E-Bus or Main?

[Tbone]

I'm finalizing my wiring for the Z-11 wiring "fiasco". I'm having a time trying to figure out what would need to be on the E-bus and what should be on the Main bus. I have studied and researched and on and on and on. I have found out that there is more than one way to skin a cat or panel for that matter. Shown is the ExpressSCH drawing that I have completed and am asking for a critique. Sorry about the excess size....

[rv7charlie]

Hi Terry,

To know what to put on the bus, you need to define the mission. IFR?, night?, EFIS-only panel?, electrically dependent engine?, etc.

In any case, in a real alternator failure emergency, you could do without the transponder.

Charlie

[Jesse]

Is there more than one way to get power to the E-bus? If not, I would certainly not use a fuse to power that bus. Sometimes fuses blow for no apparent reason, and the last thing you want is a blown fuse taking down your whole E-bus in flight, especially in IFR or night, but even day VFR would be bad.

Personally, I despise the use of fuses with a few exceptions. Breakers are not that expensive in the grand scheme of things. If a breaker pops, it's easy to know that it happened. If a fuse blows, you don't know if a fuse is blown, a wire has gone bad or come disconnected or an instrument has gone Tango Uniform. I like using switching breakers for switching, but I especially like breakers for circuit protection.

[RV7A Flyer]

Originally Posted by Jesse

If a fuse blows, you don't know if a fuse is blown, a wire has gone bad or come disconnected or an instrument has gone Tango Uniform.

Does it matter? If a particular circuit goes dark, then any of those 3 mean there's a problem you likely can't fix in flight. If a CB pops, why did it pop? I'd rather deal with the lost piece of equipment later, on the ground, than try to reset what might be a faulty circuit in flight...

To each his own, though...

[Jesse]

But if one of your E-bus circuits shorts, there's a good chance the fuse will blow before that breaker pops, taking out your whole E-bus, not just the bad circuit. Also, some breaker pops are for abnormal issues, and sometimes resetting them works. If it's a dead short it doesn't, but an intermittent short or overcurrent condition may continue working with a reset. Blow a fuse, especially s hidden fuse, and you have no option.

This is one of the reasons I like the VP. It gives a lot more information, like over current, short circuit or even under current (don't know if the VP-X has that last one).

[Tbone]

Yea I see your point Jesse. Just trying to keep close to the Z11 drawings. I'll revisit your point. Very valid. The aircraft will be "capable" of full IFR and night operations. It is full EFIS with no backup other than battery backup wth the Dynon units. Engine is able to operate with no external electrical support due to dual magnetos. Seeing that the mission is defined (at least aircraft wise). Any changes and why?

[RV7A Flyer]

Originally Posted by Jesse

But if one of your E-bus circuits shorts, there's a good chance the fuse will blow before that breaker pops, taking out your whole E-bus, not just the bad circuit. Also, some breaker pops are for abnormal issues, and sometimes resetting them works. If it's a dead short it doesn't, but an intermittent short or overcurrent condition may continue working with a reset. Blow a fuse, especially s hidden fuse, and you have no option.

This is one of the reasons I like the VP. It gives a lot more information, like over current, short circuit or even under current (don't know if the VP-X has that last one).

Why would a single blown fuse on a buss take out the entire buss?

And if I blow a fuse, so what? That single device is now OTS, but everything else will keep working, right? I have two comms, two sources of NAV info (EFIS and GNS), two sources of flight data (primary and backup EFIS) and anything that is single-string, I can keep flying without it. Add in backup batteries and there's no single thing that can go OTS and endanger the flight...

[RV7A Flyer]

Originally Posted by Tbone

Yea I see your point Jesse. Just trying to keep close to the Z11 drawings. I'll revisit your point. Very valid. The aircraft will be "capable" of full IFR and night operations. It is full EFIS with no backup other than battery backup wth the Dynon units. Engine is able to operate with no external electrical support due to dual magnetos. Seeing that the mission is defined (at least aircraft wise). Any changes and why?

I'd recommend figuring out a backup EFIS. I use a Dynon D-6 (also with backup battery), since loss of the primary EFIS would leave you up s**tski creeksy if you were in the soup. At least with a backup EFIS, you could keep the shiny side up and, if your TSO'd nav system were also down, presuming you had some comm capability, you could get vectors to clear air or even a PAR or something...

ETA: On mine: the bare minimum to get down safely in the event of an alternator failure and depleting battery: Fuel pump, 2nd comm, trim, backup EFIS, some cockpit lighting, and the cigarette lighter adapter (e.g., for a handheld comm). Given the backup battery in both EFISes, I can use that for the primary (good for about 1 hour), and that gives me GPS nav data as well.

What is "ALT LIGHT", and why is that on your E-buss?

[Tbone]

I see Jesse's point. If you lost your power through the main bus (per power shut down), you would be powering your E-bus items through the battery bus. Your E-bus is supplied through that bus by a ATA fuse. Now if I fuse that with an appropriate fuse, or thermal fuse, it should be feasible. Yes?

[Mich48041]

Bob Nuckolls once wrote, That fuse that blew or that breaker that popped might have prevented an electrical fire. Do you want to give it (the fire) a second chance?