Reviving old NiMH??

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Old 09-08-2010, 04:05 PM
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Default Reviving old NiMH??

I'm trying to revive some old NiMH packs that have been sitting for several years. The packs were in great shape before they went into storage, so I'm holding out hope that I can still get some use out of them, but they keep false peaking.

I've got my charger set at 5.0 amps and the delta peak at 4 mV. Any recommendations on charger settings? I also have a 20 amp discharger I can use to cycle the packs if need be.

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Old 09-08-2010, 05:43 PM
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Slow charge them at 1/10c (500mah for a 5000mah pack) for 12 - 15 hours

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Old 09-08-2010, 08:36 PM
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Depending on the stage of deterioration, nickle cells can be brought back in a few different ways. First, I would simply crank up the peak mv and keep an eye on the pack so you can stop it yourself. If it works, you would simply want to manually stop the charge process once the pack has reached 125F. If it does not work, you will just keep false peaking and other methods must be used. After a few cycles the pack should work correctly with 4-5mv cutoff. Remember that you must stop the process yourself if you turn up the peak detection, or you risk overcharging the pack. Other than that you will not do any harm by turning up the peak mv.

Charging at 1/10C for 12-15 hours is probably the most common method, because it seems to work and it is safest. Again, you will likely need to turn up your peak detection, but at the ultra slow charge rate there is no risk of overcharging, since the pack can bleed off excess as heat faster than the charger is supplying it. The pack could be warm by the 3rd hour, but you should give it full time to equalize the cells.

A method that I like is what I call "zapping" them. It is extremely dangerous, stupid and could seriously injure someone, so I do not recommend it unless you are comfortable with the possible outcomes. But this method has given me extra packs when I couldn't afford new ones. I disassemble the packs and "zap" each cell, one at a time, with 20A 12V, for just a moment at a time until the cell reaches appx. 100F. Then cycle the cell as usual and measure its output. I have had cells explode nearly instantly, and I have had some that still didnt work, but I have had several packs worth of cells come out much better. This is obviously a desperate attempt, but it can yield good results if you have no other choice.

Back when I was a starving young adult I would raid the battery recycling bins at Home Depot and Lowes and make awesome packs from seemingly dead cells. I even came out with a few homemade "matched" packs that performed better than some of my friends $80 "matched" packs. I recommend going Lipo if you can, but if not I would try the first two methods. If they dont work I highly recommend buying new packs, unless you are crazy and broke like I was back then.
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Old 09-08-2010, 08:57 PM
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Awesome. Thanks guys for responding. Think I'll try the safe options! I'll probably end up buying some LiPo's anyway, just wanted to salvage what were at one time some very nice matched packs. I know they're no longer race worthy, but I'm sure I can still get some use out of them.

One more question, after connecting all four packs to my charger, three of them false peaked as I described in the original post. The fourth pack wasn't even detected by the charger. It was like it wasn't connected. I tried connecting through the Deans plug and also used alligator clips to circumvent the plug, but no luck. Is it possible that a cell in that pack has completely lost its ability to even pass current? I'm almost certain that all the connections are solid throughout the pack, so I don't think it's as simple as a loose battery bar or something like that.
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Old 09-09-2010, 12:12 PM
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When the cells sit for too long without any cycling, the internal resistance skyrockets. Most quality chargers will not be able to recognize the pack once it gets too high. Luckily this can often be (somewhat) reversed with a forced charge. Another option I did not mention was a wall type trickle charger, such as what comes with many RTR vehicles, is basically the same as a very low setting on your charger with no peak detection. The difference is that these wall type chargers do not recognize a problem and will charge anyways. This is whats needed to "wake up" most dead packs. If you have one lying around, anything from 0.1A to 0.5A, you can hook it up and leave it for several hours, then discharge it hard, then your main charger should pick it up.
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Old 09-09-2010, 02:39 PM
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Best of luck with your revival. I've had mixed results doing the same thing, but enough positive results to make it worthwhile pursuing. The only thing I've found is some of my revived packs self discharge at very increased rates, like 72-96hrs and they're discharged and need to be recharged. ll of mine seem to have increased self discharge thoiugh, just some much more than others.


You left out that one method with the automobile batt charger.....hehehe
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Old 09-09-2010, 05:23 PM
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Originally Posted by Duster_360 View Post

You left out that one method with the automobile batt charger.....hehehe
Thats the 12V 20A method I have used. Dangerous as hell but flat out amazing results. But with todays lipo prices I see no need to endanger my health over Nimh batteries. When a Sub-C cell goes off it is not something you want to be near.
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