MH-C9000, Voltage fluctuation during discharge.

SweD

Newly Enlightened
Joined
Oct 14, 2008
Messages
62
Hi all,
the strangest of things is in the middle of being played out before my eyes.

I have an old Energizer NiMH 2000 mAh cell in slot 3 of my C9000, it's been good to me since 2007 or whatnot, the charger that is.

I had a look at it a few minutes ago, Voltage being at 0.96, I thought, ok, that is a crap cell, considering how much energy had been pulled so far.
Now, some half an hour later, and some 200 mAh later, the Voltage is up to 1.02, I did see it being at 1.03 as well.

All of this happening during a discharge cycle, no charging involved, I must say it's a first for me seeing a cell go up in Voltage during discharging, which makes me think that it's not, and that the C9000 has thrown a fit, but it worked fine yesterday, however, for four other cells, so who knows.

Has anyone else observed anything of the sort?

Regards,
/Dennis
 

SilverFox

Flashaholic
Joined
Jan 19, 2003
Messages
12,449
Location
Bellingham WA
Hello Dennis,

I have seen this several times with older cells.

The "theory" is that areas inside the cell become electrolyte starved. During a discharge the electrolyte can adjust slightly finding new electrode material. This results in a slight change in voltage.

At this point I would consider your cell as trash. You can try to recover it by doing a Break In cycle, or several cycles, and see if the cell discharge goes back to normal. Another option is to only use that cell in a single cell light.

Tom
 

SweD

Newly Enlightened
Joined
Oct 14, 2008
Messages
62
I was going to use it in a a single cell light, actually, so we'll see. It's still discharging, 1300 mAh so far, and is still around 0.98V, hovering around the 1.00 mark. Might well be the full 2000 before it decides to drop, who knows. :)

/Dennis
 

apagogeas

Enlightened
Joined
Mar 13, 2011
Messages
210
I think it has to do with the cell getting warmer during the discharge, which results in lowering the internal resistance. This is pronounced on cells with quite elevated internal resistance, so we talk only for older cells anyway. It might also be what Silverfox suggest. I had many such cells - of HSD type - do that.
 
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