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Old Feb 26, 2002, 08:12 AM
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Steven9026's Avatar
Lexington, South Carolina
Joined Oct 2001
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Testing Battery For Mah Capacity

Hello,
How do you test a single battery to determine it's MAH capacity?
I have several batteries that came out of some old packs that I found, but they are not marked with the MAH capacity.

Thanks,
Steven
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Old Feb 26, 2002, 08:44 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
Cycle them with a charger that can work with individual cells..
Now you start to see why we recommend you start with the best charger you can afford.. needs change over time..
..a
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Old Feb 26, 2002, 08:50 AM
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Lexington, South Carolina
Joined Oct 2001
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Andy,
I'm using a Tekin BC112 C charger. I can do a single cell charge, so how do I go about determining the Mah of the cell? I should know this, but I'm having a brain fart I guess.

Steven
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Old Feb 26, 2002, 10:09 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
You do a single-cell discharge also..
My I2 can do it, don't know anything about that charger, but if it can cycle, it should do the job..
..a
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Old Feb 26, 2002, 11:22 AM
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Poor Man's Capacity Measurement

Well, if you have a good DVM, some electronics experience, and LOTS of free time, then you can make a poor man's discharge acquisition system. It can give approx mAH values:

(1) Take a wild guess at the cell's capacity. Don't worry about being wrong, but attempt to nail it as close as possible.

(2) Charge the cell at a C/10 rate (per your guess) for 14-16 hours. Second best is to use a quick charger set to single cell mode.

(3) Divide the guessed capacity by 5 (C/5). This will be your discharge rate. For example, a 600mAH cell will be discharged at 120mA.

(4) Choose a resistive load that provides the C/5 current draw. A 3V flashlight bulb makes a good load. It does not have to be exactly C/5. But you must record the load current for later use.

(5) Continue discharging until your cell measures exactly 1.0VDC. The voltage monitoring will require you to check every 5-10 minutes. When the voltage is met, then record the number of hours it took. Re-measure the current draw at the lower voltage.

(6) Calculate the average load current: mA = (Current1 + Current2) / 2.

(7) Calculate mAH: mAH = mA X Hours.

After doing this once or twice I expect that you will decide that those unmarked cells are best used in the kids' toys.
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Old Feb 26, 2002, 11:27 AM
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Lexington, South Carolina
Joined Oct 2001
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Thanks for all the info. I'll try charging them at a C1 or maybe even half that and see what happens. I thought there may be an easy way to do it , that I was aware of.

Steven
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