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Old Jul 13, 2008, 5:00 AM   #11
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SilverFoxCPF wrote:
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Hello Itsme,

As far as I have been able to measure, the 15 minute chargers reject cells when their internal resistance gets to around 0.1 ohms.

Tom
Is the cycle count you listed earlier based on when the charger will reject it?
Does a 15 minute charger cause cells to reach a high impedance sooner than using a slow charge?

Silverfox, did you get my PM?

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Old Jul 13, 2008, 8:11 AM   #12
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I don't know the answer to your question,however my energizer rejected so many batteries (some brand new) that I purchased another charger and used it to see if these batteries were really defective or if the energizer was being too selective. I found that I could still use all the batteries the energizer refused to charge. Now,unless I'm in a real bind for time, I use the slower charger with the presumption thatmy batteries will last longer.
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Old Jul 13, 2008, 12:39 PM   #13
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Hello Itsme,

The life cycle count involved a drop in cell performance. Some of the cells tested developed high enough internal resistance to be rejected by the 15 minute chargers, others lost capacity, and some were still going strong, but at reduced capacity, after the 150 cycles.

Yes I got your PM. I will try to make it over there, but things are very hectic right now.

Tom
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Old Jul 13, 2008, 1:26 PM   #14
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Hello Wsandman,

The battery manufacturers recommend charging NiMh cells in 1 - 2 hours. It seems that at slower charge rates, the end of charge signal used by many chargers is not reliable over the life of the cell. If you regularly use a 4 hour charge, and if your charger uses -dV termination, the chances are very good that you will end up ruining your cells through overcharging because of a missed termination signal. Your cells may not get hot, but they will be damaged all the same. If your charger uses a different method of termination, you can then charge at lower rates, but your cell performance may not be optimum when the cell is charged at a lower rate. Cameras tend to gulp large amounts from the battery. Slow charging NiMh cells is better suited to applications that continually sip.

I have found that when the 15 minute chargers identify a crap cell, it is usually near the end of its useful life, or in need of reconditioning. If you have a bunch of cells that the 15 minute charger rejected, you may want to consider running some tests on them to check their health.

On the other hand... If your application is not critical, playing with crap cells can be educational. You can expect some frustration when they don't perform well, but if you have the patience you will find there still is some life left in them.

Tom
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Old Jul 14, 2008, 2:55 AM   #15
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I monitored charging voltage on my Sanyo eneloop charger which is a smart-charger that charges at 0.3A and takes around 7 hours for 2Ah cells. I believe it terminates using peak detection/0dV.

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