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Old 11-27-2007, 09:00 AM   #1
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Default Any way to recondition packs to reduce resistance?

I have several 3800 and 4200 packs that continue to build up resistance with just about every charge. These packs are about a year old, and probably have a 100+ cycles on them. They sat most of the summer outdoor season as I ran LiPo at our club races, but I put a little charge (300-500 seconds) in them and cycled them every 2-3 weeks.

The problem is that they have insane amounts of resistance in them and it keeps growing. I have a Trinity DPD that I usually use for the discharge cycle, but still no help. About a month ago, a couple packs were worthless, but 3-4 had resistance in the 30-40 milli-ohm range on the DPD. Over the last month or so, all but one of these packs has grown to 75-100 milli-ohms of resistance.

Does anyone know of a good way reduce the resistance out of these packs? I've tried 4 phase charges on my CheckPoint charger, 1/10 C charge rates with 1 C discharges, etc., but have had absolutely no luck. Or do you all think these packs are just spent? With a 6.5 in my B44, it spools up like a stock motor []. The voltage and runtime on the packs are still pretty good as several of them have an average pack voltage of 7.15-7.25 on a DPD discharge.

Anyway, if anyone has an idea to salvage the packs and save me some money, I'd appreciate it. I'm wanting to avoid buying any more NiMh cells if possible as more of the places I race allow LiPo all the time, but I still need to have a few NiMh cells that are at least good enough for mod classes at the tracks that don't. I have a used Spintec battery manager on the way, do you think it will do anything?

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Old 11-27-2007, 09:05 AM   #2
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i'm not sure if it works for ni-mh's, or just for memory on ni-cads, but dissasemble the packs, and cycle them a couple of times on a pulse width modulation charger (ask at radioshack for a charger that does alkalines). i can get some capacity back on ni-cads when i do this, so it might work for you.
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Old 11-27-2007, 09:09 AM   #3
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Well when I ran 3800's I discharged charged them down to as close to zero volts a cell and dead shorted them for a few days. Then I would charge them at 6 to 7 amps and then discharge them at 35. One or two of these and the resistance goes down, you loose some runtime, and voltage went up.

Now that was for touring but for offroad I don't really care I just put in a lower wind motor or a higher KV brushless because I can always make more power than the track can handle.
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Old 11-27-2007, 09:44 AM   #4
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wyd, I actually thought about trying that approach since my CheckPoint will deadshort the packs for me. Have you had any problems with cell reversal doing this? That's been my biggest concern about dead-shorting NiMh cells.
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Old 11-27-2007, 12:48 PM   #5
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I wouldn't dead short the 4200s, the spintech battery manager should work though. I am constantly reconditioning other peoples packs for them. I have had good results with the battery manager. People will generally give me their packs when they feel sluggish and are only taking 3700-3800 mah on charge. I cycle them 3-4 times on a battery manager and they are back to taking 4200+ mah and the packs liven up a bit. My own packs are always discharged on the battery manager, then a 10 percent charge put in them. Before charging I put them on a Novak smart tray to .9v per cell. I have packs with over a hundred cycles that still take 4400 mah and run strong. They do fade a bit quicker than new cells, but they are alright for club racing.
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