Main alt wire

I am working on the wiring for my 9a alternator, and per the instructions it shows routing the B+ wire from the alt to inside the plane and hooked to the breaker at the panel. I have the thought that I would like to avoid a wire inside the plane that is not cicuit protected, esp one this size. I realize that the field wire will be on a breaker, but I'm uneasy with that big wire in the cockpit. Has anyone wired the alt more like a car and routed the alt feed right to the batt (or contactor)and used a fuse or fuse link on the circuit.

I use an automotive Maxi fuse mounted between the alternator B nut and the main #2 wire mounted to the starter. I do not use a starter solinoid so the is large wire is hot when the master switch is on. I have used this design on three or four airplanes with no problems to date. If the fuse were to pop there would be no way to reset it in flight. However if this fuse were to blow it is quite possible that the problem would trip the main breaker again if it were reset. In a VFR only airplane my low voltage alarms would alert me to the issue and allow operation under battery power until I could land. In my current IFR capable plane I have a back up alternator should the main fuse or alternator fail.

I am running the alternator output through an ANL current limiter (a fuse) and then through a current shut. These are both mounted on the engine side of the firewall. The wire to the cockpit is picked up at the starter relay on the input side, which also connects to the battery relay. These connections are made with a doubled copper bus bar. From the starter relay, I run 4 AWG into the cockpit for distribution. It is pretty standard Bob Nuckoll's stuff.

Tom Martin said:

I use an automotive Maxi fuse mounted between the alternator B nut and the main #2 wire mounted to the starter. I do not use a starter solinoid so the is large wire is hot when the master switch is on...

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I did that on my -6 and it works fine. Just remember that using the solenoid as the starter contactor (like a car does) requires either a small cube relay to send power to the solenoid or a fairly stout start switch. The solenoid allegedly draws about 20 amps, but I haven't measured it.

Heinrich Gerhardt
RV-6, flying

I redid some of the wiring in my airplane this winter. When I did this I took the B lead from the alt and ran it to a current limiter mounted on the firewall. I have a pullable breaker for the field if I need to force the alt to stop charging. The way I see it is I wanted no part of a high amperage line running in the cockpit with me and by doing this I cut out some radio noise I had. A win-win.