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Overly sensitive NiMH battery chargers

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IanB:

--- Quote from: Rick Law on July 30, 2019, 06:02:19 pm ---First, As said already, battery with low voltage is damaged battery so you cannot expect it to be "normal."
--- End quote ---

Just because it's been said doesn't mean it's true.

I have a Harmony remote that eats batteries. I will put 4 AAA Eneloops in it, and often by the time I notice the remote has switched off one of the batteries has been drained to zero or even reversed. I never have any trouble recharging a battery in that state and there are no particular signs of damage. Such a drained battery still tests just fine.

Summary: a low voltage battery may not be the fault of the battery, it may be a result of battery abuse. Good batteries can take abuse better than bad batteries, and abused batteries are not necessarily damaged.

Also, none of the chargers I regularly use complain about charging batteries that have been drained to zero. They charge them just fine. (These are Panasonic chargers and the Maha C9000.)

IanB:

--- Quote from: ogden on July 30, 2019, 01:47:53 pm ---
--- 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.

--- End quote ---

If a battery is "hot" during charging rather than "warm" then I consider it battery abuse and will not use that battery/charger combo again. I also will not use a 1C charge rate regardless of datasheets that suggest it is OK. Whatever a manufacturer might claim for whatever reason, common sense also has to be applied.

For similar reasons I don't drive my car fast over holed and rutted roads even though the manufacturer may test it that way. I don't regularly drive my car on racetracks at the limit of its performance. I don't routinely drive my car with the revs close to the red line, even though the rev limiter hasn't cut in.

There is a difference between upper operating limits and good practice.

magic:
NiMH certainly can be discharged to absolute zero and charged back with no problems. They will even self-discharge in a few years, or the crappier ones in a few months.

Cell reversal supposedly harms them, perhaps it's less of a problem at low currents like in a remote :-//
And I think it was NiCd which really, really hated cell reversal and easily got damaged.

And yes, I hate "smart" chargers which aren't smart enough to charge a completely drained battery.

james_s:

--- Quote from: ogden on July 30, 2019, 07:52:16 pm ---
--- Quote from: james_s on July 30, 2019, 07:32:49 pm ---My BC-900 charger fails to recognize batteries that have become overly discharged.

--- End quote ---

Yes, treshold for LaCrosse BC-chargers is 0.5V. If you have such NiMh batteries - either you are using battery set(s) with huge capacity spread, your tool/device/whatever is not designed for rechargeable batteries or your batteries just lost capacity and shall be recycled.

--- End quote ---

It's things not being designed specifically for rechargeable batteries mostly, generally not a problem but sometimes I forget to be proactive and batteries get drained too far, doesn't seem to hurt anything but it's an inconvenience to have to put them in a dumb charger for a bit to resolve that. I also have a few older non-LSD batteries which work fine in some applications, no sense in disposing of something that still works, but if they are not used for a while they self discharge and I have to use the same trick. It's a minor annoyance but it could have easily been solved by a simple firmware change to allow one to override the detection and force it to start a charge cycle.

David Hess:
NiMH end of termination is tricky to detect.  One thing to watch out for is charging too slowly which makes it even more difficult.  I use C/4 now as the slowest charge rate.

I have had a Maha C9000 long enough to wear out a complete set of AA and AAA Eneloop cells.  At one point, my Maha C9000 started having problems like you describe.  I found nothing wrong with the power adapter so I took it apart and suspected that the aluminum electrolytic capacitors had worn out.  I replaced them with some 20+ year old solid tantalums and now it works like it should.

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