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MiMH questions

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3v0

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I have Googled without much luck.

I have been buying EverReady MN15-AA 1850mAh cells. I am using an EverReady Energizer CH30MN which I think is a 30 minute charger. It monitors each cell separately.

After a while the charger refuses to charge some cells. Is there some way to reclaim these cells?

How much longer would the cells last if I used a slower charger? If so (I should duck here) a link to a slower/better charger circuit would be helpful.

Does using cells in low draw devices like remotes and mice cause the cells to go bad?
 
NiMH cells self-discharge too quickly to be used in something like a remote. Personally, I do not consider a mouse to be a low load. Such low loads do cause deteroriation (not necessarily damage) to lead-acid cells. Not sure about NiMH because no one uses them for that due to their self-discharge.

Don't know about the charging thing though. Try a better charger? NiMh dies out after 200-300 charges. If you fast charge them I think it cuts their life by 1/4 to 1/3. You probably wouldn't notice it.

Voltmeter a cell, see if it's polarity is reversed and see if it's below 10V (both are bad, duh).
 
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I would guess these have been charge/discharged maybe 20-30 times tops.

3 AA cells that cause the charger to blink red, its failure mode.

Voltages are all +
a) 1.3
b) 1.2
c) 1.0

Cells a and b are marked 2300 mAh.
Cell c is marked 1850 mAh

These cells are supposed to be 1.2V cells so the reading are curious.

Put cells a and b into my DMM and it said "low bat".
 
1.2V is just the nominal voltage. It falls and rises with capacity. Anything below 1V is not good for NiMH cells. Are your voltages fully charged or empty? Have you tried a good battery in your DMM?
 
According to
**broken link removed**

  • When charging the battery for the first time the device may indicate that charging is complete after just 10 or 15 minutes. This is a normal phenomenon with rechargeable batteries. Remove the battery from the device, reinsert it and repeat the charging procedure. When charging the battery for the first time the device may indicate that charging is complete after just 10 or 15 minutes. This is a normal phenomenon with rechargeable batteries. Remove the battery from the device, reinsert it and repeat the charging procedure.
  • It is important to condition (fully discharge and then fully charge) the battery every two to three weeks. Failure to do so may significantly shorten the battery's life (this does not apply to Li-Ion batteries, which do not require conditioning). To discharge, simply run the device under the battery's power until it shuts down or until you get a low battery warning. Then recharge the battery as instructed in the user's manual.
It does not specificaly say that this is in regard to any one battery technology.

I doubt many people bother with the conditioning. I pulled two good cells from use and will attempt to charge and fully discharge them several times to see if it improves their ability to takea charge.
 
i have a pair of MiMh's for my laser, and even after about 100 charges, the laser is still as bright as it was when i first got the bateries, i didn't know you had to completely discharge them???????
 
things said:
i have a pair of MiMh's for my laser, and even after about 100 charges, the laser is still as bright as it was when i first got the bateries, i didn't know you had to completely discharge them???????

You don't for NiMH. Are you actually talking about MiMH (whatever that stands for, or is it a bunch of people just making the same typo?)
 
dknguyen said:
1.2V is just the nominal voltage. It falls and rises with capacity. Anything below 1V is not good for NiMH cells. Are your voltages fully charged or empty? Have you tried a good battery in your DMM?
The DMM works fine with a good battery. It was never in question.

These are the cells that the charger refused to charge. It blinks when you try to charge them which indicates a bad cell. I would guess that they are empty, but since the charger will not deal with them I only have the voltage reading to go by.

If these cell were near the end of their expected life I would not bother. They are too young to die.

Since I last posted I placed 4 AA in a pack with the idea that I wanted to drain them down further. 3 were the questionable ones from the earlier post. The 4th was a good cell. The pack was hooked to 13 LEDs with internal resistors, current was 75 mA. The voltage under load was about 3.5V. After an hour or two I took the cells and placed them in the charger. One of the unchargable cells is now charging. It is cell (C) which had 1.0V to start with.

It will be interesting to see if it goes to a near full charge.

EDIT: Cell (B) was then placed in pack with 3 charged working cells including cell (C) and allowed to run the 13 LEDs for about 2 hours. It will now take a charge.

Cell (A) has been run for 4 hours with 3 charged working cells but does not take a charge. Its voltage has been reduced by .1V to 1.2.
 
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