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EFII Bus Manager

TXFlyGuy

Well Known Member
How many here are flying with the EFII Bus Manager? It looks pretty good, and actually is similar in some ways to the auto-bus tie switching we have on Boeings.
I contacted the company, and their claim was they have never experienced a failure of the bus manager.

What is your experience?

http://www.flyefii.com/products/bus-managaer/
 
If you have an electrically dependent a/c (engine, and/or, if IFR capable, panel), get an actual schematic of the box's guts & analyze failure modes.

There was an extensive discussion on the Aeroelectric list recently.
 
The company claims no failures. It does have an emergency selector to manually select a battery to power the essential bus in the event of a failure.

No one here flying with this?
 
I have one; and my -7 requires electrons to keep the engine running.
I had a problem with the Fuel pump switch-over circuitry during the initial testing after install. The problem was was taken care of perfectly by EFII.

I'm happy with it and if I could make any changes, it would be to add an "off" positions to the fuel pumps. (as it stands you can only switch between "1/auto" and "2".) I may add something to the switch/relay circuit sometime in the future to take care of that.
 
I have one; and my -7 requires electrons to keep the engine running.
I had a problem with the Fuel pump switch-over circuitry during the initial testing after install. The problem was was taken care of perfectly by EFII.

I'm happy with it and if I could make any changes, it would be to add an "off" positions to the fuel pumps. (as it stands you can only switch between "1/auto" and "2".) I may add something to the switch/relay circuit sometime in the future to take care of that.

Thanks. Our flight testing is a few months down the road. Good to hear that EFII gave you good support.
 
Buss Manager Concept

I've essentially installed my own design of this concept, and for a LOT less $$$. My aux fuel pump has OFF - AUTO - ON selection modes.

How many here are flying with the EFII Bus Manager? It looks pretty good, and actually is similar in some ways to the auto-bus tie switching we have on Boeings.
I contacted the company, and their claim was they have never experienced a failure of the bus manager.

What is your experience?

http://www.flyefii.com/products/bus-managaer/
 
Dual EFII, I went with all manual high quality switches, my HDX will alert me if fuel pressure or volts get low, then I just confirm and flip a switch, BU pump, ECM, or battery. KISS!
 
That's one of them. IIRC, there's one where at least a 'flow chart' type internal diagram was posted. One of the 'selling points' was that it auto-managed power source switching in a multi-alternator and/or multi-battery system. That's the primary thing that bothered me (give failure analysis of *that* some thought...), though the fuel pump management issue is obviously significant, as well.

Everything's a compromise (except the exception we can't discuss), and everyone's got to pick their priorities on which tradeoffs to accept.

Charlie
 
Just heard back from the manufacturer. To date, the EFII Bus Manager has had zero failures in the field. None.

And, if there was a failure, the installed emergency power switch will restore battery power to the essential bus, keeping that engine making noise.

Zero failures...well, since I have been flying turbojet powered aircraft (1987-present), I have experienced zero engine failures.

The fact that the bus manager auto-manages power selection does not bother me. Just like the auto bus-tie relays we have on the big Boeing.
 
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The Bus Manager is a fun little box that does a number of things.
Most importantly, it provides two separate current paths to the engine electronics that do not require pilot intervention to manage.
The emergency power switch is a third level of redundancy on top of that.

We have many smart customers who have their own idea of how they would like to implement their electrical power distribution. I have reviewed many of these designs over the years. It's usually a bit amusing, because once someone gets a good design figured out, it usually looks a lot like the Bus Manager. Then they purchase a Bus Manager and move on.

For most experimentals, the Bus Manager can serve as the power distribution for the entire aircraft. The Main Bus output powering non flight critical systems and the Essential Bus output powering the critical engine systems. It can provide a drastic simplification to the task of implementing the aircraft power distribution.

We have close to 200 Bus Managers in the field. The only one that ever had a bus failure had one of its bus outputs shorted directly to ground during installation. (turn the power off when doing the wiring!).

They are over designed, very robust boxes. They have an internal cooling fan to limit the thermal range of the power components. But the box doesn't need the cooling fan and is thermally stable without it.

The fuel pump management is a great feature and works very nicely.

The main thing we are concerned about with electronically dependent engines is the protection of the 12v supply to the engine electronics. A wire coming loose at your battery is a simple fault that could happen to anyone. The Bus Manager keep the engine running in this case and in many similar cases.

The majority of our experienced installers who are familiar with our system put in a Bus Manager with every EFII installation. It's a low cost simple solution that provides lots of protection against electrical faults.

Robert Paisley
 
The Bus Manager is a fun little box that does a number of things.
Most importantly, it provides two separate current paths to the engine electronics that do not require pilot intervention to manage.
The emergency power switch is a third level of redundancy on top of that.

We have many smart customers who have their own idea of how they would like to implement their electrical power distribution. I have reviewed many of these designs over the years. It's usually a bit amusing, because once someone gets a good design figured out, it usually looks a lot like the Bus Manager. Then they purchase a Bus Manager and move on.

For most experimentals, the Bus Manager can serve as the power distribution for the entire aircraft. The Main Bus output powering non flight critical systems and the Essential Bus output powering the critical engine systems. It can provide a drastic simplification to the task of implementing the aircraft power distribution.

We have close to 200 Bus Managers in the field. The only one that ever had a bus failure had one of its bus outputs shorted directly to ground during installation. (turn the power off when doing the wiring!).

They are over designed, very robust boxes. They have an internal cooling fan to limit the thermal range of the power components. But the box doesn't need the cooling fan and is thermally stable without it.

The fuel pump management is a great feature and works very nicely.

The main thing we are concerned about with electronically dependent engines is the protection of the 12v supply to the engine electronics. A wire coming loose at your battery is a simple fault that could happen to anyone. The Bus Manager keep the engine running in this case and in many similar cases.

The majority of our experienced installers who are familiar with our system put in a Bus Manager with every EFII installation. It's a low cost simple solution that provides lots of protection against electrical faults.

Robert Paisley

Robert: Thanks for the information. Good stuff to know when you are tooling along IFR, getting ready to shoot an approach to minimums.
 
Most importantly, it provides two separate current paths to the engine electronics that do not require pilot intervention to manage.

Bull. It drives a main and essential bus. There is no power path dedicated to engine electronics alone, and pilot intervention can be necessary.

The emergency power switch is a third level of redundancy on top of that.

The emergency power switch merely bypasses one of the Bus Master's relays. The only failures it can directly mitigate are the relay or the relay control circuits. As the key switch controls both main and essential relays in parallel, the real purpose of the "emergency"switch is to provide a way to shut down the main bus and still have power to the essential bus. Put another way, it's not a backup. It is required.

For most experimentals, the Bus Manager can serve as the power distribution for the entire aircraft. The Main Bus output powering non flight critical systems and the Essential Bus output powering the critical engine systems.

So, both ECUs and both ignitions are powered from a single essential bus, not the claimed "two separate current paths". Let's put a smoke smell in the cockpit. With the main bus shut down (key OFF), the only power path is through the "emergency" switch. Can't check that switch on the run up pad without shutting down all the main bus avionics, so it won't get checked very often, which kinda stomps a basic rule about checking equipment required for flight.

We have close to 200 Bus Managers in the field. The only one that ever had a bus failure had one of its bus outputs shorted directly to ground during installation. (turn the power off when doing the wiring!).

Which nicely defines one of many failure modes. Or are we to believe that the same output can never get shorted in an airborne aircraft? When it happens, it's essentially a dead-shorted battery, so it melts the Bus Master's diodes, and/or relay(s), and/or "emergency switch", none of which are rated for anything like battery amperage. BTW, the switch requires running an unprotected 10 ga lead into the panel, and then back to the BM. Does that architecture increase the risk of a short?

There is no master solenoid near each battery. The large cable runs to the BM can't be disconnected. Same for the cables to the start solenoids. Stuck start solenoid? Sorry Charlie.

The fuel pump management is a great feature and works very nicely.

Both pumps are driven by the same single wire, breaker, and relay. A shorted primary pump annunciator circuit, a shorted pump power circuit, or a shorted pump motor will all pop the circuit breaker. Of course the BM will detect the loss of fuel pressure, but the "fully automatic pump management" can't make the second pump run until the pilot diagnoses the cause of his no-run condition, then finds and resets the circuit breaker. Good luck with that at 300 feet outbound over the trees, where the rest of us are simply running two very independent pumps.

BTW, the BM diagrams all use the standard diamond symbol for grounds, with no further details. The BM has a single ground; loss of that ground path opens the relays and makes everything silent. Restoring power will require diagnosis time, then finding and flipping the emergency switch...more fun out over the trees.

The text suggests grounding everything to a single point ground bus. Drawing 1 ties the ground bus to the batteries with a single 4 ga cable in parallel. I recently proposed something similar for my own airplane, and the gang quite correctly pointed out that terminal corrosion at the one shared battery negative post has the potential to shut down both ignitions. That is also true here, at Battery 2.

I can go on, but hopefully the point is clear. There is nothing very redundant about a Bus Manager, and it brings failure modes of its own. Some are not recoverable. Others require time and pilot input not always readily available.
 
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Wonderfull propaganda effort Dan - bravo!
It's going to take awhile for my Internet bologna meter to unstick its needle.

If any Actual customers have any Actual questions about how our products Actually work, please contact us directly.

Thanks,
Robert
 
Love mine

I'm flying it... see my write up on my first 100 hours with the EFII system.
Really simplified my electrical system wiring. It's essentially a Bob Knuckols design in a box.
With 2 alternators and two batteries feeding the buss manager, I've got a fair amount of protection.
Sure, could you use relays, and shotki diodes and build the same thing, but this is all done for you. Read Aero electric connection and look at the examples in the back. I can't remember which one this is a replica of..

And yes, I do test my emergency switch periodically. It's so stupid simple that there's not much to go wrong, and since all my avionics are on their own back up batteries, not much changes in my cockpit except I get notifications that two items are running on back up batteries and my com 2 shuts off. No big deal...
 
A Positive Perspective

+1 on Robert's and John's posts.

Dan, you might want to stop this negative "sky is falling" stuff. What you wrote can apply to virtually any aircraft electrical architecture (Bob Nuckolls, EFII, Vertical Power, etc.) in some way. If you want to design the ultimate, automatically fail-safe aircraft electrical schematic or system, please go ahead. Be careful, though. Criticizing is one thing; offering a positive, competitive solution is another.

In many of your past posts on other topics, you have offered positive solutions. How about doing that with respect to aircraft electrical system architectures, particularly in support of redundancy and safety? How about the glass is half full; not half empty? :)
 
For those who don't keep active tabs on the Aeroelectric Connection email list on the Matronics server:
The Bus Manager is definitely NOT in any way remotely similar to what Bob Nuckolls recommends.

I'm not saying it's evil incarnate, or you'll fall out of the sky if it's in your plane. It's just not what Nuckolls has recommended, and that would be clear if you read through the Matronics archives. Everything's a compromise; we each get to pick what we compromise. But we should have our eyes wide open and be fully informed when we pick them.

Almost everyone's happy with a single fuel delivery system; almost everyone's terrified to fly with a single ignition.

There's a simple solution to the questions about the box; just publish here, for peer review, the internal diagram of the box.

Charlie
 
Bus Manager

Hi Charlie,
The current paths drawing is in the installation manual on our Downloads page,
Robert
 
Wonderfull propaganda effort Dan - bravo!
It's going to take awhile for my Internet bologna meter to unstick its needle.

Perhaps you could offer a sincere technical response.

Your words: Most importantly, it provides two separate current paths to the engine electronics that do not require pilot intervention to manage.

Show us the two separate current paths.
 
Almost everyone's happy with a single fuel delivery system; almost everyone's terrified to fly with a single ignition.

Charlie

We will fly with a single ECU, single alternator, single set of spark plugs. We do have dual batteries. No, we are not terrified.
 
At the risk of getting flamed...

If you take the step of installing two batteries, you enable a set of new options for power distribution that significantly enhance redundancy and reliability.

I offer that boxes like this and VPX provide function but may hinder redundancy and reliability objectives.

If anyone is interested in a two battery system that does not require a box, send me a PM with your email address.

Carl
 
Wonderfull propaganda effort Dan - bravo!
It's going to take awhile for my Internet bologna meter to unstick its needle

Perhaps you could offer a sincere technical response.

Separate posts, to keep things clear.

I wrote:

Both pumps are driven by the same single wire, breaker, and relay. A shorted primary pump annunciator circuit, a shorted pump power circuit, or a shorted pump motor will all pop the circuit breaker. Of course the BM will detect the loss of fuel pressure, but the "fully automatic pump management" can't make the second pump run until the pilot diagnoses the cause of his no-run condition, then finds and resets the circuit breaker.

Specifically, what fault do you find in this failure analysis?
 
I am installing the Bus Manager and I did one upgrade. I installed my fuel pumps on two separate circuit breakers and running through two relays. Both relays get their signals from the Bus Manager. My electrical feeds to the fuel pumps are now separate and independent. I do plan to test the system at each start of the aircraft.
 
I am installing the Bus Manager and I did one upgrade. I installed my fuel pumps on two separate circuit breakers and running through two relays. Both relays get their signals from the Bus Manager. My electrical feeds to the fuel pumps are now separate and independent. I do plan to test the system at each start of the aircraft.

I guess the question is, what happens if the signal from the bus manager fails? Do you have an override?
 
I'm flying it...
With 2 alternators and two batteries feeding the buss manager, I've got a fair amount of protection.

Yes, you're flying it.

Are you wired with both EFI and EI systems on the BM's single essential bus output?

Do you run both pumps from the same breaker?

BTW, love is blind.
 
Dan, you might want to stop this negative "sky is falling" stuff.

Bill, why is it negative to discuss claims which appear to be false or misleading? And is it unreasonable to ask a manufacturer to offer serious technical response when those claims are questioned?

In many of your past posts on other topics, you have offered positive solutions. How about doing that with respect to aircraft electrical system architectures, particularly in support of redundancy and safety?

You mean like this one....

http://www.vansairforce.com/community/showpost.php?p=1120754&postcount=39

...or this one....

http://www.vansairforce.com/community/showpost.php?p=1027569&postcount=19

...or this one?

http://www.vansairforce.com/community/showpost.php?p=1028544&postcount=28

There are more. These are serious attempts to think and explain. Not that my contributions amount to a hill of beans compared to simply buying (and studying) a copy of The Aeroelectric Connection. And Marc Ausman's Aircraft Wiring Guide is very good for builders going conventional, or with a VPX.
 
I am installing the Bus Manager and I did one upgrade. I installed my fuel pumps on two separate circuit breakers and running through two relays. Both relays get their signals from the Bus Manager. My electrical feeds to the fuel pumps are now separate and independent. I do plan to test the system at each start of the aircraft.

Paul, all that is based on acceptance of the idea that you can't run two electric pumps in parallel. However, that claim has been questioned by Ross Farnham, who has been working with this specific equipment for a very long time:

http://www.vansairforce.com/community/showpost.php?p=1121221&postcount=49

Consider the KIS principle. It has two basic truths. (1) Components and wiring not installed never fail. (2) Simple and conventional is understood by all users.

Now consider ditching all the wires and relays and connections to a master brain. You already have a brain. Simply wire a primary pump to run with ignition on, and a switched secondary pump switched on for takeoff and landing, just like every other airplane.
 
I guess the question is, what happens if the signal from the bus manager fails? Do you have an override?

The way I look at that is I test the signal wire at every start of the aircraft. If it does not work I do not fly. If the signal wire fails in flight there would also have to be a failure in the fuel pump as well. That requires two independent failures. That is acceptable in my risk tolerance.
 
We will fly with a single ECU, single alternator, single set of spark plugs. We do have dual batteries. No, we are not terrified.

And you're not almost everyone. And it's not a Lyc, or even an a/c engine. Not knocking that; I'm building an alt engine installation, too. But you're making my point; everyone picks the compromises they're comfortable making. If you're fully informed and making intelligent choices, carry on. If you're *not* fully informed and making intelligent choices, then you might be taking unnecessary and unknown risks.

And as Dan just mentioned, love is blind. If we don't get others' experienced and qualified eyes on our decisions, we can be blinded to faults, or even easy improvements, for that matter.

Charlie
 
Paul, all that is based on acceptance of the idea that you can't run two electric pumps in parallel. However, that claim has been questioned by Ross Farnham, who has been working with this specific equipment for a very long time:

http://www.vansairforce.com/community/showpost.php?p=1121221&postcount=49

Consider the KIS principle. It has two basic truths. (1) Components and wiring not installed never fail. (2) Simple and conventional is understood by all users.

Now consider ditching all the wires and relays and connections to a master brain. You already have a brain. Simply wire a primary pump to run with ignition on, and a switched secondary pump switched on for takeoff and landing, just like every other airplane.

Dan,

The suggested wiring of the fuel pumps is certainly a big concern of mine as I consider this system for my -10.
I think I've seen you state elsewhere that you had a concern about overheating the pumps by running them simultaneously due to less fuel flow through each of them. Something to that effect.

I've seen Bob N. endorse doing what you've suggested.
Is running the pumps in parallel less of a concern to you now?
 
Adam,

I'm not Dan, and I must have missed the memo about running 2 pumps in parallel. I don't see the issue, unless the fuel regulator and/or bypass line aren't sized properly.

The automotive injection pumps everyone's using are positive displacement; they pump what they pump, at a given voltage, or if blocked, stall & potentially overheat (if self protection isn't adequate). If the regulator can handle 2X the normal flow, and the bypass line can handle 2X normal flow, the only issue is available electrons.

Thinking further, you do need to consider the supply line, as well. You don't want to suck a vapor bubble in the feed line. But a -6 line will flow an impressive quantity of fuel, if it's kept short & bends are minimized.

Charlie
 
Fuel Pump Mod

I started out having the fuel pumps on separate breakers. For one...
Then, (if you read my detailed write up) you'll see,I added a "BOTH FUEL PUMPS" switch. This enables me to bypass everything and send power straight from my essential buss to both pumps.
 
I think I've seen you state elsewhere that you had a concern about overheating the pumps by running them simultaneously due to less fuel flow through each of them. Something to that effect.
I've seen Bob N. endorse doing what you've suggested.
Is running the pumps in parallel less of a concern to you now?

The prohibition first came to my attention in a presentation by Mr. Paisley. Later I noticed ULPower was also running one at a time for the same stated reason. However, Ross says it's no problem.

Why wonder? Set up a test rig and end all question.
 
I started out having the fuel pumps on separate breakers. For one...
Then, (if you read my detailed write up) you'll see,I added a "BOTH FUEL PUMPS" switch. This enables me to bypass everything and send power straight from my essential buss to both pumps.

I assume "everything" is the BM's pump switching circuitry.

You're running both your EFI/EI systems from the essential bus alone? Pumps too?
 
fuel pump wiring

The Bus Manager fuel pump wiring is very simple and diagrammed in the manual.
It does not require a signal from the Bus Manager to keep a pump on.
There is always one pump running regardless of the state of the signal (or lack thereof) from the Bus Manager. That is part of the beauty of the circuit.
Some people put a breaker on the power to each pump instead of one breaker before the relay - no problem with this.

It is very difficult to have an engine shut off with a Bus Manager protecting the power. Even if the key switch fails, if an internal relay fails, if the normal diode ORing fails - you can still get power (from either battery) to the essential bus with the emergency power switch.

When people try to implement their own protected bus structure, it is either a whole bunch of complication to hook up (=unreliable through complication), or it isn't done correctly. The Bus Manager is a simple to install, VERY effective solution to the problem of managing two batteries and creating a protected bus.

A lot of very experienced engineers have gone over its architecture, including myself. People who are experienced with the product don't even think about whether to put it into their next project. There simply isn't a simpler or more robust solution to this requirement at this time in the marketplace.

We actually stopped the development of the EFII system for about a year to solve this problem. It was evident that without a protected bus architecture, these planes would not be safe with an electronically dependent engine.

We have seen significant evolution in experimental aircraft over the last 20 years. Evolving the electrical system is an important part of this path. This process of evolution will continue indefinitely. Maybe there will be a better solution for power distribution in the future. But we have a good solution for today's demands currently available. 200 airplanes, and 10 years of service without an engine shutting off due to a bus outage is a pretty good track record.

Robert
 
Bus Manager

Hello Dan,

In response to your comments:

1. I don’t think Robert (EFII) is trying to be misleading. He has clearly published his Bus Manager schematics online via his downloads page (link below). Although you, and others, may disagree with his Bus Manager architecture at least he is attempting to provide a turn-key product with the redundancy and assurance necessary to proceed with an “all-electric” aircraft (electronic fuel injection plus electronic ignition). Certainly, the primary goal of the Bus Manager is to keep the electrons automatically flowing to the essential bus (including ignition electronics and fuel pumps), and the Bus Manager does that. The Bus Manager also supports fuel pressure sensing and auto-activation of the backup fuel pump if necessary.

http://www.flyefii.com/media/Bus_Manager_Installation_Instructions.pdf

Comment: I think it is a mistake to view and critique the Bus Manager as an all-encompassing aircraft electrical architecture unto itself. The Bus Manager is best viewed and utilized as a core unit within an individual aircraft’s electrical scheme (based on Bob Nuckolls’ Z-14 architecture in my case). For our aircraft, John and I have made some “comfort” mods external to the Bus Manager, but within our aircraft’s individual electrical architecture. In my case, these mods were reviewed and approved by Robert, and I assume that John probably received the same support as well.

I think Robert may get frustrated with the criticism that any experimental aircraft product vendor and VAF advertiser receives, but Robert is great one-on-one and is very objective about the Bus Manager’s capabilities as well as the technical capabilities of his EFII systems. Robert is first an experienced electrical engineer and electronic fuel systems expert and only secondly a marketer, because he must assume the latter, distasteful role (to an engineer anyway) to stay in business. I don’t think any of Robert’s customers would say that he has misled them or not provided full, complete information and great support.

If I was a betting man, I would say that Robert may elect to incorporate some of his customer’s mods (or maybe even some of your suggestions?!) into the next evolution of the Bus Manager. At least, I think Robert may post some thoughts regarding typical mods or integration issues external to the Bus Manager. Certainly, Robert is vitally interested in all his EFII and Bus Manager customers flying safely and confidently. His reputation and business clearly depend on that.

2. Dan, thanks for the links to the comments you have previously posted. I reviewed your posts when you originally made them, and I think your ideas are good. On the other hand, I think what everyone is looking for is an overall, detailed aircraft system schematic for an “all-electric” aircraft; not just part of the picture (like the Bus Manager or your individual ideas). It is something which I confronted when I laid out my aircraft’s electrical system architecture, but, to be honest, I am guilty in that I have not taken the considerable trouble to publish it (mine’s in pencil!). My mods are mine alone, and I’m not good with criticism; either! Also, the term “failure analysis” is most applicable to the overall architecture, and that is where the individual risk decisions are really made.

I see that Carl Froehlich is offering “a two battery system that does not require a box” so Carl’s architecture is probably a good place for builders to start. Bob Nuckolls’ architectures are great, too. I can almost guarantee at some point that builders will end up with part of their architecture looking something like a Bus Manager which is why I elected to go ahead a purchase the box to save me the trouble of fabricating it myself. In other words, I’m getting lazy and burned-out; I admit it.

Well, anyway, my hope is that cooler heads (including my own hothead) will prevail in this discussion and that this thread will support the all-important search for a CONFIDENT aircraft electrical system architecture in support of these new “all-electric” aircraft enabled by EFII and others.

Best Regards,
 
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Bill - Very good comments. I am extremely comfortable with the EFII Bus Manager system, and it has been installed per the installation manual.

The feature that is most appealing to me is the auto switching of fuel pumps, should the primary pump suffer a failure, or reduced fuel output. And, this is totally programmable as to the parameters of when you want the switching to occur. The BM most likely would recognize the fault, and take corrective action faster than a human would.

Perhaps my background flying heavy jet transports is why this system looks very good to me.

From a customer service standpoint, Robert has been extremely supportive. That is more than I can say for a number of companies that I have dealt with.

And, there has not been failure of the system, plus there are no unhappy customers.
 
And you're not almost everyone. And it's not a Lyc, or even an a/c engine. Not knocking that; I'm building an alt engine installation, too. But you're making my point; everyone picks the compromises they're comfortable making. If you're fully informed and making intelligent choices, carry on. If you're *not* fully informed and making intelligent choices, then you might be taking unnecessary and unknown risks.

And as Dan just mentioned, love is blind. If we don't get others' experienced and qualified eyes on our decisions, we can be blinded to faults, or even easy improvements, for that matter.

Charlie

My level of comfort comes from the experience of other builders, flying with our basic V8 engine, or other very similar engines, using a single ECU and alternator. A number of them do not even have dual batteries.

While it is not a Lycoming, this SBC has thousands of successful hours in airplane installations.

Of course, we only have one propeller, one crankshaft, and one pilot.

Maybe I need to rethink this after all!
 
I think that takes care of it....

Well, gee, if John is going to hold the game show buzzer, we may as well have some educational fun with failure analysis. Gather round, because everyone can participate in this game.

Below we have two examples of electrical architecture. Both are dual battery, single alternator systems, supporting dual ignition and dual fuel injection. The one on the left we'll call Dual Bus. It's just something I drew this afternoon. The one on the right is based on an EFII-brand Bus Manager, per the install manual.

Game%20Show%20Both%20Systems.jpg


Failure analysis means failing each item in turn, determining what will happen as a result, and then determining how the flight will terminate because of it.

We'll start simple, wires only. A wire can only fail two ways, open or shorted to ground. So, (1) pick any one wire, (2) tell us if it went open or shorted, (3) describe what will happen, and (4) its effect on the flight.

I'll start...

Dual Bus diagram, the wire between the alternator and the ANL. When shorted, the ANL blows. Pilot does nothing. The flight continues on battery power, both batteries connected, all avionics and engine systems operational.

Same wire, failed open. No charging. Pilot does nothing. The flight continues on battery power, both batteries connected, all avionics and engine systems operational.

Your turn....

Fault%20List.jpg
 
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Slightly updated Game Show diagrams; added a neglected a diode connection, changed the Bus manager ground to a better representation, and added its enclosure (dashed box).



Continuing wire by wire:

Dual Bus, feed wire between ANL junction and Main Bus. Fails open; Main Bus devices go dark, except for those with their own internal and/or dedicated batteries. Pilot does nothing, all engine functions continue normal.

Dual Bus, same wire, fails to ground. ANL blows, same result as above (now it's an open).

Dual Bus, between Battery Contactor and ANL junction. Fails open, battery charging stops. Main Bus devices run on alternator power. Pilot does nothing, all engine functions continue normal.

Dual Bus, same wire, fails to ground. Battery is shorted, smoke in cockpit, potential fire. Pilot actions required: open Battery Contactor (Master OFF), pull alternator field CB. Battery charging stops, Main Bus devices go dark, except for those with their own internal and/or dedicated batteries. All engine functions continue normal.

Dual Bus, between Master Switch and Battery Contactor. Fails open, Battery Contactor opens, charging stops, Main Bus devices run on alternator power. Pilot does nothing, all engine functions continue normal.

Peer review of the above please. Goal is an accurate result for each failure.
.
 
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Dan,
To make sure I understand your second scenario, when the wire between the battery contractor and the ANL junction shorts to ground, you have lost (smoked) your left battery, the the engine keeps running on the right battery, correct? Right battery protected in this example by the diode between it and the battery contactor. I'm assuming the shorted wire didn't burn in two, and you are therefore also smoking the alternator, hence - trip the field.... Is that right?

It might seem like a good idea to know how long you can run on one battery, however, any time there's smoke in the cockpit and you don't land on the closest suitable runway....... there might be something wrong with you.
 
Dan,

For my installation (not yet flying), instead of ANL's, I just used 8AWG for alternator B lead with a soldered length of 12AWG fuselink wire on the load end to protect the wire. I did the same thing (source end) on the wire that feeds my bus. I picked that option after looking at the available ANL holders, & decided that a soldered/heatshrunk joint at the wire/link joint, and a soldered or crimped (your choice) screw terminal on the link end would be more reliable. Since the link is only there for catastrophic events, I saw more risk in the multiple joints around the ANL, and low probability of ever needing to replace the link.

Question about the alt>main bus path: Is the permanent connection intentional? Though an unlikely failure mode, a failed & partially shorted alternator could draw down battery energy without opening the ANL, if you don't have a way to disconnect the alternator. Is there overvoltage protection implied but not shown in the drawing?

Charlie
 
Dan,
To make sure I understand your second scenario, when the wire between the battery contractor and the ANL junction shorts to ground, you have lost (smoked) your left battery, the the engine keeps running on the right battery, correct? Right battery protected in this example by the diode between it and the battery contactor. I'm assuming the shorted wire didn't burn in two, and you are therefore also smoking the alternator, hence - trip the field.... Is that right?

Good comment. If it is a truly solid short to ground, yes, you're right, in an analysis it's probably best to assume it could take out the main battery before the pilot could open the battery contactor. If it is the "arc and spark" kind of short, not so well connected to ground, the battery would probably survive. Right battery is protected, so at least one EI/EFI remains up regardless.

The alternator may or may not overheat and die, but it doesn't matter. With smoke in the cockpit, I think everyone's trained response is to shut down the electrical system right now...Master OFF, alternator field OFF. It's the standard red split switch in a spam can, or a toggle and a pullable CB in my RV. In this system, doing so has no effect on EI/EFI, just like it has no effect on mags in a spam can. Nor is the pilot expected to turn something ON before he turns something OFF.

That particular wire (or big cable) is pretty much universal in conventional wiring. In a rear battery RV-8, for example, it would be a #2 or #4 cable from behind the rear baggage to the firewall area, most often to a start contactor terminal, where it is tapped for alternator and bus feeds.
 
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The protection for each line should be on the output of the contactor, as shown for the fuselink in the drawing. That should answer Scott's concern.
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BTW, conventional field wound alternators are effectively self-limiting, when it comes to current. A dead short on the output would probably be death for it eventually, but it can't do more than it can do. So if it's a 60A rated alt, it'll probably pump about 65A to ground for quite a while before dying. That's why the B lead should be sized to handle a bit more than full rated alt output, and then protected on the other end (from battery current).
 
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For my installation...

Right now the game is wire failure analysis. You're a smart guy; pick one from either diagram, short it or open it, tell us what happens next, and the effect on the flight.
 
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First spectator dumb enough to say I'm looking forward to learning here and smart enough to not pick a wire to cut open or short here, yet!
 
I'll take a hack at it. Fun challenge.

Please correct me if I miss something or don't get it right - an unfortunately likely possibility.

On the DB, the wire between the master and the battery contacter opens. I think the alternator will keep the main bus up. Otherwise nothing happens.

The same wire shorts to ground. Everything keeps working except that on shut-down, the main bus stays on.

I think the EFI 1 bus in entirely unaffected by either of these events.

On the BM, the wire between the emergency switch and the essential bus opens. There will be no change and the plane keeps flying.

That wire shorts to ground. The essential bus dies and the motor stops. If the emergency switch is then flipped on, both batteries and the alternator are shorted to ground. In spite of the alternator breaker opening, there are sparks and some smoke to enliven the silence.

Dave
 
Buss Manager: Any fault (open or short to ground) between the ESS Bus relay in the box, and the ESS Bus itself, causes engine stoppage.

A fault to ground on that wire at best blows diodes, and depending on whether there's undrawn circuit protection, likely starts something burning.

While unlikely, a fault to ground inside the box after *either* diode pair takes both batteries to ground, until something burns open.

Loss of 'ignition key switch' control line causes loss of both busses; only the 'ESS Bus' is recoverable with the Em Pwr switch.

Not part of the failure analysis, but it's not hard to design around loss of the main bus power feed, if desired. I mention this because while the main bus might not be required to keep flying, it could well contribute to safe(r) conclusion of flight, and some failure scenarios wouldn't *require* shutting it down.

Charlie
 
Buss Manager: Any fault (open or short to ground) between the ESS Bus relay in the box, and the ESS Bus itself, causes engine stoppage.

A fault to ground on that wire at best blows diodes, and depending on whether there's undrawn circuit protection, likely starts something burning.

While unlikely, a fault to ground inside the box after *either* diode pair takes both batteries to ground, until something burns open.

Loss of 'ignition key switch' control line causes loss of both busses; only the 'ESS Bus' is recoverable with the Em Pwr switch.

Not part of the failure analysis, but it's not hard to design around loss of the main bus power feed, if desired. I mention this because while the main bus might not be required to keep flying, it could well contribute to safe(r) conclusion of flight, and some failure scenarios wouldn't *require* shutting it down.

Charlie

What are the odds of the above cited fault occurring? Exactly what would be the most likely cause?
 
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