Relay or Mosfet as switch.

Other Hardware General Electronics
1

Hi,

Im not too sure what I'll need.

Ive added a second battery and alternator to my car. I want a relay to be turned on by the ignition, to switch on the charge/excite circuit of the alternator.

At the moment the excite circuit is coming straight off the ignition, with a charge light. But this is causing engine interference (a whistle) that disappears, if alternator number two is excited by battery number two directly. Thus the desire to have a switch/relay.

If you're not familiar with how alternators works. They need 12 volts to excite the electromagnet that produces power from the motion of the engine turning it.

Thank you

2

Why not just get a diode isolator and let one alternator charge both batteries?

3

Ive got everything fitted and wired up almost perfect. Im thinking of trying the kind of relay that are used for heat lights and putting the + through it.