Electronics > Beginners
Overly sensitive NiMH battery chargers
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Rick Law:

--- Quote from: 13hm13 on July 30, 2019, 06:05:28 am ---...
...
EDIT:
After a test with the paper-clip trick on the C204, the charge did conclude (green light) ... but both batts. were too hot to touch. This is not normal.

--- End quote ---

May be I should have mention this caution in my last reply also:

When your battery has low voltage and/or gone-negative, they are damaged battery.  You cannot expect it to be normal.  The hope is that it is not too damaged and became useless.

I had recovered 800mAH AAA (gone negative) back to nearly 800mAH, and I had recovered 2000mAH AA back to just 17mAH.  At 17mAH, it is good as dead.  Damaged battery likely have higher internal resistance and will heat up more.  It should be charge as lower current.   As to it is useless or not, it is up to you to decide.

I don't know the options on the Maha MH-C204.  Both my better chargers (LaCross BC700 and Opus BCT3400) have a cycle mode called "discharge-refresh" to improve your battery.  It is what I used for damaged battery recovery.  It charge full and discharge (while measuring the mAH) a number of times.  This "exercising" the battery do help unless your battery is at or near-death.  But if your battery gets hot, run your charger at a lower current likely will help it from getting as hot.   1/10 C is what I use for recovery, but you can try even lower.  (If you don't know C: C is the capacity.  2000mAH battery is C=2000, so 1/10 C is 200mA)

My LaCross BC700 NiMH charger (when selected) will do such cycle indefinitely until the mAH stop getting better (higher).  Sometimes it runs for days cycle after cycle.  In the end, the battery does come out working much better.  My Opus BCT3400 NiMH+LiIon will do such cycle but limited to 3 cycles.  That 800mAH battery that I recovered was at 400mAH range at the first cycle.  By the time it was done, it was 790mAH range (798 if I recalled correctly).

If your Maha MH-C204 have such options (charge full then discharge with mAH measurement), try it a few cycles and see if it helps your battery recover some.  If your battery is not too damaged, it probably would recover a bit - but never back to as good as before damage.

Don't forget - If you want it to run cooler, try it with lower current setting.
13hm13:
As i noted in the OP, in the old Lenmar charger, I can successfully re-charge the batts. that faulted in the Maha chargers. Using those charged batts in devices yields fairly normal results (maybe a bit on the low side).
I question the quality and design of Maha products.
ogden:

--- Quote from: 13hm13 on July 30, 2019, 11:48:54 am ---As i noted in the OP, in the old Lenmar charger, I can successfully re-charge the batts. that faulted in the Maha chargers. Using those charged batts in devices yields fairly normal results (maybe a bit on the low side).
I question the quality and design of Maha products.

--- End quote ---

Fact that dumb charger is able to charge battery do not mean that both Maha chargers are faulty :)

As you do not tell measured capacity just  "fairly normal results" which could be as low as 100mAh. For 2A pulse Maha Powerex charger my estimate is that you need at least 0.5AH battery for charger to not refuse it with "too high voltage" (meaning high impedance) claim. Before continuing to blame Maha (Powerex) charger, you really shall cycle/test batteries and measure their real capacity. When Maha charger refuses to accept battery - take your time and measure it's voltage using multimeter.
IanB:

--- Quote from: ogden on July 30, 2019, 07:03:40 am ---
--- Quote from: 13hm13 on July 30, 2019, 06:05:28 am ---After a test with the paper-clip trick on the C204, the charge did conclude (green light) ... but both batts. were too hot to touch. This is not normal.

--- End quote ---

Hot NiMh's in the end of fast charge is completely normal.
--- End quote ---

Batteries too hot to touch at the end or charging is not normal. It is a sign of bad batteries or bad charger. If you have a "fast" charger that regularly does this it should not be used.

At the end of charging batteries should be mildly warm at best, certainly not hot.

For safe, moderate charging of Eneloops I recommend you to check out Panasonic chargers, for example the BQ-CC17. Or if you have a C9000 use that, but keep the charge rate at 1000 mA for AA batteries (use 400 mA for AAA).
ogden:

--- Quote from: IanB on July 30, 2019, 01:45:22 pm ---
--- Quote from: ogden on July 30, 2019, 07:03:40 am ---Hot NiMh's in the end of fast charge is completely normal.
--- End quote ---

Batteries too hot to touch at the end or charging is not normal.

--- End quote ---

Please define "too hot to touch" in degrees (Celsius).

[edit] Panasonic pro NiMh recommended charger specs attached. Note that rapid charge ambient specified is 0..40oC. As 2Ah AA self-heating at 1C charge is +10 degrees and delta T termination needs couple of minutes of ~2oC/minute raise, some who charge his batteries in hot place could get quite a hot batteries in the end. Also note that AA have max 55oC allowed which as far as I know shall be considered as "too hot to touch". As you see - it depends.
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