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Bad NiMh Cells from eBay??
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Author:  bereshr1 [ Sun Feb 06, 2011 6:03 pm ]
Post subject:  Bad NiMh Cells from eBay??

Hey All.
I recently built an extended battery for my Canon. Used the dummy battery method matched to a 6-AA battery holder. It all goes together really well. Thanks to whomever posted the technique.
However, I wanted to see if anyone here has gotten a "bad batch" of NiMh cells off of eBay? I had picked up a number of Tenergy branded cells, 2300mAh, a while back for another project. Also got the Tenergy "smart charger". The cells only charge for about 15 minutes before the charger's indicator light turns green. They register 7.8v, but when I hook up the battery, the camera indicates that it has low power.

I'm also just realizing that maybe the non-power contacts on the battery that are now non-operational may have something to do with communicating charge condition to the camera.

Any ideas? Thanks much.

Bob

Author:  Antz [ Sun Feb 06, 2011 7:10 pm ]
Post subject:  Re: Bad NiMh Cells from eBay??

If you have 6x AA rechargeable, that's about 1.2volts each, or 7.2 volts total.
7.8volts sounds about right for fully charged, possibly slightly low.

Most the chargers for the canon gear put out 8.2 ~ 8.4 volts to charge the batteries.

Depending on the model of camera, the low voltage cut-out point is probably around 6.8v, so I would expect that by the time you put a bit of a load on your batteries the overall voltage will be dropping pretty close to the cut-out point.

It would pay to check the voltage of each cell individually when they are charged to see if you have one that is lower than the rest. Even better, check the voltage across each individual battery while they all have a load on them to see if there is one lower than the rest. If you have one with high internal resistance it will screw things up.

Author:  bereshr1 [ Sun Feb 06, 2011 10:00 pm ]
Post subject:  Re: Bad NiMh Cells from eBay??

Hey Antz.
Thanks for the suggestions.

Charger Voltage: 11.85v
All cells unloaded "charged": 8.15v
All cells loaded: 8.13v

Individual Cells (loaded):
#1: 1.35v
#2: 1.35v
#3: 1.36v
#4: 1.36v
#5: 1.35v
#6: 1.36v

The unloaded voltages on the cells is the same as the loaded voltage.

Mystery continues. I also power a Little Bramper with the same cells and have a similar suspicion.

Thanks for the feedback!

Bob

Author:  Antz [ Mon Feb 07, 2011 11:18 am ]
Post subject:  Re: Bad NiMh Cells from eBay??

Sounds like the batteries are OK then.
You'll normally see one of them do something significantly different voltage-wise if you have a cell go bad.

Author:  bereshr1 [ Mon Feb 07, 2011 12:08 pm ]
Post subject:  Re: Bad NiMh Cells from eBay??

Bummer. At least it takes the cells out of the equation. I'll look to the charger to see if there's an issue there.
Thanks again for your help. Wouldn't want to get stuck without juice.

Bob

Author:  flyvholm [ Tue Feb 08, 2011 4:38 am ]
Post subject:  Re: Bad NiMh Cells from eBay??

I had the same problem. If I remember correctly several of my cameras behaved irregularly using NiMH battery packs, and in particular I remember my 40D wouldn't switch on at all. I am clueless as to why they won't work, especially since some battery grips take NiMH batteries. Given that Li-Ion battery packs work fine I decided it wasn't worth the headache and ditched NiMH altogether (they die much faster in the cold anyway).

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