NiMH packs getting hot
05-28-2005, 12:31 AM
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NiMH packs getting hot
I'm sure everyone here reading this now has seen this question and maybe even answered it a few hundred times, but here goes. I have just recently bought a couple of 2000 mah NiMH packs for a new big plane I have just finished. I am not familiar with NiMH (only NiCad) and don't have a lot of experience with bigger battery packs. I have the Accu-Cycle Elite. I have burried my battery pack inside my Cap 232 and want to charge it, while it is inside the airplane (have a charge jack in the switch harness) and I'm worried about all of this talk about NiMH battery packs getting hot. What amp rate can I charge at and not have a problem or is the issue larger than that? Any advice would be much appreciated. Thank you.
05-28-2005, 06:16 AM
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RE: NiMH packs getting hot
DownSideUp
I use Ni-MH for all my flight packs. "Hot" is a relative term. Yes, NI-MH will often feel warm to the touch after a rapid charge. So will Ni-Cad. On my NI-MH packs I never exceed C/2. Ie, on a 2000MAh pack, 1A. I don't like to mount my flight packs deep inside a plane, personal preference. I mount them where is can reach in and feel the packs. Additionally, I replace the pack sheath with transparent shrink. This allows visual inspection as well. If there is any powdery deposit around the posistive end of any cell you know that the pack is busy dying. The deposit is leaked electrolyte and will be a sign of possible overcharge or other abuse.
Safe Flying!
I use Ni-MH for all my flight packs. "Hot" is a relative term. Yes, NI-MH will often feel warm to the touch after a rapid charge. So will Ni-Cad. On my NI-MH packs I never exceed C/2. Ie, on a 2000MAh pack, 1A. I don't like to mount my flight packs deep inside a plane, personal preference. I mount them where is can reach in and feel the packs. Additionally, I replace the pack sheath with transparent shrink. This allows visual inspection as well. If there is any powdery deposit around the posistive end of any cell you know that the pack is busy dying. The deposit is leaked electrolyte and will be a sign of possible overcharge or other abuse.
Safe Flying!
05-28-2005, 06:39 AM
#3
RE: NiMH packs getting hot
You'll have to baby sit the charge cycle during rapid charging cycles. If it seems like it took longer than normal, and you will know because you charged them 20 times before, it might have missed the peak. That can happen now and then with chargers but my Elite has never missed a peak yet. If it's taking longer than normal just stop the charge cycle. Measure the voltage under load and if ok, go flying.
It's better to be able to feel you batteries temperature but in your case just pay attention to how long it's charging (never leave them while they are charging). So the only way they can get hot is if they are overcharged with a higher rate than slow charge. Also if you slow charge you batteries all the time they will never get hot, just a little warm. I'm a firm believer in slow charging as much as possible. Fast charging will decrease battery life and can cause one cell to go low if you don't discharge them and slow charge them every 5 cycles.
For my new 1950 mah NiMh pack, they said to slow charge at 200 ma for 14-16 hours (for a fully discharged battery). Theoretically it should only take 10 hours at C/10 but I think they add more due to internal losses and charging inefficiencies. So if you setup your pack to charge at this rate (C/10 or 200 ma = 0.20 amps) you will be fine, it will NEVER get hot. In fact I just programmed my Elite for this exact setup. It's been charging all night and is almost done with its formation charge.
It's better to be able to feel you batteries temperature but in your case just pay attention to how long it's charging (never leave them while they are charging). So the only way they can get hot is if they are overcharged with a higher rate than slow charge. Also if you slow charge you batteries all the time they will never get hot, just a little warm. I'm a firm believer in slow charging as much as possible. Fast charging will decrease battery life and can cause one cell to go low if you don't discharge them and slow charge them every 5 cycles.
For my new 1950 mah NiMh pack, they said to slow charge at 200 ma for 14-16 hours (for a fully discharged battery). Theoretically it should only take 10 hours at C/10 but I think they add more due to internal losses and charging inefficiencies. So if you setup your pack to charge at this rate (C/10 or 200 ma = 0.20 amps) you will be fine, it will NEVER get hot. In fact I just programmed my Elite for this exact setup. It's been charging all night and is almost done with its formation charge.
