Light circuit for a pump...

[i1n]

Hi, I need to install a light on our rural fire service (bushfire) pump trailer that will only be able to be turned on when the motor is running. So as it won't drain the battery if left on.

Could anyone offer a solution?

One thought was to use a voltage switch connected to the battery and when the voltage dropped below 12v (or whatever) it would open the circuit. If there is such a thing.

Any help would be appreciated, it's been a while since electronic studies...

Cheers,
Ian

 

[duffy]

I think the voltage comparator circuit will only kick in when the voltage regulator turns on the alternator and charges the battery. When the voltage got above a certain level, it drops out, and I think your lights would, too.

Seems like the way to do this would be to put something on the ignition coil primary that detects AC. Couple of diodes, a cap, an opamp circuit and a driver.

I take it you don't have an ignition switch, or can't rely on it?

 

[crutschow]

I think the voltage comparator circuit will only kick in when the voltage regulator turns on the alternator and charges the battery. When the voltage got above a certain level, it drops out, and I think your lights would, too.

You want the comparator to turn on the light when the voltage is above a minimum voltage (say 13.5V) and off when it's below. I've used that technique to prevent a plug-in car seat warmer from accidentally draining the battery if I forget to turn it off.

 

[i1n]

Many thanks for the replies...

Right well, might head down the comparator road first off...

Cheers!!