NiMh packs got so hot, the wrap melted!
07-12-2008, 09:50 PM
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NiMh packs got so hot, the wrap melted!
I've been running my Evader ST on a Mamba Max ESC with a 6900kv motor. The batteries I have been using are fairly new 6cell 7.2v 3300 and 3600 mAh nimh packs. So far, I've had 2 packs get so hot that I cannot hold them for more than 3 seconds and the wrap around them has melted to the point it tore (at the connector end). All of my packs, ESC and charger are using Deans connectors so no probs with heat there. Anyone have an idea why these packs could be overheating so badly?
07-12-2008, 11:01 PM
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RE: NiMh packs got so hot, the wrap melted!
I have done the same to a Venom 3600 pack. After taking it all apart and trying to test the cells I have found one that only holds 1100 mAh. I'm pretty sure this one was very hot. Probably going into cell reversal during discharge. The others I have tested (I'm not finished) have been in the 2300-2600 mAh range. I am assuming this in an older battery pack that I have, or just plain abused.
You need a charger that tells you how many mAh it is charging to find these things out. You also need a way to discharge the batteries individually down to 0.9 volts. Then charge them slowly and see how much power goes back into them. Some suggest matching cells with a high discharge rate and reading how many mAh come out of the battery when fully charged with a slow charger. This sounds like a good idea, but requires more hardware. A high quality charger can do both, even automatically and keep the results for you to review later.
I think the larger brushless motors pull too much amperage for NiMH packs. Perhaps really good lower resistance packs are better, but I don't have any. I am new to this, but it is what I have observed. A good lipo will not get hot, supply plenty of wattage and weigh less, which will makes everything run cooler. I plan on switching soon to lipo for these reasons.
You need a charger that tells you how many mAh it is charging to find these things out. You also need a way to discharge the batteries individually down to 0.9 volts. Then charge them slowly and see how much power goes back into them. Some suggest matching cells with a high discharge rate and reading how many mAh come out of the battery when fully charged with a slow charger. This sounds like a good idea, but requires more hardware. A high quality charger can do both, even automatically and keep the results for you to review later.
I think the larger brushless motors pull too much amperage for NiMH packs. Perhaps really good lower resistance packs are better, but I don't have any. I am new to this, but it is what I have observed. A good lipo will not get hot, supply plenty of wattage and weigh less, which will makes everything run cooler. I plan on switching soon to lipo for these reasons.
07-29-2008, 10:46 PM
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RE: NiMh packs got so hot, the wrap melted!
I'm switching soon as well. I'm just getting tired of the hassle with these nimh's on my MM6900 system...it's burning them up! I have an Apache 2500 charger, I just need to figure out a way to get power to it without spending a great deal of money. I have a 350w Antec PSU from my old computer...but I'm not sure what to do with it.
