On Wed, 1 Jun 2005, Wouter van Ooijen wrote:

> A customer let the smoke out of a H-bride motor driver I made for him,
> so now I want to add reverse-power protection. My standard anti-parallel
> 1N4004 won't do much good when connected to a lead accu, so I am
> considering a series diode (1N4004, or a schottky). But now the back-emf
> from the motor, which is fed to the power rail by the 4 diodes, has
> nowhere to go. What is the solution to this? A big zener on the power
> rail, for let's say 150% of the maximum power supply? If so, which
> wattage would be needed? Or maybe a consensator? If you, what capcity
> and what type? Or are there other solutions, maybe with a polyfuse?

How much power is in that line and can you afford a breaker ? A simple 
circuit using a crowbar mosfet or thyristor can activate the breaker. Or 
pop it if it has a popping coil. There should be something there because 
lead acid batteries + plastic insulated wiring = fire hazard.

Peter
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