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Old Aug 26, 2007, 10:13 PM   #1
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My heretofore SONY CycleEnergy NiMh Battery Charger (BCG-34HC) charger is like 18 months old, and have used it perhaps 10 time to charge my digital camera's (4) NiMh batteries. Has always done so, and always done it in like 1 or 2 hours.

Yesterday I tried charging another 4 NiMh batteries -but this time the SONY CYCLENERGY Charger - instead of automatically cutting off when the batteries were all charged - it just kept charging for another couple hours, and the batteries when I discovered the problem, were too hot to handle! The charger has that familiar "burnt resistors" smell.

Is this a common problem?

Fred, NY
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Old Aug 28, 2007, 2:37 PM   #2
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Sounds like, for whatever reason, the charger missed the cutoff. The cells may be damaged, you'll know by the charge they now hold. If they're not holding a good charge after this event, I'd replace the cells and charger as well.
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Old Sep 1, 2007, 7:40 PM   #3
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Usually a fast or super fastNiMH charger works by monitoring the voltage of the batteries being charged. Once a NiMH battery reaches a certain level of charge,itwill actually decrease in voltage a little,, just a tiny bit,, but many of the fast chargers are made to sense this critical decrease in voltage and will automatically know that this is the cut off point and will either switch off or go into a trickle mode, so as not to overcharge the cell. Further charging after this point will only heat the battery up.

Sometimes an aged cellwill not charge up like it once did when it was newer. Instead it may NOT decrease in voltage as much as itused towhen it reaches full charge and although it might still decrease in voltage a little, it might be a smaller amount than it did a few months before and the charger may not recognize this drop asa full charge drop. Instead it may see it as just one of the voltage variations it normally sees while the cell is charging up. This will let the charger go on charging as per normal, often resulting in massive overheating and distruction within the cell. It doesn't mean the battery will be destroyed completely, but everytime it happens, you erode the batteries capability to charge up properly. Eventually the battery willbegin to exhibita noticably shorter life and even though youthink you have a well charged up battery, you cannot guess the exact time a cell needs to reach it optimum full state of charge. Heat is the biggest enemy and causes all sorts of chemical reactions within the cell, either burning away needed elements or cooking them to the point that they are no longer able to take part in the batteries normal operation... At this point the trash is the only place fit for the battery...

ALL NiMH batteries will eventually die this way, regardless of whetherthey have been charged up properly or not. It is just a matter of reducing this eventual degradation for a long as possible by charging it asefficiently as possible.

Your batteries may or may not be at fault but you should try other cells in the charger and watch them for signs of charging/overcharging before you condemn the charger. If all NiMH cells appear to overcharge and heat upthen accept your losses and get another charger,, but if some cells charge up normally, it is the cell(s) which is/are faulty. Not every cell is created equally. Sometimes even quality stuff,, fails...!!!

I personally HATE chargers which charge up in less than about 5 - 6 hours because I think they are more prone to problems within the charge laws. I sometime can't wait the 12-16 hours for the best charge cycle so I might get a faster charger but the fastest I have is a 5 hours charger for 4 cells around 2500ma. Other than that I simply use the overnight chargers, knowing this really is the best way to charge, simply because of the better temperature control aspects of the charge up...
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