zener diodes for cell balancing?

[ghoti]

My search on this forum for "zener diode" showed nothing regarding cell balancing. It seems to me that a zener diode of about 3.3 volts (or some appropriate voltage) in series with a resister to limit current, placed across a Lipo cell will draw it down to that zener voltage and stop draining the cell. Were one of these circuits applied to each cell in the pack then all cells would come down to the same end voltage and then be in a state of balance. Is there anything I am overlooking here? A 3 cell pack would take three resisters and three diodes and that is simple and cheap and foolproof. Is this real? Comments? fish

[Afroman]

Hiya
One of the biggest problems you will find with zeners is that they are quite simply, not accurate. A "3.3V" zener might start clamping at 3.0V, then have a max clamp at 3.6V. Changes in temperature and current will affect the zener voltage a LOT. Also, the consistency between zener diodes is not so great either.
Also, im not really sure I see what is stopping the battery voltage from dropping below the zener clamp voltage here.

[Dan Baldwin]

Another problem is that Lipos need to be balanced at or near a full charge, not at 3.3 volts.

Dan