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Old 20th May 2010, 09:17 AM   #1
Odomus is offline Odomus  United States
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Unhappy mAh Testing... finding out...

I have a slight problem I have certin batteries, that dont show the mAh... some NiCd, MH etc... Is there a formula, or something that I can use to actually test to get the appropreate value?

I have a MulitMeter, so I can get any values I can... but I cant figure out how to get the mAh.

It shouldnt matter the voltage I figure... so anyone know how to get the mAh out of a battery?
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Old 20th May 2010, 11:27 AM   #2
AndrewT is offline AndrewT  Scotland
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try a jFET CCS set to ~10mA (2sk170gr or bl)
charge the battery and measure how many hours it can supply till the voltage drops to 1.1Vdc.
Multiply the mA * hours to get mAhrs
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Old 20th May 2010, 03:26 PM   #3
stoc005 is offline stoc005  United States
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Weigh them. Compare them to other cells that are the same size/weight and you will have an approximation of their capacity. How accurate are you trying to get their capacity?? If the cells are old, they are probably less than their rated capacity.
1. Charge 14-16 hours at 10%, constant current, of the rated capacity. Battery MUST be fully charged. Use a peak charger if you have one.
2. Discharge at 10% of the rated capacity using a constant current load. Measure the time it takes to get to 0.9 volts per cell, assuming ni-cad battery chemistry.
3. Multiply the constant current load value, in milliamps, by the discharge time in hours and you will get the ma-hours capacity of the battery.
4. Repeat 1-->3 this until the answer you get is the same each time. Ni-cads typically will measure less than rated capacity the first time if they have been sitting around not being used much. The best thing you can do for ni-cads is use them frequently, charge them when they are discharged, and do not abuse them too much.
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Old 20th May 2010, 05:44 PM   #4
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the mAH rating is usually on the manufacture's website.

For charging I use MAX713
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Old 20th May 2010, 06:07 PM   #5
Odomus is offline Odomus  United States
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Thank you for all the ideas, and help guys... Iam using the first idea though... since I have all the parts, and I can rig one up quick. So as soon as I get home I will do it.

Oh and BTW when the batteries dont have wrappers on them anymore, and all you remember is that they were nicd or nimh... kinda well, doesnt help.... if you can tell me the manufact from a naked battery I would love to know how.

My Charger isnt the problem, I have so many.... so it doesnt bother me, just would like to know the general mAh is all.... which doesnt mean much on the charging....but thank you I appreciate it.

Would be cool if someone would make a digital thing reader to auto tell you the mAh... instead of using math, and such. Oh well one day you never know.

Thank you all I appreciate all the help.
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Old 20th May 2010, 07:30 PM   #6
stoc005 is offline stoc005  United States
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Default Try these....

Hobbico Accu-Cycle Elite
TowerHobbies.com | Great Planes ElectriFly Triton2 DC Computer Charger

Either one of these computer battery charger/dischargers will tell you exactly the Ma-hour rating of your batteries. They will work with all kinds of battery chemistries, Ni-cad, NiMH, Li-Po, lead-acid. 1 to 28 cells in series.

I fly electric RC planes with Li-po batteries and have dealt with Ni-cads for years as well.
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Old 20th May 2010, 07:44 PM   #7
Odomus is offline Odomus  United States
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Well I just bought the Red and silver one, it looked cooler heh.
That is all I needed... thank you so much... hopefully I will get it soon.

I appreciate al the help guys this is going to come in handy thank you so much.
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