I'm not sure if Ni-cd will have problem for long storage and seem not see
such warning before, I only know sealed lead acid or normal lead acid cell
cannot be left in discharge mode. For safety, Ni-cd supplier will delivery
cells at discharge mode. I fond the crystals around the cell happen to the
cells I used periodically or left unused for long period. Actually I charge
the cells after use but it didn't prevent the problem happen.
C.H.Ling
----- Original Message -----
From: <HI100@xxxxxxx>
>
> CH is correct about this as far as the discharge is concerned but there is
> another failure mode if the cells are left fully discharged, for extended
> periods. This applies particularly to old cells. NiCd's are sealed with
an
> elastomer. Under charge the cells generate pressure internally that tends
to
> apply more pressure to the seals increasing their effectriveness. The same
> pressure also tends to compress the seals over many charge discharge
cycles.
> Eventually if left fully discharge the electrolyte gets through the seals
> and the cells slowly dry out losing capacity. If you examine old cells you
> can often find crystals around the top at the seals showing evidence of
> leakage. So old cells last better if left on a very low float charge or if
> you recharge them every few months if unused. Most chargers do not have a
> very low float float current at charge end. You can make your own float
> charger with a resistor and diode and a low voltage wall wart power supply
or
> equivalent. Just select the resistor to give a current of say C/100 or
C/200
> where C is the battery capacity. So for example for a 1Ah battery
(1000mAh)
> choose a current of 10 or 5mA . Put the diode in series with the resistor
to
> stop the cells discharging if power goes off.
>
> Regards,
> Tim Hughes
> >>Hi100@xxxxxxx<<
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