Circuit Needed for Alarm Light

[macbeth]

I'd like to add an alarm light to my control panel so that if the alternator stops charging (e.g. if the fan belt belt breaks), the light will come on.

I've seen the circuit before somewhere, but can't remember it. I think, you have to apply +12v from the battery to one side of the light, and the positive output from the alternator to the other side, so they cancel out when everything is fine, but the light goes on when the 12v is not coming from the alternator, or something like that.

Can any electrical wizard help me out please ?

[hellosailor]

You'd need to start with a circuit diagram of your electrical system since they are "all" different. If your alternator was a conventional "3 wire" like a car, there's already a circuit that lights a light when the alternator fails. If you don't have that...you've got to find out what you have to consider options.

[macbeth]

Originally Posted by hellosailor

You'd need to start with a circuit diagram of your electrical system since they are "all" different. If your alternator was a conventional "3 wire" like a car, there's already a circuit that lights a light when the alternator fails. If you don't have that...you've got to find out what you have to consider options.

Now let me try and remember ! The alternator, which can output 80amps, has a big fat output terminal. It has a field line, which is green in colour. It has an earth line, I think it might have a line to the rev counter.

Hmm ! I'll have to check when I go down to the boat tomorrow or Wednesday !

Thanks, that a start.