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EFII/Bus Manager/VPX Primary Layout

sbalmos

sbalmos

Well Known Member
Hi all,

Posting as a new thread here so that I don't pollute the original EFII thread. Attached, by popular request, is my pencil-to-Visio conversion of my designed primary power bus. This was written up at Oshkosh with input from Chad. I'll open it up now to the forum at large for comments, possible improvements, etc. Hopefully it doesn't diverge to a flame-out.

http://sbalmos.fastmail.fm/Primary%20Power%20Bus.pdf

Some notes of what I did/found:

  • Because the Bus Manager's Essential Bus is running everything ignition and primary avionics, Chad and I agreed there was no reason to go VPX Pro
  • I am adding a "Fuel Pump Master" switch, so that one can have on the essential avionics and also the ECUs for programming, without having the rest of the ignition system "hot"
  • The push-button starter I am still hanging off of the VPX, to make use of the starter enable ability. This still wires to the starter switch pins in the Bus Manager. This may be a point of contention, but I don't mind re-enabling the Main Bus to start
  • I leave the GTN 650 as an essential piece of avionics because selfishly I want it to be COM 1, which is the only thing cut-through in the audio panel if power is killed to the audio panel. And also I can do a full instrument approach by hand if necessary in an essential power situation.
  • Obviously not every detail is shown, but this is the master main layout I'm going off of

Thanks for any considerations all.
 
EFii power

Hello Scott,
Your drawing may have been simplified on purpose, but I see three circuits I would consider making six. Your drawing has two fuel pumps on one breaker, two coil packs on one, and two ECUs on one. If the breaker pops you will loose both systems. I would consider placing each of these essiential items on an independent circuit breaker.
 
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Understood Marvin. I'll consider it when the brain is idly staring at it next time. A few things though:

  • The EFII Bus Manager only enables one fuel pump at a time, thus the relay.
  • The ECUs themselves only draw 0.1A each (I'm actually considering dropping that breaker down to a 2A one for that reason). The potential for them to run away and pop the breaker is, IMO, tiny
  • The coils are the only thing I can think of that might be good to have on separate circuits, since they have separate power switches already.

And I just realized that my over-simplified drawing at the top is missing alternator field lines and an enable switch for each. There should also be starter solenoid enable lines from the Bus Manager to each solenoid, but Visio is not cooperating in line routing.
 
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Keep in mind that breakers and fuses are there to protect wiring, not the end device. If a wire or device shorts, the breaker/fuse does its job to avoid a potential fire.

I agree with everything M McGraw said and would add that you could use an inline fuse on the Accessory USB and use that slot in the VPX for something more critical.

I also thought the flap motor pulled more than 5 amps but could be wrong.
 
sbalmos said:
The EFII Bus Manager only enables one fuel pump at a time, thus the relay.
Click to expand...

You missed Marvin's point. You have both fuel pumps on one fuse. If the running pump or the relay feed shorts to ground, you lose both pumps and become a glider.

Coil packs and ECUs; if either device or any part of the wiring shorts to ground, you're a glider.

Why have a fuel pump switch ahead of the relay? An EFI'd engine doesn't run unless a pump runs. You'll always have one pump ON. The task is merely to select which one.

You're already carrying around two complete electrical generating and storage systems. Why not feed two independent busses, each feeding one ECU, coil, and pump?
 
DanH said:
You're already carrying around two complete electrical generating and storage systems. Why not feed two independent busses, each feeding one ECU, coil, and pump?
Click to expand...

Yep..............

And, about the second starter solenoid.....?????????
 
Dan / Mike - while I don't disagree in principal, most of my response at this point is because the design is based on requirements and the output design of the Bus Manager. Please see its manual, http://www.flyefii.com/bus_manager/Bus_Manager_Installation_Instructions.pdf. It is the Bus Manager that requires two starter solenoids. It is the Bus Manager that drives the relay, that selects which one of the two fuel pumps is on - and is fed by a single fuse/breaker upstream. There is no concept of a second independent essential bus.

Initially, instead of having a "Fuel Pump Master" switch, Robert said I should just pull the fuel pump CB if I wanted to run my essential avionics on the ground for programming without running the pumps. Personally, I don't like fooling with my breakers (I don't even like having physical breakers, but that's a whole other debate).

As I said, I will consider separating the ECU and coil pack breakers. Everything else mentioned is subject to the constraints of the Bus Manager.
 
sbalmos said:
It is the Bus Manager that requires two starter solenoids. It is the Bus Manager that drives the relay, that selects which one of the two fuel pumps is on - and is fed by a single fuse/breaker upstream. ----------------------------------------Everything else mentioned is subject to the constraints of the Bus Manager.
Click to expand...

OK, didnt realize all that from your original drawing, ------ missing wiring from Buss Mgr.
 
Yeah, it's sort of implied by the pump selector switch hanging off the Bus Manager. Sorry. There's a number of other wires that should be hanging off of the Bus Manager - one to the pump relay, starter solenoid enable lines, etc. Showing those, which I sort of consider signal wires for this drawing's purpose, and I'd be locked in a debate with Visio over who can form the longest expletive-laden phrase that still made sense. :eek:
 
sbalmos said:
Dan / Mike - while I don't disagree in principal, most of my response at this point is because the design is based on requirements and the output design of the Bus Manager.
Click to expand...

Doesn't change the facts.

Pump circuit is Drawing 3 in the linked PDF; the feature is sold as automatic pump switching. If fuel pressure drops (as measured by the EIS pressure sensor), the black box circuitry grounds the gray wire, connecting power to NO.

Ok, short any part of the 16 ga wire between NC to pump 1, or between and the panel warning light, or short the pump internally. The 10 amp breaker trips open.

The magic box sees the fuel pressure signal heading for the cellar, so it grounds the gray wire. However, nothing happens, as the breaker remains tripped. The engine gets quiet.

Pilot eventually finds the tripped breaker and resets it. Or maybe not. Either way, it's not automatic, nor is it a customary pilot response. If you think it unlikely, consider that the "shorted wire" scenario is why we install fuses or breakers in the circuit.

Now consider a simple dual bus system, with the requirement that two pumps cannot run at the same time. Each pump is fed from an independent bus, and has its own breaker or fuse.

Plan A simply has two pump switches. An LED flashes if pump #2 is engaged, just so the pilot doesn't run it inadvertently. A failure of pump #1 (and an EIS fuel pressure warning) requires a pilot action...switch on #2. It's the same action we take now to cure a fuel pressure loss with a carb or constant flow fuel injection, so it works for any pilot...no special system knowledge required.

The reason two pumps should not be run at the same time is fuel pump cooling. Without enough flow, an electric pump may overheat. A simple mechanical plan B might add a second pressure regulator in a line tee'd from the outlet of pump #2 to the tank return line, which may or may not need to be slightly larger. Pump #2 can now be turned on during takeoff and landing, then turned off at altitude, again just like a regular 'ole RV.



If you must keep your Bus Manager, consider the SDS ECU's pump control output. It's intended to drive a pump relay so that if the engine stops, the pump stops. You could hotwire a pump #1 relay from a battery source, and control it with the ECU. That would leave the essential bus power source and Bus Manager backup switching to operate pump #2 exclusively.
 
sbalmos said:
  • I am adding a "Fuel Pump Master" switch, so that one can have on the essential avionics and also the ECUs for programming, without having the rest of the ignition system "hot"
Click to expand...


  • Not a bad idea, what I did was run 2 separate CBs (one for each fuel Pump) AFTER the full pump relay. The essential bus, which is the most protected of my 4 bus's, feeds the really then the power goes to two separate breakers on the way to the pumps. Not completely impervious, but more so, I thought
    sbalmos said:
    [*]I leave the GTN 650 as an essential piece of avionics because selfishly I want it to be COM 1, which is the only thing cut-through in the audio panel if power is killed to the audio panel. And also I can do a full instrument approach by hand if necessary in an essential power situation.
    Click to expand...

    Did the exact same thing... I have mine also running on TCW back up battery. Since it's on during start up, this helps provide "Sag" protection.


    [/QUOTE]

    DanH said:
    You missed Marvin's point. You have both fuel pumps on one fuse. If the running pump or the relay feed shorts to ground, you lose both pumps and become a glider.
    Click to expand...
    Yep, that's why I did separate breakers. At least it's one more step of protection in my book

    DanH said:
    Coil packs and ECUs; if either device or any part of the wiring shorts to ground, you're a glider.
    Click to expand...
    I have the 2 ECUs on separate bus's and separate breakers. the ignition and fuel are on the essential bus, which, by design has a lot of redundancy to it
    DanH said:
    Why have a fuel pump switch ahead of the relay? An EFI'd engine doesn't run unless a pump runs. You'll always have one pump ON. The task is merely to select which one.
    Click to expand...
    The way the bus manager is set up, and the way you set up the fuel system is, you set the fuel pressure to a desired point in which if Pump# 1 isn't hitting that pressure, pump #2 will kick on. I have Annunciator lights to let me know which pump is running. The one for #2 is amber, kind of a "hey, something's up, hey want to think about doing something about it"

    DanH said:
    You're already carrying around two complete electrical generating and storage systems. Why not feed two independent busses, each feeding one ECU, coil, and pump?
    Click to expand...
    This is what I have set up (kind of) except for the pumps. You'd have to redesign something to incorporate the auto/relay function if you separated the power. I'm sure it's doable
 
Rev B has been uploaded with further clarifications, now that I seem to have gotten Visio under control. A few more breakers, as has been suggested. And despite what the original drawing showed, no, I wasn't actually powering the ECUs, ignition, and pumps through the LEDs in series. I cannot find definitive information at the moment on how much the flap motor pulls. But the two other electrical drawings I've been using, both RV-10s, have the flap motor behind a 5A breaker. So the idea that the flap motor draws >5A seems to be incorrect.
 
How about feeding one ECU and one coil pack from buss one and one ECU and one coil pack from the essential buss. That's the easy fix. Now, If you power the fuel pump relay through a diode (to prevent reverse current) you can then run power from buss one through a Switch and breaker to pump one. You can run a separate one from the essential buss through a Breaker and switch to pump two. This gives you the option to manually select power to an individual pump in the event the 10 amp pump breaker fails or will not reset due to a short to ground. Does this sound plausible to you electrical gurus?
 
John,

The flap circuit is capable of 10A. You can set it to 5A then adjust to 7A if needed.

Why are the trim circuits on the same circuit as the flaps? Trim motors have their own dedicated circuits on the VP-X, as does the flap motor.
 
Marc,

Unsure, as I was basing off of a few other drawings as previously mentioned. Both of the ones I have here at the office show the trim & flaps on actual breakers. Presumably I guess just for electrical load planning. I've updated to Rev. D to clarify this. In a separate spreadsheet where I'm doing the actual per-wire interconnect planning, I already had the trim motors and flaps connecting to their dedicated lines on the VPX. Nice talk at Oshkosh BTW.
 
Alternator switch

sbalmos,

Have you thought about installing a DPDT switch in lieu of your two SPST alternator switches? That way you can only activate one alternator at a time. The DPDT switch can have an off position in the center.
 
Paul,

In the dual alternator Bus Manager setup, the charging circuits are independent. It is intended that both alternators be enabled during normal operation. I just confirmed this with Robert this morning, just to check my own sanity. Had to double check, because I know RVs usually have a manually-enabled backup alternator. But I'm used to some certified planes, namely Cirrus, that have dual independent alternators that are meant to both be enabled.
 
Scott,

I believe that you are correct for your application. I am designing mine at the moment and it is very similar except that I am installing one battery and two alternators. I will be installing a switch that will allow only one alternator to be active at a time so that they are not competing with one another.
 
One batt two altenators

219PB said:
Scott,

I believe that you are correct for your application. I am designing mine at the moment and it is very similar except that I am installing one battery and two alternators. I will be installing a switch that will allow only one alternator to be active at a time so that they are not competing with one another.
Click to expand...

Paul,
Do you have the latestest copy of The Aeroelectric Connection? If so, figure 17-8 has a backup alternator on the same buss as the primary Alt. The backup is set to 1 volt lower than the primary so that it does not conflict. If the primary alt fails the backup picks up the load automatically and turns on an indicator in the cockpit to advise the pilot. I think this setup would still require a small second battery to prevent EFIS brownout during starting. I like the concept, but I have no experience with it and am hoping someone on this site could provide a pro vs con.

P.S. - Moderators would it be possible to make this a seperate thread so I don't hijack Sblamos?
 
Marvin / Paul,

I don't mind, if the mods don't. Paul, I'm assuming at this point that you're *not* using the Bus Manager. It requires dual batteries. This prevents the brownout conditions during cranking that you would otherwise solve with an EFIS-local TCW battery. Otherwise, your comments and Marvin's notes about alternator switching and voltage differences is correct. In my case, specifically because the Bus Manager isolates the two charging circuits, I went with the alternate (hah) backup alternator, the FS1-14B variant of Plane Power's FS1-14. The regular -14 outputs at the usually-necessary -1V of nominal, whereas the -14B outputs at the full 14.2V.
 
I am looking to incorporate the Bus Manager with the VPX Sport and a Skyview. The Skyview has the backup battery so it will not brownout during cranking. I am adopting going with a second alternator only. This will save the weight of the additional battery. The tricky part of looking at these systems is determining what if the VPX or the Bus Manager fails. You can have the VPX automatically switch to the backup alternator. They recommend using a full 14.2V alternator. I wonder if the alternator has a better capacity if it outputs with the additional 1 volt. It would stand to reason. If an alternator failed in flight I would not consider that an event that had to be controlled automatically. The Dynon would alert me of low voltage and I would switch alternators. I also want all items that need to be performed as part of the startup and runup checklist to be outside of the EFIS. I do not mind reading info off of the screen but I do not want to be navigating menus.
 
Scott or someone else that might know,

What is the best way to post a pdf file? I see that Scott must have his own server to host the pdf link that he has. I understand how to link photos to the forum but are there sites that will allow a pdf to be hosted there?

I have followed Scott's thread and have made my electrical schematics and would like to post it for discussion.

Thanks,

Paul
 
Dropbox, Google Drive, Microsoft OneDrive, others, take your pick. :) They all, under some name, will provide a public/sharing/etc link to a file stored there, like a PDF.
 
Scott, I don't see power for your fuel injectors on your schematic. Is the power provided by the controlling ECU or is it somewhere else?
 
Sorry, injector power is not listed. It is hanging off of the same breaker and switch for the fuel pumps.
 
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