NIMH battery problem - half of cells warm, low power

[paul]

Hi Guys,
I have a 5000mah duratrax nimh stick that has been having some problems. It didn't seem like it was holding a charge anymore, but went through a full charging cycle at 4.5 amps yesterday. Today when I ran it, it didn't seem to be putting out the power that it should have been. I stopped after about 4 or 5 minutes of running and noticed that only the negative end cell was noticeably hot. The 2 beside it were a little warm too, but the end was distinctly hotter.

I took off the shrink wrap, and I don't see anything visibly wrong such as corrosion, leakage, loose tabs, etc.

So what could the problem be, and is it fixable? I'm thinking that maybe just because it's a Durtrax battery that maybe it's junk. Voltage when charge finished was around 8v (maybe a little over), it's now at 7.5v. Thanks for any help.

[Eau Rouge]

NiMh are notoriously fickle and fragile. They like to be used (charged and discharged) regularly. They hate to sit stagnant for long periods of time. They lose capacity, power and everything else very easily. Sometimes they need to be "woken up" to perform well, sometimes they are just flat and dead. Cheaper packs have a higher chance of this happening than more expensive matched race packs.


Here's what I would do...

Let the pack cool completely.
Charge the pack at a very low amp rate and build up the charge slowly (like 1 amp)
Discharge the pack on a 20-30a discharger
Balance the cells (all cells with the same discharge voltage)
Let the pack cool completely.
Charge the pack normally (4-6 amps, depending on the type of cell and capacity)

If you don't have a discharger or cell balancer, try this:

Let the pack cool completely.
Charge the pack at a low amp rate and build the charge slowly (like 1 amp)
Run the pack down in the car
Let the pack cool completely.
Charge the pack again at your normal amp rate, depending on the cell type

You should have a good chunk of the performance back into the pack, if you are lucky. If a cell went bad, you'll know it when you run it again and it's time to change to LiPos.




dc

[paul]

NiMh are notoriously fickle and fragile. They like to be used (charged and discharged) regularly. They hate to sit stagnant for long periods of time. They lose capacity, power and everything else very easily. Sometimes they need to be "woken up" to perform well, sometimes they are just flat and dead. Cheaper packs have a higher chance of this happening than more expensive matched race packs.


Here's what I would do...

Let the pack cool completely.
Charge the pack at a very low amp rate and build up the charge slowly (like 1 amp)
Discharge the pack on a 20-30a discharger
Balance the cells (all cells with the same discharge voltage)
Let the pack cool completely.
Charge the pack normally (4-6 amps, depending on the type of cell and capacity)

If you don't have a discharger or cell balancer, try this:

Let the pack cool completely.
Charge the pack at a low amp rate and build the charge slowly (like 1 amp)
Run the pack down in the car
Let the pack cool completely.
Charge the pack again at your normal amp rate, depending on the cell type

You should have a good chunk of the performance back into the pack, if you are lucky. If a cell went bad, you'll know it when you run it again and it's time to change to LiPos.




dc

Thanks a LOT for the info! Unfortunately, I do not have a balancer or discharger, so I'll follow the second set of instructions. This battery has only been cycled at most 30 times (probably more like 20). I just bought it in spring, and have 2 others that I cycle in/out. I'll report back with results in a day or two.

Oh, and I have thought about lipos, but the extra expensive is what has held me back at the moment.

[Eau Rouge]

Extra initial expense. Long run, they cost a lot less, because after 30 cycles, you aren't worried about where you should take them to dispose of them properly.

[paul]

Extra initial expense. Long run, they cost a lot less, because after 30 cycles, you aren't worried about where you should take them to dispose of them properly.

Very true! I'm sure the brushless systems in my b4.1 and boomerang would really appreciate the upgrade too

Probably not until next summer though...
in about a month or so my backyard bashing season will be at an end