if the cell is dead or ruined/defective.
> That manual is OK, you should be able to understand how to measure open Voltage on a cell, without any load.
> But as said, that is not conclusive of the status of the cell!
> Applying a load when doing a measurement of a cell, you make the cell work up, it has to deliver power as well, Amperes, when you do the measurement.
> ...


 
Now i got it, Thanks for the explanation, Labrat!  

i recall reading somewhere that the lead must not connect to the battery for too long when taking measurement. Is it because it will drain the battery power or it will go  for Li-ion battery?


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## labrat (Dec 8, 2008)

The load will draw power, Amperes, and depending of the type of cell this can be quite a lot.
A good RCR123 LiIon cell can push out up to 18-19 Amperes!
An 18650 LiIon cell even more!
And this will make the load produce heat, as well as if you make the cell pump out too much, the cell can go  !!
So doing these measurements, drawing a lot of Amperes from the cell, you try to minimize the time the leads are connected/the load is applied.
Try to connect a second most, your DMM should be able to get a reading by that time.
If your DMM has a "Hold" function, use that and do the readout after you have disconnected the battery!
Any loss of charge is no problem, these are rechargeable cells we are talking about?!


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## silverwarior (Dec 9, 2008)

labrat said:


> The load will draw power, Amperes, and depending of the type of cell this can be quite a lot.
> A good RCR123 LiIon cell can push out up to 18-19 Amperes!
> An 18650 LiIon cell even more!
> And this will make the load produce heat, as well as if you make the cell pump out too much, the cell can go  !!
> ...


 
Thanks again for your detailed explanation, labrat!  One of the reason i keep coming back to CPF is this place is full of kind people such as labrat who are willing to share their knowledge with others :thumbsup:


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## divine (Dec 9, 2008)

labrat said:


> A good RCR123 LiIon cell can push out up to 18-19 Amperes!


I hope there is not a rechargeable RCR123 with the protection circuit set higher than 19 amps... or 5 amps.


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## labrat (Dec 9, 2008)

I forgot to clearly state that I mostly use non-protected cells.
Especially when talking about LiIon.
Protected cells should cut off, if the load they connected to started to suck out this amount of Amperes.
NiMh are not made with protection circuitry, as I can find.
A NiMh AA cell would produce up around 10 Amperes.
Maybe more, the NiMh cells I have are a couple of years old, still going strong, but there might be better cells available out there now.
But a 10 Ohm load, connected as shown earlier, would not draw this amount of power!
A short would!
Again, that is why you should not do such testing connected to the cell too long.
Only connect the probes a brief moment to the cell during testing, a second is more than enough.


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## hopkins (Dec 9, 2008)

Sometimes the ideal place to measure the voltage of a cell is inside the gadget
its used to power. Most of the time this is not possible due to limited access.

One solution is if you can measure the current the gadget is drawing from the batteries. Calculate the Resistor value that would simulate that current draw
and then measure the cells voltages outside while loaded by this Resistor where
you can easily get the DMM probes on the cells contacts.


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## edc3 (Dec 19, 2008)

I'm a little confused by this. In this pictures it looks like the DMM leads are touched to the battery terminals and the resistor is placed across the DMM leads. Is this correct? Thanks.



hopkins said:


> putting a load of a 10 ohm resistor (or in that range) on a Nimh cell
> while measuring the voltage gives you a good idea of its 'state of charge'
> 
> approximatly ---- 1.37volts is full ----- 1.16volts is empty and time to recharge.
> ...


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## Badger_Girl (Dec 19, 2008)

yes, that is the same thing as putting the resitor across the battery terminals and then using the DMM to measure the battery voltage across those terminals. 

connecting the resistor directly to the battery terminals or 1 cm up on the DMM leads that are directly on the battery terminals will not make any difference.


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## edc3 (Dec 19, 2008)

Badger_Girl said:


> yes, that is the same thing as putting the resitor across the battery terminals and then using the DMM to measure the battery voltage across those terminals.
> 
> connecting the resistor directly to the battery terminals or 1 cm up on the DMM leads that are directly on the battery terminals will not make any difference.



Thanks Badger_Girl! I found another illustration on Radio Shack's website as well.


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## StarHalo (Mar 10, 2009)

hopkins said:


> One solution is if you can measure the current the gadget is drawing from the batteries. Calculate the Resistor value that would simulate that current draw
> and then measure the cells voltages outside while loaded by this Resistor where
> you can easily get the DMM probes on the cells contacts.



Here are the numbers I'm getting on my 14500-powered light:

4.1 volts
2.25 amps

which works out to:

1.82 ohms @ 9.23 watts

So would this mean the 1 Ohm/10 Watt resistor would work better for me than the 10 Ohm model, or is there some issue I'm missing?

Edit: I can see the amperage would be too high using only 1 Ohm resistance, so the better question is; if I have two 1 Ohm/10 Watt resistors, is there a way I can wire them to provide 2 Ohms (series or parallel)?

EditEdit: It's series. Resistors in series means cumulative Ohms, parallel is reciprocal each + reciprocal total. So two 1 Ohm/10 Watt resistors in series connected to a 14500 would be:

4.1 Volts
2 Ohms
2.05 Amps
8.4 Watts/4.2 Watts per resistor

Using two 1 Ohm resistors is a better deal than using one 2 Ohm because of the high wattage of the circuit, which would be too close to the 10W threshold of a single resistor.


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## NotSoBrightBob (Mar 11, 2009)

Maybe off topic but NICE artwork Hopkins. This is a great community when someone takes this much time and effort to educate a CPF'r. I thank you.

Bob





hopkins said:


> putting a load of a 10 ohm resistor (or in that range) on a Nimh cell
> while measuring the voltage gives you a good idea of its 'state of charge'
> 
> approximatly ---- 1.37volts is full ----- 1.16volts is empty and time to recharge.
> ...


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## StarHalo (Mar 12, 2009)

The Li-Ion/NiMH load testing rig:






Two 1 Ohm/10 Watt resistors in series for a total of 3.0 Ohms tested/displayed.

This circuit tests freshly charged Li-Ion cells at 1.38 amps, and NiMHs at .45 amps (or .91 amps if using only one resistor). 

I don't notice any heat off the resistors if I test a regular Li-Ion for ~3 seconds, but if I leave the pictured LiMN on for ~10 seconds, they do get quite hot (but still well within the Watt rating for each.)

Parts cost:

- Multimeter $3
- Resistor 2-pack $2
- Alligator clips $.60

Total cost: $5.60


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## Russel (Mar 12, 2009)

StarHalo said:


> The Li-Ion/NiMH load testing rig:...


 
I assume that you don't want to use the 200 Ohm scale on the meter. [Edit] Sorry, I see that you were measuring the resistor in the photo. [End edit]


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## Brett80 (Mar 19, 2009)

I am hoping someone would be willing to clarify something about multimeter usage and IMR 18650 cells. I should first say I don't really know how to propoerly use my DMM to measure voltage of my 18650 cells. 

When I test my Sony V 18650 IMR cells I put my multimeter dial on 20V, insert the black probe in the COM socket and insert the red probe in the 10A socket. When I touch the terminals to the cell, I get slight spark from the + terminal and the probe and wires get VERY hot after about 1 or 2 seconds. The display measures randomly fluctuating numbers from .5V to over 6V, which I know can't be right for new cells that should be charged.

Should I use the other 200mA socket on the DMM for the red probe instead? Or is there something basic I am doing wrong?


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## StarHalo (Mar 19, 2009)

Brett80 said:


> Should I use the other 200mA socket on the DMM for the red probe instead? Or is there something basic I am doing wrong?



You should first understand that not knowing how to use your multimeter, especially with LiMN cells, is an excellent way to start a rapid chemical combustion that would create a toxic fire, or what's known as a "vent with flame" event. Here's what it looks like: http://www.youtube.com/watch?v=jjAtBiTSsKY . Now picture that happening in your house, with you leaning over the equipment in your hands.. 

You need to thoroughly learn and understand Li-Ion handling and safety, and then learn proper multimeter use - it's very easy to break either with disastrous results if you don't know what you're doing.

- You cannot check the status of a Li-Ion cell using only a multimeter, you must create a circuit that puts a load on the cell and then measure the working voltage. 

- The 10A plug on the multimeter is for measuring DC amperage, and only below 10 amps. A LiMN cell can easily output 15 amps when shorted, which is more than sufficient to blow the fuse on your meter, if not destroy the meter entirely.

- Shorting a Li-Ion cell is the fastest and easiest way to get it to explode.

If ANY of the above is unclear or uses concepts or terminology you are unfamiliar with, STOP NOW and review any and all information pertaining to Li-Ion handling and/or multimeter use. You are risking severe hazard otherwise.


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## bluepilgrim (Mar 19, 2009)

Keep in mind that a cell has internal resistance, and that when current is flowing through a circuit that the voltage drop across the resisters in series is proportional to the amount of resistance. That means that if there is no load -- no current flowing -- that there is no drop across even the internal resistance, and that's why you can measure full voltage across a functionally dead cell, especially with a digital meter (or old vaccum tube volt meter) which draws very little current. 

That also means you need to test the cell (or battery) under load so you see how much voltage is available to the load including the drop across the internal resistance. If you put a dead short across the cell, all the drop will be across the cell and you'll get a reading of about zero across it and the load -- no current left to go through the meter. (See Ohm's law and series/parallel circuits: if two resistors are in parallel none of the current goes through the one if the other is zero resistance, so there is no voltage drop across the two of them combined, and in the dead-sort situation above the meter is in parallel with the short. I hope I said that so it makes sense.) 
The bottom line is you want to test the cell when putting out about as much current as the actual load will draw. 

Personally, I use a cheap Radio Shack multimeter with a needle for almost everything. For one thing, the reading doesn't jump around as it can with some (many?) digital meters, and that means I can also use to guesstimate capacitance with the ohm meter function by seeing how fast the needle swings to 0 as the capacitor charges up from the meter's battery. I don't need 'digital accuracy' for most things.

EDIT: 
P.S. The internal resistance at a given time is not just one figure, like a carbon resistor would generally be -- it can (expect will) change depending on how much current is drawn.


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## SilverFox (Mar 19, 2009)

Hello Brett,

The problem you are having is that you are measuring amps and you should be measuring volts.

Place the red lead in a socket that allows you to measure volts and you should be good to go.

Make sure the scale is set to a value higher than you want to read, and briefly touch the leads to the battery to make sure you have everything set up correctly. If the meter indicates full scale, or if the leads start to heat up, immediately disconnect and understand that something is not right. 

20 volts is a good setting, now all you have to do is put the red lead in the volt socket. You should be able to check this by changing to measure ohms and hold the black and the red lead together touching each other. You should end up with close to 0 ohms. If you get no reading, you are still not in the right sockets. Be sure to switch back to 20 volts before measuring volts. You can blow a fuse if you measure the resistance of the battery using a volt meter.

The black lead is in the right place.

Tom


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## TakeTheActive (Mar 19, 2009)

SilverFox said:


> ...20 volts is a good setting, now all you have to do is put the red lead in the volt socket. *You should be able to check this by changing to measure ohms and hold the black and the red lead together touching each other. You should end up with close to 0 ohms. If you get no reading, you are still not in the right sockets.* Be sure to switch back to 20 volts before measuring volts. You can blow a fuse if you measure the resistance of the battery using a volt meter.
> 
> The black lead is in the right place...


Or you already blew the safety fuse on the VOM-to-COM (fused) circuit.


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## Mr Happy (Mar 19, 2009)

I think this and other responses have adequately explained that plugging the red lead in the 10 A socket of a multimeter and attempting to measure voltage is a very bad mistake. The 10 A socket is a direct short circuit to the black socket and connecting a short circuit to any kind of unlimited power supply will blow fuses at best, will melt or explode things at worst.

However, a small factual error can be corrected:



StarHalo said:


> - You cannot check the status of a Li-Ion cell using only a multimeter, you must create a circuit that puts a load on the cell and then measure the working voltage.


This is untrue. The status of a Li-ion cell can be estimated very successfully with a direct open-circuit voltage measurement using a multimeter. This forum is full of instructions on how to do this, and every owner of lithium ion cells is advised to own a multimeter and find out how to use it for this purpose.


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## StarHalo (Mar 19, 2009)

*View 1:*


Mr Happy said:


> The status of a Li-ion cell can be estimated very successfully with a direct open-circuit voltage measurement using a multimeter. This forum is full of instructions on how to do this, and every owner of lithium ion cells is advised to own a multimeter and find out how to use it for this purpose.



*View 2:*


labrat said:


> You cannot trust these measurements for LiIon cells.
> 16350 or 18650 cells, I have had a couple of cells that read 4.20 Volts after charging, but the ZTS meter shows no charge, and trying to read any power output from them gives hardly 250 mA output just shorted through the meter!
> They are gone! Empty.Ready for recycling.
> Same goes for NiMh.
> The above mentioned trick with a load resistor is better and more accurate, just don't hook up too long!



Which is correct?


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## SilverFox (Mar 19, 2009)

Hello StarHalo,

With Li-Ion chemistry you can get a very good approximation by reviewing the data presented in post #4 of this thread.

Tom


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## VidPro (Mar 19, 2009)

Or one could say that an AMPmeter (or DMM set to test amps) is basically just a STRAIGHT UP connection direct, with very slight resistance, to test the amperage through that slight resistance.
SO
an AMPmeter test (aka "flash amps") is a DIRECT SHORT, and shorts are not good for batteries, meters or humans.

using a ampmeter to test a total curcuit flow of amps is the right thing to do, having the "curcuit" be both ends of the battery is a dead short, and not a good thing to do.
generally an Ampmeter replaces a WIRE in the curcuit, making (sorta) the same connection as the wire would, straight through.


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## bluepilgrim (Mar 20, 2009)

StarHalo said:


> *View 1:*
> 
> 
> *View 2:*
> ...


 
I'd say both (but I'm not a battery technician or chemist -- so what I think isn't gospel), depending on the condition of the cell. With a good cell, the voltage is a good indicator, but with an old or bad cell the voltage reading may be misleading. I haven't used li-ion cells, but I've worked with lead acid and ni-cad (among others) which also have a low internal resistance because of the chemistry used. 

A car battery, for example, can read over 13 volts but not be able to put out enough current because of high internal resistance (which is a simplified representation of several things going on the battery -- see http://en.wikipedia.org/wiki/Internal_resistance ). You can test a L-A battery with a hydrometer and get a fair indication of charge, but if you bring one to Walmart they use an electronic tester which takes time to run, which seems to charge it while recording the rate of charge, maybe also also doing some discharge testing too. But their machine won't test if a battery can hold a charge over time: it might take a charge and look like it's good but if it sits for a few days you find nothing there and the car won't start. 

You can think of this like water in a tank. The height of the tank determines water pressure -- like voltage. The tank could be almost empty, with little capacity, or the pipe could be too small to give you the amount of water you want, in which case you would see a high water pressure until you tried to draw more than a little at a time, and then you would empty the end of the pipe where you are faster than water would fill the end attached to the tank -- that's like 'internal resistance'. 

So you have voltage, the amps which can be drawn depending on internal resistance, and the capacity (watt-hours or amp-hours) left in the cell, all within within certain times and loads (that's why you need to look at a graph to see what a battery chemistry gives you in performance). Usually you can go by voltage to get an idea of the state of charge, but not always; there are too many factors which can come into play to be sure.


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## bluepilgrim (Mar 20, 2009)

I haven't looked at battery chemistry for decades, so to review, and to understand it better, I looked around on the web. I found a great resource at http://electrochem.cwru.edu/ed/dict.htm 

Check out the links near the top of the page: the encyclopedia, the list at http://electrochem.cwru.edu/estir/ etc. -- there is a huge amount of material available. I found just going throught the dictionary, starting with cell voltage and clicking on hypertext links, to very helpful.


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## DHart (Apr 2, 2009)

*What is the best resistor to test 18650 Li-Ion?*

I understand from this thread that reading open voltage on Li-Ions can give a good general idea of the cells state, providing the cell is in good condition...

But, could one get an even better indication of the cell's state if one were to test the Li-Ion with a resistor across the terminals as shown elsewhere in this thread? 

If so, how do you determine the appropriate resistor specs (ohm & watts) to test an AW protected 16340, or an AW protected 18650, or an AW IMR 18650?


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## Turbo Guy (Apr 2, 2009)

> how do you determine the appropriate resistor specs (ohm & watts) to test an AW protected 16340, or an AW protected 18650, or an AW IMR 18650?


 

http://www.the12volt.com/ohm/page2.asp


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## bluepilgrim (Apr 2, 2009)

I've been looking into this, and it's considerably more complicated than I thuoght it would be. For instance http://www.maxim-ic.com/appnotes.cfm/appnote_number/131

It seems lithium cells have a high internal resistance -- at least the primary cells, and maybe for rechargable lithium ion too -- but I see conflicting information on how much current they can deliver (as opposed to amp-hours or watt-hours). And there are many different chemistries in use, with different characteristics.

I'm still researching, but I would guesstimate and use a resistor which would draw 1 to 3 times the current the light wants, assuming the cell is designed to deliver that rate of current. I would not trust open circuit voltage to be reliable. (But this opinion is open to revision as I continue to learn more about these evil power sources.) 

This can be figured out using Ohm's law and calculating the effective internal resistance, amps, and watts. When you have calculated the watts of a load resistor, multiple that by 3 to 5 times for a safety factor. Get the resistance needed by dividing the volts by the current draw, and getting the current draw by dividing watts by the volts. 
I=E/R and W=EI (I = amps, E = volts, R = ohms, W = watts). Remember that you measure voltage across the cell / load and current through the circuit (but don't put the ammeter -- or the ohmmeter-- directly across the cell since it will likely destroy your multimeter.

Edit: PS .. I found this link http://www.mpoweruk.com/soc.htm which is useful.


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## StarHalo (Apr 2, 2009)

bluepilgrim said:


> I've been looking into this, and it's considerably more complicated than I thuoght it would be.



1. Find the current draw/amperage of your light using the tailcap-off method (DMM set to 10A, one probe on the negative end of the battery, the other on an un-anodized part/lip of the body tube)
2. Divide the voltage of your batteries by the amp measurement - this number is the Ohms resistance/load of your flashlight you want to simulate using a resistor, so -
3. Create the load-test circuit above using the nearest approximate Ohm-rated resistor(s)

My single Li-Ion cell produces 4.1 volts, the tailcap-off current measurement reads 2.25 amps. 

4.1 / 2.25 = 1.82 

My flashlight produces a load of 1.82 Ohms, so that's what I need to simulate with resistors. A pair of 1 Ohm resistors in series gives me a very close 2 Ohms, and that's my completed load test circuit (the added resistance of the wires brings this to 3 Ohms, but that's still very close) I use wire-wound resistors to handle the high wattage.

That's the easy part, the hard part is, does this method produce a more reliable measurement than just testing open voltage..


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## DHart (Apr 2, 2009)

Turboguy... thanks for the link to the calculators. Unfortunately I had no idea what to do when I got there.

StarHalo... thank you for the example... now I know what to do. And good question, you ask, does the resulting data give us any more useful info than doing an open circuit test?


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## bluepilgrim (Apr 2, 2009)

Yes, StarHalo, the hard part...

I just downloaded all the material I could find from http://www.mpoweruk.com/index.htm (site map is http://www.mpoweruk.com/site_map.htm ) and there is quite a bit about lithiums and li-ions, as well as other chemistries -- and there is more on the web, of course. 

Near as I can tell, open circuit voltage is not a good way to find the SOC (state of charge) or the SOH (state of health). I'm confident that testing under load is better, but that won't tell the whole story either. There is a huge amount of information about this, and lithium seems trickier than other cells in this regard. 

http://www.mpoweruk.com/lithiumS.htm
_Measurement of the state of charge of the cell is more complex than for most common cell chemistries. The state of charge is normally extrapolated from a simple measurement of the cell voltage, but the flat discharge characteristic of lithium cells, so desirable for applications, renders it unsuitable as a measure of the state of charge and other more costly techniques such as coulomb counting have to be employed._

And this is complicated by the age and temperature of the cell which cuts off the top end of the capacity even if can discharge down to the low end. Somewhere -- I lost the citation -- it was said it's like having a gas gauge telling the percentage of gas left in the tank but with the tank always getting smaller. so yolu could have a 'full tank' but only a little gas left: the mWh of the cell is diminished. That would happen with other chemistry too, but it would seem that the flatter discharge curve of the lithium would mean the open circuit voltage of a charged battery would not change as much as in a lead acid battery.


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## SilverFox (Apr 2, 2009)

Hello Bluepilgrim,

Keep in mind that the flat discharge characteristic of lithium cells is not so flat at higher loads...

Tom


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## bluepilgrim (Apr 2, 2009)

Ok, Tom, and more complication, but also more reason in my eyes to test under load. 

My understanding of what I read is that a lead acid battery will test lower open circuit when it not charged or old more so than a lithium well (because of the different chemistry). But it has lower internal resistance so the voltage would not drop under load as much as a lithium; it's more sensitive to charge than to current drawn, it looks like. 

But something that throws me is when I look up lithium cells I see 2 dozen chemistries, and it's unclear what is being considered, although the comon primary cells were said to be with manganese dioxide http://en.wikipedia.org/wiki/Lithium_battery . 
Lithium ion rechargables http://en.wikipedia.org/wiki/Lithium_battery add another 4 to Wikipedia's list -- and I guess there are variations in those. Safest bet seems to be to try to find the manufacturer's data sheet and technical information for the cell being used, if available. 

I have bite marks all over me from assuming things over the years. 
http://e-articles.info/e/a/title/The-Lithium-Ion-Battery/ says "
_*Chemistry variations *— During recent years, several types of Li-ion batteries have emerged with only one thing in common — the catchword 'lithium'. Although strikingly similar on the outside, lithium-based batteries can vary widely."_ 

I'm getting overwhelmed at the sheer quantity of information about the varieties of li-ions.


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## SilverFox (Apr 2, 2009)

Hello Bluepilgrim,

Welcome to the wonderful world of batteries... 

Tom


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## Turbo Guy (Apr 3, 2009)

> But something that throws me is when I look up lithium cells I see 2 dozen chemistries, and it's unclear what is being considered, although the comon primary cells were said to be with manganese dioxide


 
and that is a small part of the confusion.

Even if you choose something simple such as.....

NiMH then there are different physical sizes, different, formulations,different sperators,anodes , cathods,casing and ends (caps/buttons). All of this leads to different IR,different heating during charging / discharging,different voltage under load, different,different ,different.

Pb is the same.. Regular old flooded cells starting batteries,hybrid starting / deep cycle, true deep cycle, then there is sealed which includes, Gell and AGM. Then within sealed there are deep cycle,stand by deep cycles which are rated for say 500 cycle ro 60% DOD and ones rated for 1000 cycles to 80% DOD. 

One can study,use,test batteries all of one's life and still be behind the times. To make it even worse there are always new chemistries and improved versions of older chemistries being developed.
A little over 4 years ago LiFePO4 was unknow by most. I have spent untold hours researching, testing using this new chemistry and while many consider me the A123 go to guy I am still learning.


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## DHart (Apr 3, 2009)

Yep, this can easily be all too mind boggling (and too time consuming to try to fully understand) for most of us. 

At least it's very good for the average one among us to know that simple metering measures can easily be misleading. That known, it seems like a good idea to have a number of available cells on hand (rechargeables and primaries), some way of tracking which are older and which are newer... and just enjoy using the lights!


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