Need signal when engine is on to drive a relay

[LagunaH1]

Hi everyone,

I'm considering inserting a relay in to my aux battery circuit such that I have a "fool proof" disconnection when the alternator isn't running.

I've never done this before so: Where might I find a 12 volt signal which is ON when the engine is running? I'd want to use that to drive a relay.

[Cactus Red]

On an '09, the Cig Lighter plug is on when the key is on. The AUX power plug is on all the time.

[nts007]

I believe he is thinking not a switched key on circuit but an actual running engine wire. I don't believe there is anything you can tie into. But you could run a wire off the back of alt to a voltage sensitive relay. One that closes when 14.2-14.4v is generated. With alt not running voltage is usually 12.5-12.8 on that wire. So a voltage tripped relay? I've never looked for one before but they must exist

[LagunaH1]

Thanks for the suggestions guys. Yes, I'm pondering a way to trip a relay only when the alternator is turning and generating current.

Edit: I might just go for one of the ignition switched cig power outputs, seems so much easier and almost as good.

[Reloaderguy]

Magnetic Latching Charging Relay.

https://www.bluesea.com/products/7622/M ... 2V_DC_500A

EDIT: I'm not sure I understand what you're asking. If you mean a relay to power accessories that trips only when the alternator is charging I'm not sure how to accomplish that...maybe with diodes? The battery will backfeed the relay. If you just mean to charge the aux battery then the MLACR is the most logical.

[nts007]

Voltage sensing isolator
http://www.marinco.com/en/710-140a
Engages at 13.2 volts
Disengages at 12.7

You can literally run it between main batt and secondary or straight off alt output if you want. Same connection

Found one here for $93. Same one I think
http://www.westmarine.com/buy/marinco-- ... --14152185

[Reloaderguy]

Voltage sensing isolator
http://www.marinco.com/en/710-140a
Engages at 13.2 volts
Disengages at 12.7

You can literally run it between main batt and secondary or straight off alt output if you want. Same connection

Found one here for $93. Same one I think
http://www.westmarine.com/buy/marinco-- ... --14152185

That is only 140A. If you bridge the two batteries to power the winch you'll have problems. My OE alternator puts out 200A alone. The MLACR I linked to is rated to 500A and can bridge multiple banks of batteries.