Re: reverse biased Ni-Cad cells

From: w_tom (w_tom1_at_hotmail.com)
Date: 12/21/04 

Date: Mon, 20 Dec 2004 23:24:33 -0500

  A voltage reversed NiCd is typically due to a weaker cell
being in a stack of other stronger cells when the entire
battery pack is too discharged. Sometimes a negative cell
could be corrected by hitting the cell with higher current in
the reverse direction. On older cells, this would
(theoretically) burn out the reverse section. Then that cell
would be recharged. This technique has not been very
successful for me with newer technology NiCds. But then you
would only be restoring that reversed cell so that operation
can continue until a new battery pack is obtained.

  Again, the most probably reason for such a destructive
failure - battery pack was permitted to discharge well beyond
what should have been its lowest limit causing its weakest
cell to become reverse charged.

aurgathor wrote:
> A quick check on a 6 pack containing D size Ni-Cad
> revealed one with -0.4V, another with -0.1V. I know
> that's not a very good thing, so here are my questions:
>
> a) is there some simple circuit that could be used
> to prevent this? I'm thinking of a parallel Schottky
> diodes, but preferebly with a Vf under 0.1V.
> How low can Schottkies go, BTW?
> b) how much damage can reverse voltage cause,
> and how quickly?
> c) what should be terminal voltage when discharing
> Ni-Cads? I plan to build a discharger from a battery
> holder where they would discharge through some
> series diodes and a resistor.
>
> TIA

Relevant Pages

  • Re: reverse biased Ni-Cad cells
    ... A voltage reversed NiCd is typically due to a weaker cell ... burn out the reverse section. ... can continue until a new battery pack is obtained. ... failure - battery pack was permitted to discharge well beyond ...
    (sci.electronics.components)
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  • Re: My NiMH cells reversed polarity! Oh no!
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    (sci.electronics.design)
  • Re: My NiMH cells reversed polarity! Oh no!
    ... No need for cell *failure* to ocurr for the polarity to go reverse during ... the discharge of a battery. ... impedance goes very high so it can easily take up a small reverse voltage. ... The reverse voltage cells will recover normal polarity when charged as usual ...
    (sci.electronics.design)
  • Re: reverse biased Ni-Cad cells
    ... > A voltage reversed NiCd is typically due to a weaker cell ... > battery pack is too discharged. ... > burn out the reverse section. ...
    (sci.electronics.design)