Friday, July 23, 2010

Overcomplicated Battery Protector Take 2.



My second take on the battery protector.
The way it works now is: I added a simple monostable relay. The protection circuit itself is powered through that relay. Basically when connected to the battery, nothing happens. There's a push button switch between Battery + and the relay coil end designated to be the positive. When the button is pushed the relay switches on momentarily, the circuit becomes active and if the voltage is above threshold the FET continues to hold the relay on when the button is released. If not then there's nothing to keep the relay on so it just switches off.
Since the FET is only driving the relay coil there's no heat dissipated there.
Also no chance of oscillation: When the voltage dips below threshold the relay cuts out and that's that.
Possible unnecessary and overkill, but whatever. It works.
According to my cheapo DMM It consumes 50milliamps when holding the relay on, which translates to about a 0.6W average. I can live with that.

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