Maha C9000 battery cooker...

Let's start by saying I've had great results with two Maha C9000 chargers I have. They've run though countless cycles. Today I put in four 2000mAH tested AA in for a standard 1/0.5a charge/discharge refresh cycle. After about 2 hours the batteries became super hot and all measured 65-70c. Stopped the charge, let things cool and tried again. I've since put a fan on this one but the question is, has anyone had a C9000 cook cells? I'd sooner think my BC900 would do so (that's why I have the fan in case) than the C9000.

The resistance voltage measure for these batts rang in 1.7-1.9 by the way. Not terrible and certainly not battery cooking bad...

The batteries were probably in a 20 perc state of charge or so when first put in.
___________
Posted from my phone.

...and it is a bad practice to put a fan in any charging equipment which utilizes temperature as a termination method. I have read around here that it also affects the primary termination method of dV/dt (causes missed terminations). My batteries with IRC around 1.8-1.9 also get hot (not sure if they get at the 65-70C range) since the higher resistance of cells produce more heat at 1A rate so it might be normal what you get, but a fan will definitely make things worse.

I recently got a BC-700 and a C9000 and I'm fiddling with stuff now. I've got a laser beam thermometer and the highest I've read, on either, is ~126* on the two inner bays. The BC-700 has gone into thermal shutdown on only a 700 mA charge with some AccuPower 2900s, but came back on after they cooled.

Kind of interesting.

For the record, I'm not standing there through the 38 hour break ins, monitoring temps every 10 minutes, just something I've toyed with and noticed.

Chris

this wont happen with eneloop cells

apagogeas said:

...and it is a bad practice to put a fan in any charging equipment which utilizes temperature as a termination method. I have read around here that it also affects the primary termination method of dV/dt (causes missed terminations). My batteries with IRC around 1.8-1.9 also get hot (not sure if they get at the 65-70C range) since the higher resistance of cells produce more heat at 1A rate so it might be normal what you get, but a fan will definitely make things worse.

Click to expand...

I'll keep that in mind then about the fan. Never have I had the Maha do this before. Was pretty strange to me.


___________
Posted from my phone.

The problem is caused by crap batteries. If you tell the charger to force 1 A into a crap battery it will obey your instructions. If the battery gets hot when the charger is simply doing what you told it to do it's not the charger's fault. The solution here is to use a lower charge rate like 0.5 A. Or just let the batteries get hot until the charger stops automatically. Unless the batteries get so hot they are making a horrible smell and melting their covers they are not getting too hot. You should perhaps think about retiring those batteries and getting some eneloops.

I have seen some NiMH batteries (AA) that state on the label to charge at not more 300 mA. These might be batteries for solar powered lights but at any rate they would probably get quite hot in a charger.

Mr Happy said:

The problem is caused by crap batteries. If you tell the charger to force 1 A into a crap battery it will obey your instructions. If the battery gets hot when the charger is simply doing what you told it to do it's not the charger's fault. The solution here is to use a lower charge rate like 0.5 A. Or just let the batteries get hot until the charger stops automatically. Unless the batteries get so hot they are making a horrible smell and melting their covers they are not getting too hot. You should perhaps think about retiring those batteries and getting some eneloops.

Click to expand...

It's the chargers fault if it's still going when the surface temperature of the batts are measuring 70 deg C. and it's still going, yes? Is 158f not enough to trigger a thermal shutoff?

Using only this page for reference it appears the C9000 has a cutoff of 135f...

http://www.fatwallet.com/forums/deal-discussion/881250/

Two of these are year old AA Eneloops by the way folks. Two are regular Sanyo 2700 AA Nimh.


___________
Posted from my phone.

Something wrong with your charger(s) and/or cells then. My AA Eneloops (even my almost three year old ones) hardly get warm charging at 1000mA on my C9000s.

Does the C9000 have a thermal shut-off? (thermal sensor, regulation, ..)

in the manual ..

I'm thinking something happened. I've run through many, many cells (commercial use) on this charger without issue. I'm running the same program on 4 sets of cells since the original post no problems. I've also run the suspect cells though the backup C9000 and no problem. It's this one off situation that irks me... All the batts were hot, not just one or two of the four.

So again... Never charge unattended


___________
Posted from my phone.

This might also be a poor contact issue. I have observed a couple of times when inserting a cell in my C9000 to stay in IRC check forever and increasing gradually the voltage test from 1.45 to 1.65 (after a couple of minutes) where I take the cell out and re-insert it (in the same bay) and everything works ok; happened on a relative new eneloop and another old duracell cell (got these within 2002). This might be a microprocessor glitch or poor contact matter. Your cells might not be firmly inserted at the bay and the thermal detectors are not in the "correct distance" to measure the temperature correctly.

Ualnosaj said:

It's the chargers fault if it's still going when the surface temperature of the batts are measuring 70 deg C. and it's still going, yes? Is 158f not enough to trigger a thermal shutoff?

Using only this page for reference it appears the C9000 has a cutoff of 135f...

http://www.fatwallet.com/forums/deal-discussion/881250/

Two of these are year old AA Eneloops by the way folks. Two are regular Sanyo 2700 AA Nimh.

Click to expand...

OK, that's more information. As others have said, maybe it was a battery contact issue, or a charger glitch. Thermal cutout is unreliable in loose AA chargers, unfortunately. The heat has to be conducted out of the battery and into the sensor. Thermal tests are more of a last resort safety feature than an early termination mechanism.

Perhaps it was a one-off incident, not to be repeated.

Wow, that is quite hot. Most the cells that mine sees are Eneloops and I've not encountered this. I'd likely smell the warmed up wrappers/plastic and this would alert me something isn't happy. What batteries out of curosity and their usage stats...etc?