I plan on initially just having a single alternator, but once I set the plane up for IFR (or start doing a lot of cross country flying), I will probably want to add a backup alternator. I would like that to be a plug and play event vs a big makeover of wiring and firewall work. I emailed back and forth with one of the tech support folks at B&C, which is a well regarded alternator and electronics vendor. They were really helpful in explaining the easiest way to set up a dual alternator system using their internally regulated units (vs externally regulated, meaning fewer boxes and less wiring). I figured out that if I run wiring for a standby alternator switch and put in the nutplates for a second ANL fuse mount, adding the second alternator should be as easy as putting it in place on the accessory pad and wiring it up.
I made a doubler to mount the amp shunt and existing ANL fuse to using AN3 screws. The B+ lead of the primary alternator will go to the ANL 60 fuse, which will then connect to the shunt. When I add the standby alternator (likely a 40 amp, since that's what B&C has for an internally regulated standby unit, even though it's far larger than I'd need for a backup), I'll add a second ANL 40 fuse and the standby B+ lead will go to it. That ANL 40 fuse will then also attach to the shunt.
I offset the mounting location for the two ANL fuses, just to make it easier to route the wires to the shunt without interfering with each other. I probably should have made the doubler a little bigger so I could spread things out a little bit more, but I had already gotten it all drilled to the firewall by the time I figured out that a second ANL fuse would be necessary with the standby alternator.
This doubler attaches to the lower, right side firewall. One screw from the shunt attaches to a nutplate in the doubler, but the inboard mounting screw of the shunt uses a nutplate on the firewall stiffener. I had the fuel fitting doubler done and just sitting there, so I grabbed it and prepped it to be riveted to the firewall. The dimension on the plans won't work though - the top outside corner of the doubler interferes with the start solenoid mount. I ground away a corner of the doubler and riveted it on. After that, I put the washer doubler on the fuel fitting, added some fire sealant and torqued it down.
I attached the nutplates and riveted the doubler to the aft side of the firewall. I also attached the fuel line to the fitting. I torqued it down, but looking at the picture, realize I still need to add torque seal so I know it's been done.
