Alternator Field Disconnect or not?

[ronrobbie7]

I have an 89 Mercruiser 5.0. I am adding a second battery and would like to add a guest or perko selector switch. How do I know if I need the switch with or without AFD? Thanks for any help

 

[bruceb58]

Re: Alternator Field Disconnect or not?

You don't have to have one as long as you make sure you never turn the switch to off while the engine is running and to get a switch that has a "make before break" contact. Basically, what that does is that when you switch from one battery to the other it basses through the "both" position and there is never a time where at least one battery is not connected to the common terminal of the switch.

 

[ronrobbie7]

Re: Alternator Field Disconnect or not?

Thanks for the help. I wasn't sure if it had to do with internal or external regulator or not. Thanks again.

 

[Boatist]

Re: Alternator Field Disconnect or not?

If you have an external regulator then I would get the one with the field disconnect circuit. They do no cost that much more and sure cheaper than a new alternator if someone turn thru off with the motor running.

If you have an internal regulator then really no way to hook it up to kill the field winding and save the alternator with out making internal changes to the alternator.

As BruceB58 said Get a Make Before Break type switch and never turn thru off with the motor running.