LAst evening I put two eneloops in my MH-C9000 to charge up for a Gold Prospecting trip .
About 4 hours or so latter I got up as it was unusually warm , so I removed some bedding , and decided to turn of the powerex .
When I checked the charger it was still running , and had charged some 3500mAh , the eneloops were hot , real hot .
Anyhow I pulled the cells and turned of the charger , but now I have concerns , the cells were really hot , and I was tempted to throw them in water [ but they were cooling of so I didnt ]
I thought the powerex had temp monitoring ? Now Im concerned the Powerex is not nearly as safe as touted .
Charging Nimh's is not very efficient, to charge them to 100% the charger has to put 140% into the batterie. The 40% is energy-loss, that is what heats up the battery. To prevent the batteries from overheating it is recommended not to set the maximum charging current.
The highest temperature will be reached just before the charger cuts out on the maximum voltage (about 1,4V).
Lithium-ion batteries have a much higher efficciency, if they heat up during charging, something is seriously wrong... But with Nimh's, it is normal that they warm up during charging. If they are too hot to touch, then the charging current is too high, or the charger dous not cut out if the maximum voltage is reached.
Its not the "voltage level". When Nimh finish charging, their voltage dips, which is how fast chargers should terminate. Charging at intermediate currents considerably lessens the dip, which means that chargers will miss it. The other option for charging Nimh is at a slow current at a set time.
The MH-C9000 uses a combination of Negative Delta V, Zero Delta V, Peak Voltage, time and temperature to determine the end-of-charge. In addition, proprietary algorithms are used
Newer models of the C9000 will also use 1.47 as a cutoff voltage, assuming it does not terminate earlier from Delta V. It is recommended to charge NiMh at a minimum of .5C, and anything up to 1C is normal and recommended by Powerex. Newer healthy cells will terminate reliably on the C9000 with lower C-rates, but the older a cell gets the more it likes a higher charge rate to terminate reliably with DeltaV. I've only had one AA cell fail to terminate on my C9000, and it was well used and quite old. With that one exception, every cell I have monitored on my C9000 has had the main charge stop at 1.47v and then the charger goes into a trickle charge mode for two hours, after which it terminates.
So this is the first time it's overheated? Maha has 3-year warranty. But even if it's past warranty, maybe you can send them an e-mail to see if they know what's wrong and how much to get it fixed.
It seems like some people get C9000's with a bad bay sometimes. If it isn't just a one-time deal, hopefully they will replace it for you. It's lousy to pay extra for something good and then it fails like that. I've never had mine miss termination like that which makes me think you got a bad one.
"Voltage was 1.4v - when I left to go prospecting"
There's just so much wrong with that sentence!
Electricity and prospecting just seem to be from diffrent centuries, I imagine it's diffrent if you're from a country that didn't use up all it's natural resources eons ago. To me prospecting is something they do in cowboy movies :P
So youve had no issues after that incident, was it the only time it almost blew up your batteries :)?
How about those Eneloops, how well they function?