Battery Bus - before the Battery Contactor

[OneTallShort]

I would suggest that Bob Nuckolls has different wiring diagrams for electrically dependent aircraft (ECM) engines, specifically Z-19 with the "Engine Battery Bus". In these designs, there is a backup battery bus (and contactor) in addition to the primary bus. Z-11 still has magnetos with optional (aux) electronic ignition.

More information on this bus can be found in The AeroElectric Connection Z-29 "Battery bus" diagram. This bus is not intended for electrically dependent ECM engine operation, but IS for the always on equipment or items that you want independent of the main battery contactor. The MGL EFIS "Keep alive" power that keeps the coin cell from being depleted is a perfect example of this use. The cooling pump circuit for the Turbo is another Sonex specific use, which is designed to run after shutdown and with the master off. And "bus" sounds more official than most of the typical field wiring installations of this equipment, but if you want electrical equipment on when the master (bus) is off, then it goes on this part of the circuit. If you think about automobile electrical design, this is extremely common...all that equipment that works when the key is off. Not saying that we should copy everything from auto design, but there are a lot of similarities.

It's also important to understand that most Battery bus equipment has additional switches in the circuit. For example the Hobbs meter has a oil pressure switch on the ground side. The electronic ignition also has it's own switch. Just because the equipment is directly off the battery before the contactor doesn't mean that it can't be shut off. The EFIS keep-alive circuit is probably the one exception to this rule, but it's still fused.

I would also say that Bob's point is that anything on this part of the circuit needs some type of protection close to the battery from a direct short...either a fusible link, or a fuse. Either will work. See The AeroElectric Connection page 10-4 where he discusses the use of fusible links. Using inline fuses on the firewall side is also pretty typical for these connections as Rynoth showed in his post.

I'd also suggest looking at the 001-510 B&C wiring diagram as a good simple starting point for a Sonex wiring diagram.
https://bandc.com/wp-content/uploads/2018/05/001-510_vfr_single_alt.pdf
I'm not sure if this is a Bob Nuckolls' diagram, but it certainly reflects his other designs, and is a bit cleaner than the Z diagrams with updated B&C parts.

Gregg Short
Burbank, OH
Sonex N715SX