A friend of mine has just finished his race car but is having fan issues. What I want to help him do is setup an LED that turns on when the fans have lost power. Often the fuse blows.
I would assume I can tap off the 12V supply that is after the fuse to send to the relay but how would you wire it up..?
Best Answer
If you don't want to bridge the fuse, you can add a relay in series with the fuse. Choose a relay that is closed when no voltage is applied to it (called SPST-NC for Single Pole, Single Throw, Normally Closed) and connect the LED to this relay.
When the fuse blows up, the relay is closed and the LED turns ON. This solution makes sure that your LED circuit is perfectly insulated from the fan circuit.
For example this relay can be used: http://uk.farnell.com/coto-technology/9001-05-02/reed-relay-spst-5vdc-0-5a-through/dp/1079820
Make sure the current and voltage ratings match those of your circuit, though.