Electronics > Beginners

Overly sensitive NiMH battery chargers

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Rick Law:
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By the way, this is important and I kept forgetting to put it in
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The trick is for NiMH only!  Do NOT attempt the paper clip trick with LiIon battery.  Doing that could give you a very very unpleasant afternoon - not just that day but there after.

Shorting a good LiIon with a bad/damage LiIon can easily cause major problems!
******

Now back to the conversation:


--- Quote from: ogden on July 30, 2019, 01:04:06 pm ---
--- 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.

--- End quote ---


First, As said already, battery with low voltage is damaged battery so you cannot expect it to be "normal."


--- Quote from: IanB on July 30, 2019, 01:45:22 pm ---
--- 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).

--- End quote ---

Second, I am not sure it s fair to blame the Maha charger on it getting hot.  Recall one has to trick the Maha to charge a rejected battery that it doesn't think it should charge - so, one cannot trick it to start then blame it for not doing it right.

No doubt Maha could have designed a much better charger.  In practice, they really can't do that without making it exceedingly complex and/or expensive.  Imagine having to look up the battery spec to set "termination voltage", "termination temperature", etc. etc.  So they have to make trade off decisions.  If the Maha is meeting it's own specs, that all we can ask for.

(13mh13, below is mostly for you)  Since you did the tricking of the Maha to start so you can try to "rescue" a damaged battery, you should expect things wont be normal and extra precaution has to be taken.  I don't do as much safety measure with NiMH as I do with LiIon, but if/when it reached "too hot to HOLD" (which would be cooler than "too hot to TOUCH"), I would be very cautious.  Likelihood is, if it is that hot, the battery is probably too close to death to be worth using.

Take note on the end-charge temperature, take note on other clues.  Remember you ARE the Emergency Room trying to "bring it back from the dead".  You "got the heart beating" by using a paper clip.  Now don't send the patient out the door right the way to drive home by himself as if all is well and normal.

I don't think you necessarily need a lot of tools.  You do need the a way to measure charge temperature, charge voltage, the charge time, and the actual "fully recharged" capacity.  Those will be like the blood pressure, heart rate, and temperature of your patient in the ER.  The ER wont let you leave without looking carefully at your "pre-exit" vital signs.  You shouldn't put your battery into circulation (treat as normal) until you scrutinize the battery's vital's.

ogden:

--- Quote from: Rick Law on July 30, 2019, 06:02:19 pm ---You shouldn't put your battery into circulation (treat as normal) until you scrutinize the battery's vital's.

--- End quote ---

When you have many (more than 4) NiMh's, you want to know actual capacity of each battery so you can "balance" pairs/4-packs of them by capacity to minimize polarity reversal of weakest in the pack. This conversation is quite long already, yet we still don't even know actual problem - charger is refusing batteries due to low voltage or lost capacity. I don't want to hurt anybody's feelings, but to me this thread looks like smearing of Maha Powerex charger&batteries to promote Lenmar charger&batteries.

[edit] Answer to original question is: No, you can't change anything about Maha's charger because it is microcontroller-based and for sure it's firmware is read-protected.
[edit1] If Maha do not work for you, then get Lacrosse BC1000

james_s:
My BC-900 charger fails to recognize batteries that have become overly discharged. My solution has been to keep a regular dumb charger around for times I encounter this issue. I pop them in that for a few minutes and then move them to the LaCrosse charger and it then works fine. It's annoying and I wish the BC-900 had an override button to deal with this but it hasn't been too big of an issue overall.

ogden:

--- 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.

dnwheeler:
I have a set of 4 Energizer NiMH batteries that my Eneloop charger won't charge. This has been true since the batteries were new and doesn't matter if the batteries are charged or discharged - the Eneloop charger always reports an error. The original Energizer charger (came with the batteries) and an intelligent universal (NiMH + Li-Ion) charger both work fine.

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