Still playing with the firewall layout

Well, the work ethic still hasn’t been great, but I keep trying to chip away. Over this past weekend I did some more poking around with how to lay out firewall stuff. Deciding on the battery box position and orientation was helpful, but there was still the question of other electrical stuff. Specifically, I also need to locate the master and starter contractors, the ammeter shunt, a big fat ANL fuse to protect the alternator B-leads as well as the supply line to the fuse blocks inside the cockpit, plus the battery bus and e-bus relay.

Basically, there’s a bunch of stuff here and a lot of considerations. I’d like to avoid placing anything so that it’s a huge pain to access for service. At one point I was considering locating the ANL holder and shunt inboard of the battery box, but that would mean that if that big ANL fuse ever popped, I’d have to pull the whole cowl and probably crawl under the airplane to service it.

The contactor locations, at least, were straightforward: I can place both of them just above the battery box. The battery bus and e-bus relay can probably go basically anywhere; they barely weigh anything and thus I don’t need to worry a lot about the structure they’re attached to. But positioning that ANL holder and shunt was giving me fits.

I eventually arrived at a somewhat obvious solution – namely, neither of those need to be mounted to the firewall. And since they’re both sort of oblong pieces, each with two large screw holes, they’re good candidates for just mounting on an engine mount tube with adel clamps. I tried a few different spots, and for the moment they’re living on one of the upper tubes. I think this location should be good, though one of the fun things in the back of my head is where lots of other wires and things are eventually going to be routed.

Still, I feel good enough about this to go ahead and work on the mount plate for the battery box and contactors. I think the biggest obstacle for that is going to be getting over my reluctance to go drill holes in the firewall, but it’s got to be done.

I also did some other tinkering along the way; for example, I wanted to have some general mental picture of where the fuel and oil lines to the pressure sender manifold would live. That required some digging into plans and researching. (example: where does the oil pressure sender line even connect?)

In any case, I think this is the point where there’s nothing for me to do but to pull the engine back off and get going on that battery mount. I’ll also want to drill the holes for the control cable passthroughs while the engine is out of the way. One of these evenings I’ll work up the wherewithal to do it…

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