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Old 09-16-2012, 02:54 PM   #1
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reviving nimh packs

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Hi everyone,

I have a relatively new Sanyo 2700 mah 6V pack and it got accidentally drained (bumped the switch to on)...I've tried cycling it many times now on my Triton charger, but it will only take about 1100 mah at 6.8 - 6.9V. I was reading that you can "zap" the pack with a 12V source for a couple of zaps to revive the pack and recharge. Has anyone done this before and is it safe? I really don't want to throw this pack away unless I absolutely have to. Thanks for any input.

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Old 09-16-2012, 03:14 PM   #2
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Re: reviving nimh packs

As the number of cycles increase "Fingers" in the electrolyte grow between the electrodes, affecting capacity and eventually shorting them out. The purpose of hitting them with the higher voltage is to burn those fingers out and sometimes revive a shorted cell. This process should be done to each individual cell.

The problems are many. First is the possibility of damaging the cell completely and in any case you will only minimally reduce that growth. Even if the cell increases in capacity or removes a short, I find the life expectancy is seriously reduced and not worth risking any aircraft over. In not much time the finger growth can short the cell again. Finally, the current output may be severely degraded and the pack can sag if even a moderate load is placed on it.

However, if yours is low time and still suffering then you may be able to check each cell voltage individually for one that may be much lower than the rest and pulling the pack down. If that is the case then really the only option would be to remove that cell and run it as a 4 cell pack.

Either way, when I find a pack suffering I relegate it to the role of test source only, used for systems checking and rigging. As I stated before it is not worth trying to fly with it.
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Old 09-16-2012, 04:17 PM   #3
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Re: reviving nimh packs

check your settings on the charger. You might have a safety setting that will allow the pack to only charge to the 1100 mah and then the charger will stop. What are your discharges like for mah.

Also ensure you have it set for a 5 cell pack as well.
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Old 09-16-2012, 04:41 PM   #4
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Re: reviving nimh packs

I have done the same thing and no matter what you do it will not take a full charge.
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Old 09-16-2012, 06:30 PM   #5
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Re: reviving nimh packs

After a certain point the more you cycle a pack the worse the capacity gets. I have found that charging nimh packs at 1/20 of their capacity is best. When using 1/10 they get too hot when full. And the old 50 ma charger will not fill them. I have also found that after a rest of an hour or so after charge that 1.38 V per cell is full, note that these cells will reach that voltage long before they are full.

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Old 09-16-2012, 08:39 PM   #6
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Re: reviving nimh packs

Along the lines of what Kip says but charge at the lowest possible rate that your charger can deliver. A battery manufacturer gave me this advice after reviving some cells with the caution that they were then only good for 90% of their design capacity. Regrettably any type of abuse seems to shorten their life - been there, done that.

Then test it through a normal discharge / charge cycle(s) before you use it remembering Cougar's good advice which is along the lines of "if you subsequently trash a plane or cause others harm what would your decision look like looking back ............?".

There are other uses for batteries that are suspect like some posters mentioned plus things like smoke systems or bomb drops ............................

Good luck.
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