Re: How are consumers affected by NiMH and Li-ion cell voltage reversal?
- From: Chris Carlen <crcarleRemoveThis@xxxxxxxxxxxxxxx>
- Date: Thu, 06 Apr 2006 08:23:16 -0700
Michael wrote:
Chris Carlen wrote:
It seems cells need to have a diode built in to limit reverse voltage to
a non-damaging or at least a very minimally damaging level (maybe a
Shottky).
What? And drop the screwy 1.2v to an even lower value?
No, the diode goes antiparallel to the battery -- reverse biased by the normal cell voltage, but pointing in parallel to the normal direction of current flow through the battery. The diode is not in series with the cell, so does not drop voltage when the cell is providing voltage. The the diode does nothing until the cell voltage collapses. The diode then turns on to conduct the current being generated by the remaining cells which still have capacity. The diode forbids the reverse voltage across the dead cell from exceeding the diode drop, which in the case of a Shottky, would be about 0.4V.
Perhaps -0.4V across a cell is still damaging, I'm not sure. Would need an electrochemist to comment on this. The diode would also not interfere with charging in any way in this arrangement.
--
Good day!
________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@xxxxxxxxxxxxxxx
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