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Old Aug 11, 2012, 06:14 AM
Beersmith1000 is offline
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How to test individual cells battery won't charge


Hi
My 8.4v batts won't charge.. Have tried everything but they must be crap cells
I want to break down the 2 packs and maybe make one good one
How can I see which are the good ones?
Please bare in mind there not holding much of a charge
Cheers
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Old Aug 11, 2012, 10:54 AM
flydiver is offline
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In my experience if you have an older used pack with individual cells not functioning properly the rest aren't far behind. If you already don't know how to do cell surgery I'm not sure it's worth the risk. They are cheap now and the process is a bit touchy. I used to do it and don't bother anymore.
Old Aug 11, 2012, 11:17 AM
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More specifics on your packs... Are they NiCd, NiMH, or Lipoly packs?

The easiest way to fix the sort of issue that you're experiencing is with a credit card.
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Old Aug 11, 2012, 11:19 AM
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Sorry there nimh and there new but gotta a refund as there faulty . Just thinking might be able to salvage a good batt out of two
Old Aug 11, 2012, 12:15 PM
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NiMh is even MORE of a problem. If you can isolate a single bad cell in a pack you might be able to replace it...but it's a hassle and outcome is dubious.

Cut the shrink off...they are all soldered together. Voltage alone is not necessarily a good indicator of cell quality in NiXX so finding the bad one(s) is problematic. Best way is unsolder them all, test each cell individually with a decent charge/discharge charger and go from there......see the problem.
Old Aug 11, 2012, 12:25 PM
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How do I do the testing when there individual ?
Old Aug 11, 2012, 12:58 PM
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The easiest way is with a battery analyzer such as the CBA IV.
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Old Aug 11, 2012, 08:19 PM
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Why has no one asked what charger you are using?

Does your charger provide you with individual cell information? If not your first order of business should be to get a quality charger. Also you should have a good wattmeter.

With a quality charger which has discharge capability you can test individual cells. You will have to make up some special test cables to allow you to connect to individual cells via the balance connector.

See here for typical wiring connections:
http://scriptasylum.com/rc_speed/lipo.html

Also here is some excellent reading concerning LiPo batteries:
https://sites.google.com/site/tjingu...arging-how-tos

However the cost of a 2S LiPo is so reasonable as to make it not worthwhile to expend much energy on trying to rebuild a bad pack. But you still need a good charger and a wattmeter.

Glen
Old Aug 12, 2012, 01:18 AM
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I'm with Glen.

Since NiMH do not have taps that allow easy diagnostics / troubleshooting for bad cells, you would be much better served by upgrading to Lipolys, especially given the fact that Lipolys are so cheap these days and offer significant performance improvement and runtime vs. NiMH or NiCd.

Mark
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Old Aug 12, 2012, 04:04 AM
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Ok guys but my budget is very limited .. What's the cost of a lipo charger that's good enough for the job? And will my s controller take it

I have a slash with an x5
Old Aug 12, 2012, 04:06 AM
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It's a vector nx85 charger
Old Aug 12, 2012, 06:11 AM
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Quote:
Originally Posted by Beersmith1000 View Post
Ok guys but my budget is very limited .. What's the cost of a lipo charger that's good enough for the job? And will my s controller take it

I have a slash with an x5
My mistake. I failed to note that you had NiMH batteries not LiPo's. The charger you have is a NiMH charger and is probably OK.

Glen
Old Aug 12, 2012, 06:45 AM
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When I was playing with nicads and nimhs I stuck a straight pin through the covering to check the voltage of the individual cells with a VOM.

Gord.
Old Aug 12, 2012, 04:53 PM
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Ok will try that should there be an obvious voltage difference on the bad cells as there probably not very charged
Old Aug 13, 2012, 06:46 AM
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Before you do anything else, put the battery on a slow charge (charge at 0.1C for 15 to 16 hours) and then test it. As mentioned above, you can use a pin to poke through the insulation to measure the voltage of each cell.


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