Dual master solenoids?

[tomhanaway]

Working my way through Nuckoll's Z-13 wiring diagram.
I'm building an 8-a VFR with single battery, single alternator.

I'm not excited about the use of his "always hot" main bus because of the additional wire runs it would create from the buss mounted close to the rear mounted battery and difficulty accessing fuses for those wires.

I'd like to run all electrical busses from the always hot side of the starter solenoid (always hot when master solenoid is hot).

Given this scenario, it seems that the really significant system weakness is the failure of the master solenoid. I was thinking that a second master solenoid, with a separate wire and switch, wired in parallel at the battery, would address this issue.

Does this make sense or am I missing something obvious (or not so obvious)?

Thanks,
Tom H.

[Low Pass]

Imo, the classic/Nuckols design is a good balance of simple and reliable.

I have a single master, single starter solenoid (the one on the starter). Knowing what it does to you when the master fails - open or closed - I replace mine with commercial quality White Rodgers every 3 years, as I do the alternator (Nippon/Suzuki). Never had one fail in 14+ years.

Follow up thought on simplicity versus redundancy. The absolutely wonderful thing about our EAB world is that we can do either. I've tried both and now always go with simplicity. My concern is having something fail on a trip. (Non life threatening situation. E.g. partial electrical failure in VFR conditions.)

So, there you are. Half way to your destination on this nice trip you've planned, and one of your backup or redundant components fails. You going to continue? Your buddies are waiting. You have a spare/backup installed, so just go. Right? Most I know would either stop or alter their trip because something broke. You have two ignition systems. One quits, you going to continue? (Yea, I know - higher criticality system.) One of your installed redundant electrical power devices fails. Going to continue?

With these added devices you have now increased the probability of something failing. (Twin engine planes are twice as likely to have an engine failure as a single!) And that's assuming operationally the system is tolerant of a parallel component failure.

Just a thought. Not knocking anyone's choices.

[Mark Dickens]

What I did was run my e-buss power directly from the battery through an e-buss master switch. No contactor involved. I also have a B&C vacuum pump mounted backup alternator for charging the battery in that scenario. The B lead runs directly to the battery. None of this will ever be used unless the primary alternator or the master contactor or the VP-X fails. My battery is mounted forward in the RV-8 baggage area so there aren't long wiring runs for any of this.