E-Bus or Main?

[RV7A Flyer]

Originally Posted by rv7charlie

I think the issue they're seeing is the original drawing appears to show an ATC fuse in the 'battery bus' fuse block feeding the endurance bus, and another feeding the main distribution bus.

But the question still stands...assume you're on the E-buss, master buss is off, E-buss fed from the battery buss.

How would a fault in a device or wire on the E-buss blow the fuse *to* the E-buss? Is the assertion that *both* the circuit fuse AND the E-buss fuse blow? or that the E-buss fuse on the battery buss blow before the circuit fuse?

Wouldn't a fault in a circuit simply blow that circuit's fuse?

[az_gila]

Originally Posted by rv7charlie

I think the issue they're seeing is the original drawing appears to show an ATC fuse in the 'battery bus' fuse block feeding the endurance bus, and another feeding the main distribution bus.

Terry, I'm using 'fusible links', as suggested by another poster. But if you prefer, you can use something like a Midi Fuse; designed for high current semi-permanent installations.

The latest version "M" has no fuse, breaker or fusible link shown when the system is in "normal" operation mode.

http://www.aeroelectric.com/PPS/ACAD..._Dwgs/Z11M.dwg

It simply calls for a short - 6 inches or less - 16 g. wire from the Main bus terminal to the E-Bus terminal through the schottky diode.

I still don't see how a item failure on the E-bus can take the whole bus down. If it melts the 16 g wire then the fuse/breaker to the failed unit wasn't sized correctly.

[RV7A Flyer]

Originally Posted by Tbone

I am working on a possible solution for the E-bus protection, but what I'm really asking is as far as distribution of components between the master bus and endurance...The picture shows what items I have. I'm just asking those with opinions.....maybe I should have put this in the PRIMER section! Just kidding. I'm trying to learn something and where a better place than here. Thanks for everyone's input, It's put to good use.

In a sense, the E-buss is just a quick way to shed loads when the alternator goes TU. Just ask yourself what are the absolutely critical items that you would leave on if you had to go through and individually select items to power down one at a time. At night. In weather.

With some minor differences, or preferences, you'll probably arrive at 1 PFD, 1 Nav, 1 Comm, and some cockpit lighting to read paper charts and make notes (without having to hold a flashlight in your teeth). Plus probably the boost pump.

Sequence for operation is E-buss ON, Master and Alternator OFF, and voila! Load shed complete (or nearly so).

[Bevan]

Originally Posted by RV7A Flyer

In a sense, the E-buss is just a quick way to shed loads when the alternator goes TU. Just ask yourself what are the absolutely critical items that you would leave on if you had to go through and individually select items to power down one at a time. At night. In weather.

With some minor differences, or preferences, you'll probably arrive at 1 PFD, 1 Nav, 1 Comm, and some cockpit lighting to read paper charts and make notes (without having to hold a flashlight in your teeth). Plus probably the boost pump.

Sequence for operation is E-buss ON, Master and Alternator OFF, and voila! Load shed complete (or nearly so).

Not only that but the master contactor is shut down saving almost an amp all by itself.

Bevan

[Jesse]

Originally Posted by rv7charlie

I think the issue they're seeing is the original drawing appears to show an ATC fuse in the 'battery bus' fuse block feeding the endurance bus, and another feeding the main distribution buss.

That's my point. I've had fuses blow for no apparent reason many times. Replace the fuse and all is good. Circuit breakers are slow blow. Normal fuses are not. If you get a dead short, the bus fuse could blow before the circuit breaker. That's what I was saying. I wasn't familiar with the Z11 wiring schematic. I was just going by what was in the posted. Having an endurance buscdepend completely on a $0.50 fuse is not my idea of electrical safety, that's all.

[Jesse]

Originally Posted by RV7A Flyer

Or you could just, you know, turn it off.

I'm not saying turn it off. Why would you want your EFIS off? I'm saying not drawing bus current to power it, but rather let it revert to its internal backup battery for the remainder of the flight.

[Tbone]

So...let me get this correct. I'm flying along and need to shut down the system due to a failure of the charging system. I turn off the master and leave on the E-bus switch. Everything that is on the E-bus is now powered directly from the battery bus (12v all time). As drawing Z-11 shows that the voltage that is supplied to the E-bus (when it is used as it is intended) is "fused" by a Blade fuse. If that fuse fails it would remove all those components from the e-bus. Not sure if a "non resettable" fuse is a good idea for such...

Also, as far as the Dynon systems. They have their own backup batteries so should there be a need to have them on the endurance bus?

[Jesse]

Originally Posted by Tbone

So...let me get this correct. I'm flying along and need to shut down the system due to a failure of the charging system. I turn off the master and leave on the E-bus switch. Everything that is on the E-bus is now powered directly from the battery bus (12v all time). As drawing Z-11 shows that the voltage that is supplied to the E-bus (when it is used as it is intended) is "fused" by a Blade fuse. If that fuse fails it would remove all those components from the e-bus. Not sure if a "non resettable" fuse is a good idea for such...

Also, as far as the Dynon systems. They have their own backup batteries so should there be a need to have them on the endurance bus?

That's exactly my point. On the Dynon, I'd want the option of keeping it on the main battery for power.

[rleffler]

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 built mine with a similar mission in mind. I wanted a little more endurance out the Ebus than what you've implemented.

I have batteries on my EFIS as well, but their capacity denigrates over time. So their duration may be unknown when you have a failure. You'll need to periodically test them to understand their capacity. There would be nothing worse to be in IMC and have your EFIS go dark.

I have a RV-10, so I have a little more wiggle room when it comes to weight than in a RV-7. My Ebus is powered by a second Odyssey 680 and a backup alternator on the vacuum pad. I did implement a second fuse block that is dedicated to the Ebus, with a separate fuse for each circuit.

Between the dual alternators and triple batteries, I should be able to handle most situations and make it safely to the nearest airport.

[Tbone]

All good points. I believe I'll move xpndr, alt warning, and dimmer circuits to the main and move at least the D180 to the Ebus. I may also install fusible link to the Ebus circuit or possibly a auto-resettable fuse.