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Electrical Buses

We maxed out a VPX Pro and still have 16 circuit breakers for our Ebus. It is a little disheartening when you try to consolidate with the latest tech and still end up having to put an array of old school CBs in your panel because the new tech can't do everything.

Wow. VPX and 16 breakers!
In my RV-8 (dual screen SkyView HDX, GTN-650, Dynon radio, XPDR, dual axis autopilot, ADS-B receiver and all the associated bells and whistles like USB ports, pitot heat, nav/strobes, landing and taxi lights, etc. I use twenty pull breakers (three are installed spares) and seven switch breakers (one is an installed spare).

Carl
 
Wow. VPX and 16 breakers!
In my RV-8 (dual screen SkyView HDX, GTN-650, Dynon radio, XPDR, dual axis autopilot, ADS-B receiver and all the associated bells and whistles like USB ports, pitot heat, nav/strobes, landing and taxi lights, etc. I use twenty pull breakers (three are installed spares) and seven switch breakers (one is an installed spare).

Carl

Remember to set SCE to AUX...
 

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Wow. VPX and 16 breakers!
In my RV-8 (dual screen SkyView HDX, GTN-650, Dynon radio, XPDR, dual axis autopilot, ADS-B receiver and all the associated bells and whistles like USB ports, pitot heat, nav/strobes, landing and taxi lights, etc. I use twenty pull breakers (three are installed spares) and seven switch breakers (one is an installed spare).

Carl

How many does the VPX accomodate?
My typical panel has about 15 brkrs and 10 slot fuse panel.
 
lr172, you bring up a good point. I think you are correct about the general range of required RPM. This is something to be aware of.

For this to scenario to play out though and actually to be a concern you would have to:

1) Electrical failure (Possible / Likely at some point)
2) Reduce the power to idle early enough to be problematic (Avoidable if known)
3) Then need to do a go-around for example (Possible)

Certainly knowing the limitation of the PMAGs generator capability this could be avoided.
 
P-mags

If KISS is your goal, maybe it looks like this. & remember most EFIS systems have their own internal BU batteries.
Check the P-Mag manual, it suggests it would be operational anything above 900 rpm & sufficient to land without outside power.

That's pretty close to what AFS recommends. Basically a fused or breaker circut from the Master Contactor inside to the switches then back out to the P-Mags.
Now if it were IFR that would be a totally different rabbit hole an another 100 lbs of stuff! :D
 
VPX-Pro Circuit Number

How many does the VPX accomodate?
My typical panel has about 15 brkrs and 10 slot fuse panel.

I am installing a VPX-Pro in my all-Garmin RV-7 project, with dual G3X screens, a G5, XM radio receiver, a full suite of Garmin LRU’s, electric trim, GTN650Xi, GNC255A, GMA245R audio panel, GTX45R transponder, TCW IBBS backup, the typical strobes, landing lights, interior lights, USB charging outlets, etc.

I am also installing dual PMAGS. The VPX-Pro installation manual expressly states that the VPX-Pro is designed to power PMAGS if the builder desires.

A VPX-Pro has 32 switched circuits. I will not max that out in my RV-7 installation.

Without seeing the actual design of the system referred to in the previous post, I am probably missing something. But it would seem that 32 VPX-Pro switched circuits, plus an additional 16 circuits requiring conventional circuit breakers would mean somewhere around 48 circuits.

I fully support the idea that everyone in the EAB world has valid individual reasons for designing an electrical system to suit their personal preferences. Furthermore, I definitely recognize and support that there are valid reasons pro and con for using conventional CB’s vs. Vertical Power or Advanced Flight Systems ACM electronic circuit breakers. So I have no interest in that ongoing and largely irrelevant to me debate.

I have already made my choice.

That said, based on my RV-7/VPX-Pro project (which I joke has turned into a demo platform for every Garmin product out there), an RV-7 electrical system design using 32 VPX-Pro circuits, and requiring an additional 16 conventional CB circuits, arouses some level of curiosity. It would seem to offer some additional features the builder views as enhancements that are not present in a more typical VPX-Pro installation like mine.
 
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Seems like this thread went to sleep about a month ago, but I will see if I can re-light it... So many good points made in the many posts.

It's important to consider total system architecture in a bus-count discussion, so when designing the electrical system for my RV-7A, my thought process went like this:

Mission
Architecture
Busses

Mission: Light IFR (as previously mentioned, punching thru cloud layers to get in & out)
Architecture: Redundant power sources. In my case 2 batts, 1 alternator
Busses: 1 bus, UPS style feed (more on that later)

It is my understanding that the main idea behind the "traditional" Main/E-Bus architecture was to facilitate load shedding in an emergency to increase flight time after alternator failure.

As Iron Flight and others have observed, with today's avionics & LEDs, the typical load is under 10 amps in many cases so load shedding becomes less of an issue. And any load shedding can be accomplished by pulling a couple of breakers. I don't think it warrants the complexity of having multiple busses.

Based on all that (and without writing a book) here is the design I came up with for my airplane. I call it a Single Bus, 2 Battery with Uninterruptable Power Supply circuitry.

Again, trying not to write a book here, so picture worth 10,000 words. Please see attached...

-Jeff

PS - A note about this drawing: It is not intended to be a wiring diagram or show all minute details. It's a schematic whose purpose it to depict the circuitry for design & analysis.
 

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The PDF file I attached to my previous post shows up as a black rectangle so here is a PNG that will show up as a regular thumbnail image...

OK, that's better ;)
 

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<Snip> It is my understanding that the main idea behind the "traditional" Main/E-Bus architecture was to facilitate load shedding in an emergency to increase flight time after alternator failure.<Snip> [/QUOTE said:
This is a very common perception but as I understand it one of the main reasons for an e-bus is to allow the master to be switched off, thus removing the load required just to hold the master contactor closed (between 1/2-1 amp I believe)

Bob Nuckolls dubs the e-bus the "Endurance" bus. Its purpose in his designs is to preserve battery power during cruise flight after alternator failure, so that power is available for landing. Thus items not used in cruise such as flaps and fuel pump
are not intended to be on the e-bus in Bobs designs.

Of course missions and objectives change but I do think that these basic principals of Bob Nuckolls electrical designs are frequently overlooked.
 
Lot's of different views of what needs to be or should be on the endurance bus. It really depends on the person and what they feel comfortable with. To me things that can be switched off or maybe even that are normally switched off such as a fuel pump or flaps are fine to be on the bus. You can always make the decision not to use the fuel pump or the flaps if they are on the endurance bus. If they aren't you have no options.
 
Ed,
You can get a Gigavac GV200 which has substantial lower current draw that traditional master relays, so you can run single bus, not to mention they are an amazing, quality piece of kit.

Cheers,

Tom
RV-7, IFR single bus with backup batteries in G5 and Aera 660
 
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