Amp Draw-Equipment needed and directions how!

[Curious_character]

Sorry Ed, it doesn't work like that. Take a look at the discharge curves of any Li-ion cell in the battery reviews posted elsewhere in this forum. You'll see that:

1. All cell types are different -- voltages drop at different rates as they discharge.
2. Even two cells of the same type are different.
3. The voltage doesn't drop anywhere near linearly as the cell discharges.
4. You can't tell the state of charge by looking at the voltage. You can only make a rough approximation at best.

c_c

 

[IlluminationDomination]

I did not realize there were so many variables.

@ archimedes




There are a bunch of variables in play ...

• how accurate is your DMM-very accurrate

• were they both fully charged and at identical voltage to start-yes

• do both cells have identical chemistry and discharge curves-same chemistry. Not sure about voltage curves. Voltage sag is more prominent on the 4200mAh battery.

• what is the slope of the voltage / SoC curve at that point-I do not know

• how well regulated is your flashlight-I am not sure. It is my first modded light. A U21vn

• are all test conditions (such as temperature) identical-Yes

• etc etc etc

 

[archimedes]

I was just using those as the first examples that came to mind ... my point being mainly that using runtime in a flashlight is not nearly as accurate in measuring the info you want as, say, a battery analyzer.

 

[sbslider]

A problem with measuring flashlight current is that any ammeter drops the voltage, so you're not measuring the current at the actual voltage the flashlight sees when operating normally. Sometimes it doesn't make much difference, but in direct drive lights and a lot of single 18650 cell lights, it can. If you can get sufficient resolution, use the 10A DMM scale rather than a lower current scale. That will reduce the voltage drop. But I made up a meter with even less voltage drop:

The wire is about 7 inches of #22 copper wire connected, as you can see, directly between the probe tips. The probes go to an inexpensive DMM set to the lowest mV scale. Connect the probes to the device under test like you would for any current measurement. The scale factor is 10mV/amp, or 100mA/mV. This is a smaller drop than a typical DMM but of course the resolution isn't adequate for low current measurements. If you do something similar, make sure the wires solidly connect right at the probe tips. You can use a measured voltage and known resistance to adjust the exact wire length (for example, 5.0 volts and a 5 ohm resistor which should measure 10mV for the 1A that's flowing).

c_c

This approach is brilliant, nice work!!

 

[IlluminationDomination]

It looks like the Amp draw test did something to my Etech DMM!

Ever since I did numerous Amp draw tests the dial and some internal mechanism are not in sync. When I go to the desired setting the LCD screen is either blank or it reads Zeros like it should but when I touch the probes NOTHING happens,no numbers register. I have to keep playing with the dial and eventually I can get it to work.

I bought it in January 2013. I guess it is time for another one. I do not have the knowledge like some of you guys that could probably fix it. Then again, they are only $20/$25 for a half decent one.

 

[IlluminationDomination]

Here is a picture of it.

 

[IlluminationDomination]

Checked the Fuse. It was blown. Put a new one in, same symptoms...buying a new one.

 

[IlluminationDomination]

It looks like the Amp draw test did something to my Etech DMM!

Ever since I did numerous Amp draw tests the dial and some internal mechanism are not in sync. When I go to the desired setting the LCD screen is either blank or it reads Zeros like it should but when I touch the probes NOTHING happens,no numbers register. I have to keep playing with the dial and eventually I can get it to work.

I bought it in January 2013. I guess it is time for another one. I do not have the knowledge like some of you guys that could probably fix it. Then again, they are only $20/$25 for a half decent one.

I believe I figured it out.

In my NEW Innova 3320 DMM it states in the manual:

*10.00A

*A waiting period of at least 15 minutes is necessary between every15 second testing period.

I guess holding the leads down for 20 to 30 seconds for some of my tests [when the numbers were racing back and forth] must have fried or damaged some of the internal parts!!!


I WONDER if they mean a single test 15 consecutive seconds or would testing numerous amp draws in increments of a few seconds be OK?

 

[HKJ]

There is not really anything that can be damaged on the 10A range. Running at to high current will heat the shunt (A thick wire) and it may change resistance a bit, i.e. the meter would be slight off in the readings. At worst the solder holding the wire would melt
In the above I am not talking about using it on really high current circuits, then much worse can happen (Like explosions).

I have looked at the meter here: https://lygte-info.dk/review/DMMInnova3320 UK.html there is also photos of the inside where the thick wire can be seen.

You can try taking the circuit board out and clean the golden tracks (Range switch) on the other side with isopropyl alcohol, this operation is a bit delicate, but may salvage the meter (Check my photos first, then you will have a good idea about what it requires).

 

[IlluminationDomination]

There is not really anything that can be damaged on the 10A range. Running at to high current will heat the shunt (A thick wire) and it may change resistance a bit, i.e. the meter would be slight off in the readings. At worst the solder holding the wire would melt
In the above I am not talking about using it on really high current circuits, then much worse can happen (Like explosions).

I have looked at the meter here: https://lygte-info.dk/review/DMMInnova3320 UK.html there is also photos of the inside where the thick wire can be seen.

You can try taking the circuit board out and clean the golden tracks (Range switch) on the other side with isopropyl alcohol, this operation is a bit delicate, but may salvage the meter (Check my photos first, then you will have a good idea about what it requires).

Thank You. The ETEK[YELLOW DMM] is the one that is 5 years old and damaged/inconsistent in its operation.

My NEW INNOVA is NOT the one with the issue. In fact it will not arrive until Monday!

Sorry If I confused you with my example by using the INNOVA'S user manual to guess as to why the dial on my Etek will work sometimes and other times no display and no voltage read outs.

 

[IlluminationDomination]

@HKJ

The statement below is in your review.

(But watch out for the mA range, a battery in that range will blow the fuse).

Are you talking about the RED lettered selection 10 MegOhm input DCV? OR the AC -mA range?

I think your answer was clear but I want to make sure!

Thanks,,,,,,,,,,Ed

 

[HKJ]

@HKJ

The statement below is in your review.

(But watch out for the mA range, a battery in that range will blow the fuse).

Are you talking about the RED lettered selection 10 MegOhm input DCV? OR the AC -mA range?

I think your answer was clear but I want to make sure!

I am talking about when you are measuring batteries, if you turn the switch past the battery ranges into the mA range with the battery connected, you will have to replace the fuse.

 

[IlluminationDomination]

I am talking about when you are measuring batteries, if you turn the switch past the battery ranges into the mA range with the battery connected, you will have to replace the fuse.

Thanks,,,,,,,,,,,,I will stay away from the AC mA if that also applies. However, it is 3 clicks away from the DCV[Auto ranging selection]

I will especially stay away from the DC mA range which borders the "Battery Load Test" Selection[1.5V/6V/9V and 12V].I suspect your suggestion was based on this scenario!

For this reason and others that may cause the fuse to blow I ordered 5 X GMA 315mA[.315A]/250V Fuses that the manual stated in the specs.

Thanks again for your help.

 

[HKJ]

Thanks,,,,,,,,,,,,I will stay away from the AC mA if that also applies.

It do, but as you say it is farther away from any dangerous positions on the range switch (ACV to ACmA is two steps).
I did blow the fuse while checking the battery tester, I was switching back and forth between the different test ranges and suddenly they stopped working, because I had switched to far once.