DIYbanter - View Single Post - Seriesed battery cells irregular charging

N_Cook

On 26/09/2017 23:45, wrote:
On Tuesday, 26 September 2017 19:22:21 UTC+1, N_Cook wrote:

Silly wind-up torch but could be anything using Ni-Cad or ni-Mh
multi-cells. LEDs are full bright for a short time after winding up ,
then drops to low light level, regardless of amount of winding beforehand.
One cell is out of kilter with the rest, and in use discharges quickly
compared to the others.
Bench ps charging that one , in isolation, cures the problem.
But presumably it may return , unbalanced charge/discharge across the
cells.

likely discharge in the cell from a dendrite. If so the cell's at end of life.

How to do the isolated charging of one cell properly, the next
time in the way of monitoring voltages and charge currents ?

The easiest way is just overcharge them, but it must be done at slow charge, ie 16hr charge rate.

The practical answer is new cells. They're very cheap.

NT

Not a dendrite problem,not dropped to zero, just gone out of kilter.
16 hour charge time for 30 hours or so , for all 3 in series, makes
sense, the next time.
3x 20mAh (not 200mAh) Ni-MH cells, very small , for a tiny pocket size
version.
Other than 9V pp3 and robbing 3 cells, I'm not aware they are sensibly
(ie not 1000 minimum) available, even then pp3 ones are about 10 times
too big.
I was thinking of a 5V supercap might work as a replacement, if necessary