Pack get HOT when charging
 

I just bought an OFNA DC Pro Charger and I've charged 2 packs with it and they both got very hot before the charge finished. The first pack I caught as it was getting ready to finish and noticed how hot it was so I stopped it a little short. The second finished and was very hot, at least to me.

I was charging 3300mAh NiMH packs at 5.0 amps.

Am I doing something wrong? Should the packs be so hot when they finish charging?

I've read of a temperature sensor for the pack. Is this necessary?

Anyone else have this charger? Anyone one else use the temperature sensor?

Thanks, Mike

If I remember right 140*F is the max temp they should get when finished. Anywere from 100*-120*F Is normal.
A temp sesor is a good idea when charging NiMh packs, or just keep temping them with a temp gun

NiMh should peak at 125-130F - any hotter and the charge rate is too high and you're shortening the life of the pack by getting it that hot. For a new 3300s, charge at 3.3amps - that should lower temps to proper range, starting out at 5amps is a little high unless you're racing and don't care what kind of cycle like you're going to get - it won't be long starting out that high.

After 5 maybe 10runs, bump the rate to 4amps and see what the temp is like (I use an IR gun on my pacs). If its OK, run them another 5 or 10 times and them bump to 5amp and check temps.

You can get these hot enough on the charger to make them vent or actually blow up, so be careful if they're getting real hot. You should be able to hold them, if you can't they're getting too hot. Once a cell vents, its pretty much ruined and it needs to be replaced.

Thanks, that's the kind of info I was looking for. I didn't have any idea they would need to be "broken in". I thought they would accept a charge rate of well over 1C, I really thought 2C wouldn't be a problem. I guess I was wrong about that.

I've seen brand new pacs ruined in less than 5 charges by using too high of a charge rate. Overheating will destroy them a lot like over heating will demag a motor.

This is intended for their own packs, but its good advice on pretty much any stick pack. I would not be in a rush to bump the charge rate up due to concern about overheating (realize this was written for 4200 and 4600 pacs) -

http://www.promatchracing.com/stickpackins.php


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