The Murphy Builders Site

I’m in the process of mounting my primary electrical systems on the firewall and am a bit confused about the alternator connections to the contactors. I have a B&C alternator and 20 amp standby alternator. I’m using ANL fuses mounted on the firewall. Do I connect the alternators through the fuses to the output side of the battery contactor or the input side of the starter contactor? Why? Does it make any difference? And, are the ANL fuses bi-directional, i.e. does it make any difference which way I hook them up?
Thanks,
Jerry Folkerts

ANL's are just slow acting fuses and they are indeed bidirectional.

Assuming your B&C alternator has an external regulator then you can switch it off with a separate control switch. The classic architecture then is to connect it to the load bus side (not battery side) of the battery contactor. That gives you the option of running with the battery disconnected as per some certified designs but also lets you kill the alternator with the separate control switch. It also stops any minor discharge between flights.

I'm not saying it is a great idea to fly with the battery off but it is a desired capability for some installations and has been done.

I'd suggest Bob Knuckoll's aeroelectric book and website for best examples of architecture and integration of the second standby alternator.

Ken

Thanks. I have Bob's book, as well as Marc Ausman's new one. Both have schematics that show the alternator going to the starter contactor and the battery contactor, therefor the question. I got a note from Marc today that said it doesn't make any difference whether I connect to the battery contactor output side or the input side of the starter contactor. And indeed, the ANL fuses are bi-directional. Just a piece of metal.
Best,
Jerry