My wiring diagram with VPX and EFII componets

A thread was started by Scott Balmos earlier to encourage members of this forum to review his electrical diagram for his aircraft. I am at the same point in my build and it inspired me to get my drawings done.

The aircraft will be using the EFII’s fuel injection and dual ignition systems integrated with the VPX system. The review of Scott’s diagram made me think differently of my original designed system. My diagram is at a point that I want to encourage others to review my diagrams and give me feedback.

I have elected to have an electrical dependent aircraft with dual fuel pumps, ignition systems and alternators. I have three busses; main through the VPX, Essential for the engine and a Battery Buss for an alternate power for mission critical components in the event of a VPX failure.

in the event of a software failure, I plan to carry a Stratus and iPad along with a portable radio for additional redundancy.

https://www.dropbox.com/s/huean6xr27g2jjm/N219PB Wiring Rev2.pdf?dl=0

This is my latest drawing

N219PB rev4

What did you use to design your diagram?

AutoCAD.

I converted it to a pdf so that anyone would be able to view. Did it view OK?

1st thing I saw was the fuses on the alternators. Circuit protection on an alternator that's a lower current rating than the alternator's output ability is asking for nuisance trips (blown fuses). Maybe a low probability, but an undercharged battery or other unforeseen high demand situations can max out the demands on an alternator, driving it to full or even above full rated output. Best practice is to size wire for significantly higher current than alt's rating (most can do more than their rating), then fuse to protect the wire.

2nd, what type alternators? If internally regulated (don't see external regulators in drawing), and they aren't diode isolated, they will likely fight each other's regulating ability. Regulators are available that have setpoints far enough apart to avoid this; other options are available if using internally regulated alternators.

3rd, I know nothing about the EFI buss manager, but I see only one Power path feeding the essential buss/engine controller components. Is that correct? If so, it's a single point of failure on 'essential' stuff.

4th, overvoltage protection??

Do you have the Aeroelectric Connection book?

Charlie

rv7charlie said:

1st thing I saw was the fuses on the alternators. Circuit protection on an alternator that's a lower current rating than the alternator's output ability is asking for nuisance trips (blown fuses). Maybe a low probability, but an undercharged battery or other unforeseen high demand situations can max out the demands on an alternator, driving it to full or even above full rated output. Best practice is to size wire for significantly higher current than alt's rating (most can do more than their rating), then fuse to protect the wire.

I am not sure which fuses that you are speaking of. I have a 60 amp shunt for the 60 amp alternator and a 30 amp shunt for the 30 amp alternator. I purchased both of them from B&C with the alternators at the same time. The 5 amp fuses are for the alternator field circuit.

2nd, what type alternators? If internally regulated (don't see external regulators in drawing), and they aren't diode isolated, they will likely fight each other's regulating ability. Regulators are available that have setpoints far enough apart to avoid this; other options are available if using internally regulated alternators.

They are both externally regulated alternators. For this schematic I did not include. I will continue to develop the drawing. They are not isolated. I am choosing to keep them manually activated. I could have purchased the regulators with different voltages so that I could have left both on but decided that I could manage. The reason for having two toggle switches instead of a SPDT is so that when the aircraft is shut down I can run my hand along all switches and they should be down. My plan is to cycle through the alternators curing startup to verify both are operating and run on the 60 amp alternator. If I get a low voltage alarm, 12.5 volts, I will look at the screen, take my time because there is no immediate threat that requires split second decisions, switch off the primary alternator and activate the 30 amp alternator.

3rd, I know nothing about the EFI buss manager, but I see only one Power path feeding the essential buss/engine controller components. Is that correct? If so, it's a single point of failure on 'essential' stuff.

The Bus Manager has a bypass switch internal to it that connects the essential bus to the battery lead coming in to the unit. That is the Emergency Bus switch on the side of the Bus Manager. A neat feature of the Bus Manager.

4th, overvoltage protection??

The external regulators from B&C have the overvoltage built in to them.

Do you have the Aeroelectric Connection book?

Yes, I have Bob's book. A lot of good information. I tried to incorporate his philosophies into my design but some of the new electronic hardware that is available now is not described in his books so you cannot go directly from the book.

Charlie

Click to expand...

Thanks for your review. Please let me know if these responses adequately addresses your comments. They are most appreciated.

Perhaps it would be best if you would verbalize exactly why the system is arranged this way.

What do you wish to achieve, why did you select particular components, and why are they connected as they are?

Dan,

Here are planning thoughts on designing my electrical system. My aircraft?s mission is to fly primarily VFR. I do plan to expand my radius beyond the 300 miles that I normally kept with my Cessna 150. My 150 was IFR certified but I never got my ticket. I should have. With that said, I am not going to install the systems necessary for this aircraft to fly IFR until I know that I will be committed to taking the training. I will leave room in the panel for a certified WAAS GPS.

I decided to incorporate electronic fuel injection for ease of engine starting and operation (no mixture control). If I realize some fuel savings, so be it. My goal is not to squeeze every last horsepower out of the engine. The Lycoming 360 will make slightly over 180 hp. Electronic ignition is another good technology that I also want to embrace. I have had a few instances of Slick mag problems in the past. They were not dramatic events, just cost me money. Both of these technologies will make the engine easier to operate and run smoother in my opinion.

For my fuel injection and ignition systems I have decided to go with the EFII?s components. There are many different systems to choose from and there are plusses and minuses to all of them. With that said, my aircraft will be electrically dependent.

I am choosing the EFII?s Bus Manager for its capability to switch on the main and essential bus and switch the fuel pumps if the fuel rail pressure degrades. I believe that the electronic relays are more reliable that traditional master solenoids. The capability of the Bus Manager to switch the fuel pumps is a good capability as I would have to install additional components to perform this function. I do not want to have to have a pilot?s intervention necessary for this function. It needs to happen instantaneously. The system will give me an alarm stating that the switch has been made.

The Bus Manager has two internal busses. The essential bus is dedicated to run the engine components. It has an internal bypass switch in the event that its electronic relay fails. The main bus feeds all of the other components through the VPX system.

I have chosen the VPX system for its electronic circuit breakers and simplicity of installation. It also has many other features that integrate flap control, wig wag of the lights, etc.

In the event of a VPX failure I have identified components that I feel are necessary for flight. The Battery Bus Bar provides an alternate power source for these components. I am planning my panel so that these emergency backup switches and the switches necessary to start the aircraft are going to be in the upper left hand corner of the panel. The switches that are associated with the VPX will be along the bottom of the panel and will be used during flight operations.

I have elected to install a backup alternator in lieu of a backup battery. I know that I could do both but I have not heard of a battery failure in flight that caused an aircraft to go down. A battery failure typically will not allow the engine to start and that is a problem on the ground. An alternator failure in flight will give me a low voltage alarm, not an immediate emergency. I will be able to switch off the primary and activate the backup. I could put in an alarm that would sound if both field wires are on at the same time or install regulators with different voltage set points. My thought process at this time is to keep the alternator selection simple and manual.

Again, thanks for your review.

The dropbox diagram shows 40A & 30A fuses on the two alternator outputs.

If you're using B&C alternators/regulators, you have the option to use their 'backup' regulator, which allows both alternators to be on line at the same time, ensuring that if one drops out, the other is already active (and you get notification if you lose one). That way, the alternator field controls can be simple circuit breakers that are left on all the time during normal operations, just like a car. Advantage: lower workload for crew. Personal preference, but I actually like the fact that I can ignore the electrical system in my car unless there's an actual problem.

If I'm reading the diagram correctly, it looks like there's a lot of extra switching to supply alternate feeds to non-essential stuff like radios, landing lights, etc from two sources (VPX Sport or Battery Bus), but no truly independent alternate feed to the essential (engine) bus.

Again, I know nothing about the EFII Bus Manager...But I see only one power path from the alternators/battery through the bus manager to the engine DC power bus. Does the 'Emerg Pwr Ess Bus' switch actually tie the B+ from the manager power input directly to essential bus bar (meaning that it's a >20A switch), or is it a low current switch that controls a relay inside the manager? If the latter, then the bus manager is still a single point of failure. A workaround would be a high current switch that can tie the battery bus & essential bus together, giving an alternate DC path to the essential bus.

I'm setting up an electrically dependent engine, too, and I'm looking at ways to get the two alternator feeds into the engine bus on separate wires, so a single failure (wires & especially, crimped terminals can fail) won't take out the engine.

Hoping the above is helpful, and not just picking nits....

Charlie

rv7charlie said:

The dropbox diagram shows 40A & 30A fuses on the two alternator outputs.

I must have uploaded an earlier version of my file. I corrected that to show 60A and 30A for the primary and backup. I will update the file tonight. My bad.

If you're using B&C alternators/regulators, you have the option to use their 'backup' regulator, which allows both alternators to be on line at the same time, ensuring that if one drops out, the other is already active (and you get notification if you lose one). That way, the alternator field controls can be simple circuit breakers that are left on all the time during normal operations, just like a car. Advantage: lower workload for crew. Personal preference, but I actually like the fact that I can ignore the electrical system in my car unless there's an actual problem.

I spoke to B&C about this and you are correct, this would make it just like a car. My current understanding of that system is that it is totally automatic and I would not be able to cycle the alternators manually. My plan is to cycle each alternator right after starting the engine and verifying oil pressure. That way I will know at the start of each flight both alternators are functional.

If I'm reading the diagram correctly, it looks like there's a lot of extra switching to supply alternate feeds to non-essential stuff like radios, landing lights, etc from two sources (VPX Sport or Battery Bus), but no truly independent alternate feed to the essential (engine) bus.

Again, I know nothing about the EFII Bus Manager...But I see only one power path from the alternators/battery through the bus manager to the engine DC power bus. Does the 'Emerg Pwr Ess Bus' switch actually tie the B+ from the manager power input directly to essential bus bar (meaning that it's a >20A switch), or is it a low current switch that controls a relay inside the manager? If the latter, then the bus manager is still a single point of failure. A workaround would be a high current switch that can tie the battery bus & essential bus together, giving an alternate DC path to the essential bus.

The Emerg Pwr Bus switch is a >30A rated switch that carries the full load of the essential bus. It ties the batt 1 connection directly to essential bus connection on the Bus Manager. It basically bypasses the Bus Manager.

I'm setting up an electrically dependent engine, too, and I'm looking at ways to get the two alternator feeds into the engine bus on separate wires, so a single failure (wires & especially, crimped terminals can fail) won't take out the engine.

Hoping the above is helpful, and not just picking nits....

Charlie

Click to expand...

You are not nit picking. It is the back and forth comments that enable clear communication.

The low voltage monitors from B&C should let you know if either alternator is off line, but you could also still control the alternators manually with 'pull-able' field circuit breakers or better, CB switches.

If the bus manager dies, what's the alternate DC feed to the fuel pump(s)?

rv7charlie said:

The low voltage monitors from B&C should let you know if either alternator is off line, but you could also still control the alternators manually with 'pull-able' field circuit breakers or better, CB switches.

I looked into both of these options. The manufacture of the circuit breakers do not recommend pulling these as a routine occurrence. They did say pulling them will disconnect the circuit but they strongly stated that they should not be used for this purpose. I spoke with B&C about the circuit breaker switches and they told me that they were prone to failure. I do not have any personal experience with them but I have heard that from several sources.

If the bus manager dies, what's the alternate DC feed to the fuel pump(s)?

Click to expand...

The Emerg Pwr Bus is my alternate feed. It jumpers the in and the out of the Bus Manager. It connects the battery to the essential bus. This switch is rated to carry the full 30 amps.

Minor point, but if another pilot wants to fly the plane, they'll need sufficient systems information to manage potential failures successfully. That suggests a section in the POH and thoughtful panel labels.

If they have to figure out an off-nominal switchology at the moment, make it easy for them.

This also applies to maintenance - years from now all this won't be as fresh in your mind as it is now. Leave some breadcrumbs so that you can follow them back.

Dave

David,

You are most correct. I plan to develop a detailed POH with emergency procedures and I am going to have every wire in the plane on my electrical drawings. This is the reason that I like this vetting process. I am open to looking a other ideas.

Paul

219PB said:

I am open to looking a other ideas.

Click to expand...

Paul, have you considered other electrical system architecture? It appears this architecture was driven by a desire to use specific components, rather than a desire to meet certain needs.

Here's an exercise you may find worthwhile. Clean-sheet a few alternate schematics with an eye toward simplicity. The mission is VFR; leave out avionics and accessories for now, as they are not needed to remain above the rocks. What is the least possible system necessary to keep the engine running under all circumstances?

Along those same lines, here's something I learned over many years. We all know what KISS means - it means Keep It Simple, Stupid. What I learned was that not only does it usually lead to both reliability and a reduction in hazard potential, it's elegant in its own right.

KISS isn't easy, though.

Perhaps, as part of DanH's exercises, swap out the electric ignition for a version that doesn't need ship's power. How does that affect the architecture?

Dave
VFR RV-3B

Thanks to everyone for the comments that were given to me. The VPX features are desirable and incorporating them into my design is to my advantage. I also wish to have a traditional engine (Lycoming) that has the ease of operation of a modern automobile engine. Fuel injection will give me many opportunities to utilize avgas, mogas and any new fuel blends that will be mandated by the government in the future.

With that said I looked at my layout and simplified it. I kept the items on the VPX that needed to be there to take advantage of their features while putting components that I deemed necessary for my flight mission. My aircraft will be VFR but I am concerned about VFR night flights and I put the com, ADSB, pitot heat and autopilot on the essential bus. My current draw is just under the 30A limit. I did have to leave the backup power switch for the landing light. I need to leave the primary power for the landing light so that the VPX can perform the wig/wag.

The layout is cleaner and more traditional. I know that did not completely start from a clean sheet but I feel that this design addresses many good points that were brought up. Thanks again for your review.

https://www.dropbox.com/s/qr5a6oouljyqghu/N219PB Wiring Rev1.pdf?dl=0

Paul, you need not justify your desire to have EFI, EI, or to use a VPX. Each has its own advantages and disadvantages, but here in this discussion they are merely systems requiring power; the discussion is about a reliable electrical system.

Let's look at a few things, one at a time.

First, the Bus Manager is designed to be used with two batteries. The primary reason is brownout of the ECU(s) while cranking; the high current demand of a permanent magnet starter pulls bus voltage very low. Two batteries allow cranking with one isolated battery powering the ECU, coils, and pumps, while the other drives the starter.

Per the manual, the Bus Manager can be configured for single or dual alternators, the difference being the addition of an internal diode for battery isolation in the single alternator version. In a dual alternator version, the alternators are isolated from each other, charging the two batteries independently. No special regulator set points are required, nor is there a need for special switching at runup; a standard "alternator out" light will tell you if an alternator isn't charging. Your EIS probably monitors voltage also; just set it to trip an alarm about 12.5V.

Your bio says you are a Reliability Engineer. Can you make a case that the reliability of an alternator (with its support wiring, brushes, regulator, windings, connectors, diodes, and bearings) is superior to the reliability of a chemical battery?

DanH said:

Paul, you need not justify your desire to have EFI, EI, or to use a VPX. Each has its own advantages and disadvantages, but here in this discussion they are merely systems requiring power; the discussion is about a reliable electrical system.

Let's look at a few things, one at a time.

First, the Bus Manager is designed to be used with two batteries. The primary reason is brownout of the ECU(s) while cranking; the high current demand of a permanent magnet starter pulls bus voltage very low. Two batteries allow cranking with one isolated battery powering the ECU, coils, and pumps, while the other drives the starter.

You are correct about the permanent magnet starter. I chose a series wound from B&C that will draw much less current, ~250A according to B&C. The ECU will operate down to 7 volts. I am not as concerned about this issue.

Per the manual, the Bus Manager can be configured for single or dual alternators, the difference being the addition of an internal diode for battery isolation in the single alternator version. In a dual alternator version, the alternators are isolated from each other, charging the two batteries independently. No special regulator set points are required, nor is there a need for special switching at runup; a standard "alternator out" light will tell you if an alternator isn't charging. Your EIS probably monitors voltage also; just set it to trip an alarm about 12.5V.

I like the Bus Manager, but with their two alternator setup the backup alternator just feeds the second battery and essential bus. In the event of a primary alternator failure, I will lose the charging capability for the main bus. This would not be the end of the world, but if the system is configured so that either alternator can feed the whole system, I would just have to manage the load, i.e. cut off seat heaters, extra lighting, defrost fan, etc to accommodate the reduced capacity of the second alternator.

I am thinking however, if the second battery is installed the primary alternator fails, the main buss would be running off of the main battery. These low loads would allow me to select the best alternate airport and not necessarily just the ones within gliding distance. Operating with the alternators configured to each battery would also allow me to continuously monitor the health of both alternators.

Your bio says you are a Reliability Engineer. Can you make a case that the reliability of an alternator (with its support wiring, brushes, regulator, windings, connectors, diodes, and bearings) is superior to the reliability of a chemical battery?

I hear you on the reliability issues but I have had a few personal experiences where a battery lost a cell and I was not aware until I started the engine on the next flight. I wish there was a battery capacity meter but there isn?t one. An alternator is a constant source of power, i.e. second battery, and its capacity is known from one second to the next.

Click to expand...

I will admit that this conversation has gotten me thinking more about my setup. The way that I have my alternators currently configured would have the backup alternator in the off position during the flight and it will be a hidden failure. This means that I will not know its condition until I energize it. That was the reason I wanted it to be part of my startup routine so I could verify its operation.

I am going to reconfigure my system to have the second battery. As I was writing this reply my perspective was being modified. I left all of the responses above to document my initial reasoning. Hopefully this will be a help for others. Give me a couple of days and I will have the drawing updated. Thanks for the challenge process.

Ok, let's next look at fundamental need, and design from there. I previously suggested considering other architecture by starting with the most basic possible systems. The following drawings are conceptual, not schematics.

This is the least possible system necessary to keep the engine running under all circumstances:



It is two entirely isolated systems. A failure in one system has no effect on the other, and no significant effect on engine operation. Nothing we add from here should be allowed to change those two parameters.

The batteries are electrical storage tanks. They should have enough capacity to maintain engine operation beyond exhaustion of the petrochemical energy in the other storage tanks. Note that doing so does not require running both sets of ECUs and ignitions at the same time. For example, if you have four hours of fuel, each battery might offer three hours of engine operation, minimum.

For normal operation we must constantly refill those batteries, so we add alternators. We also have other things we would like to power, so we'll add busses:



Note the busses are separate from engine power supply. We want to be able to isolate them (turn them off) without affecting the engine power supply. It's a very good functional design what-if; can the pilot make the airplane totally dark, and still fly until fuel exhaustion?

A VFR airplane does not require backup power for an autopilot, a com radio, or a landing light. Those things are nice to have, but if they are essential to a VFR flight, what we really have is a pilot problem. We can place them on an ordinary main bus or VPX, and use them or not, depending on conditions and flight time required to get safely on the ground. The battery and alternator used on that side of the system are sized for loads and duration in the usual fashion.

The other battery and alternator is for engine system power only. They too are sized for duration, but have no other loads. The alternator can be quite small, as can the battery:



Let's flesh out the conceptual architecture just a little by thinking about connecting devices. Nothing real fancy is required. In fact, the least fancy is desired, as it is almost always more reliable than the complicated system, both in physical mechanics and in human factors...the KISS principle at work. Even a dual bus system can be simple.

Dan,

Thanks for your comments. I agree about the AutoPilot. I only included it on the essential bus because I do plan to fly night VFR and in the event that I get into some weather it could reduce the pilot work load if necessary. I never had an AutoPilot before so that will be new to me. The other reason is am leaving panel space so that I can upgrade the aircraft with IFR equipment at some date in the future.

A question. What is the ANL box and the CONT box on your diagram?

I have updated my drawing again and have attached it. There are details around the starter select switch and the start button from the Bus Manager and the VPX that I still need to work out. I am going to get the signal from the VPX because it will has the starter disable to keep the starter from engaging while the engine is running. I know I can wire it up but I just need to determine the cleanest way to accomplish this.

https://www.dropbox.com/s/huean6xr27g2jjm/N219PB Wiring Rev2.pdf?dl=0

A question. What is the ANL box and the CONT box on your diagram?

Click to expand...

"ANL" designates a particular type of robust current limiter...a big fuse. You would use them in the 30 and 60 amp fuse locations on the alternator b-leads.

Here are a few words from Bob:

http://www.aeroelectric.com/articles/anl/anlvsjjs.html

"CONT" is just my abbreviation for contactor.

I have updated my drawing again and have attached it.

Click to expand...

How do you feel about dual alternators, and dual batteries, feeding dual ECUs, dual fuel pumps, and dual ignitions through a single device to a single bus on a single wire? The Bus Manager architecture appears to be a legacy product from Mr. Paisley's Subaru days, i.e. a single ignition, single ECU engine.

Bus Manager

There is nothing "legacy" about the Bus Manager. It was developed in conjunction with the Lycoming EFII system. It is a complete power distribution and power protection system in one box. The essential bus is a very important component of a modern aircraft electrical system.

Evolution of the airframe electrical system was a very important companion step in opening the door to electronically controlled aircraft engines.
People who are familiar with the EFII system and the Bus Manager, install the the two as a pair and you gain a protected electrical bus as well as the redundancy of the EFII system. It is a very solid topology.
Most people use two batteries and one alternator. If you plan on spending a lot of time over wilderness, or water, or in IFR conditions, a second alternator
can be added.

Our safety and reliability record speaks for itself.

Robert Paisley
EFII

Dan,

The way that I see the Bus Manger is basically two single line busses in parallel that have the added advantage of the primary alternator being able to feed the essential bus if the backup alternator fails. I see the architecture similar to what you have drawn. There is also the added built in benefits of utilizing both batteries for starting if necessary and the fuel pump switching.

What is your opinion on how I have the fuel pumps powered with the alternate legs of the relays?

Thanks for all of your feedback.

Hi Paul,

Part of my problem in giving sensible help is that reading your schematic, it isn't (or maybe it is) like what's shown as the actual bus manager product on the EFII website. I wrote all the stuff below before I went to the site & discovered that the manager and essential bus are apparently the same device, and the main bus portion of the manager isn't shown on your schematic. Having said that....If you're confident that bus manager actually provides redundant paths to the critical components, then never mind.

Charlie

I think that Dan (and I) is/are trying to get you to look at failure points, instead of 'neat' features.

If you read through the Aeroelectric book, Bob's philosophy is that in general, it doesn't matter how reliable something is. He wants an easy 'plan B' to work around any failure that can interfere with safe completion of a flight. Any point(s) in the power path where a break can shut you down with no plan B, is cause for concern.

No doubt the bus manager is a slick product, but according to your schematic, there are 3 obvious things that can stop your engine, with no way to get it going again: 1, the pwr output terminal on the bus manager; 2, the wire from the bus manager to the essential bus, and 3, the power terminal feeding the essential bus. There are quite likely several more inside the bus manager, but we can't see inside it. Any of the 3 listed will stop the engine (and everything else on the bus), with no chance of restarting.

What Dan's concept does, and Nuckols' drawings do, is provide a complete alternate source of power to keep the engine running. I think that Dan would agree that his concept is not the only way to accomplish that goal, but it's certainly a good one. Another method, if you want to keep a single essential bus, is to feed it from 2 separate sources. That's why the Nuckols/B&C 'backup' regulator setup is so attractive; the backup charging system can feed the bus with a completely separate wire.

IIRC, Nuckols even makes the case that if you have 2 independent charging systems that can each run the a/c at least to fuel exhaustion, then none of the buses need to be 'essential' anymore.

Everyone makes good comments. I will look at locating my "emergency power essential bus" switch outside of the Bus Manager. I will put the switch directly from the output of the battery 2 to her input of battery 2. It will take me a couple of days to update my drawing.

rcpaisley said:

There is nothing "legacy" about the Bus Manager. It was developed in conjunction with the Lycoming EFII system.

Click to expand...

Interesting claim. Single ignition/ECU power, sourced from a switched bus, with no battery contactor; sure looks like Subaru architecture. If it looks like a duck and quacks like a duck...aww heck, never mind, read the record. The Egg Subaru customers were installing Bus Managers early on...

http://www.vansairforce.com/community/showpost.php?p=519907&postcount=4

....while Protek didn't even offer dual ECU systems until sometime in 2012, and apparently didn't think they were necessary even then:

http://www.vansairforce.com/community/showpost.php?p=702528&postcount=10

Evolution of the airframe electrical system was a very important companion step in opening the door to electronically controlled aircraft engines.

Click to expand...

Couldn't agree more. Tell us what specific evolutionary changes were implemented at Protek.

Bob Nuckols published drawings Z-1 through Z-22 way back in November of 2001. They illustrate, for example, a diode-fed essential bus with a switched battery feed for for those times requiring main bus shutdown. They also illustrate always-hot battery buses for engine ignitions and fuel pumps.

Of course, Bob didn't try to run 30 amps through diodes, as that would require fans and big heat sinks, and anyway, running the IGN/ECU power through diodes loses some emergency flight duration due to the diode voltage drop.

That does leave the automatic pump switching, an interesting subject in itself.

Bus Manager

Yes, you are correct, there are many types of engines and installations which run our Bus Manager. It is a very robust device with a perfect safety record.
Thank you for pointing that out,
Robert

219PB said:

Dan, The way that I see the Bus Manger is basically two single line busses in parallel that have the added advantage of the primary alternator being able to feed the essential bus if the backup alternator fails. I see the architecture similar to what you have drawn.

Click to expand...

Paul, they're actually quite different. As before, conceptual:



Again, with the EFii Bus Manager, everything hangs on one wire.

Note that two independent systems with ECU/IGN/pump battery feeds don't need an essential bus. You can use or shut down any accessory or bus, and the engine still runs. You can hang an essential bus from either or both independent systems, but it's more workload convenience than essential, violates the KISS principle, and adds failure modes.

As you've already realized, the Bus Manager's "Essential Bus Switch" doesn't actually bypass anything but one relay. It does not bypass the diode array, which apparently runs hot enough to make a heat sink and fan desirable....wasted power.

Re your wiring diagram...pop quiz: Your just cranked the engine, and the hung starter warning light is on. What are you going to do about it?

There is also the added built in benefits of utilizing both batteries for starting if necessary and the fuel pump switching.

Click to expand...

No need to couple both batteries together for start unless they are in a low charge state, in which case you don't want to fly an electrically dependent airplane anyway. The no-start issue is electronics brownout, and even paired batteries may not maintain enough voltage at each compression stroke if charge state is low. The KISS approach is to crank with one battery while maintaining full voltage to the electronics with a separate battery. Nothing new; it's how we already handle EFIS brownout.

What is your opinion on how I have the fuel pumps powered with the alternate legs of the relays?

Click to expand...

Separate NC and NO? Should work fine I guess, assuming you're willing to accept the detonation risk with auto pump switching.

I have made a big change in my electrical schematics. I really like what the VPX can do. I like the state of the art functionality and all of the extra things that it will do (wig-wag, control flap speed, lock out flap extension above the 100 knot speed, etc). My problem is I spoke with VPX directly and they recommended not running critical engine components through the VPX. I also want to eventually use this aircraft for light IFR flights. By the time that I removed the critical engine components from VPX and put all of the backup power switches in the system it started to get real messy and the complexity was getting up there.

I have now removed VPX from my architecture and have designed in other wig-wag and flap speed controllers and I believe that my system is simpler. Not as simple as just running the VPX all by itself. That is very clean. But I feel that my system is more robust.

I am still using the Bus Manager. I have got about 29 amps running through the Essential Bus. The Bus Manager has a switch that basically bypasses the Bus Manager and wires the battery straight to the Essential Bus. I am going to go one step further. I am not going to use that feature, I am going to install the bypass switch external from the Bus Manager. One side of the wire is going to land directly on the battery terminal, go through a switch, and directly to the Essential Bus. I still need to draw in a circuit breaker for this circuit.

I also included a couple of my systems drawings. The main drawing, N219PB rev4, is an overview of the main architecture and the others are function specific so that I can keep it organized. Doing it this way keeps the drawing from being too cluttered.

N219PB rev4
N219PB Elevator Trim
N219PB Flaps
N219PB SV-ADSB-470
N219PB SV-XPNDR-261

Some of these drawings are still being worked on but the intent is there.

Dan,

I have finally gotten back to the electrical part of the build. Took me awhile to decide. I felt that I owed you a response seeing the time that you spent on the reply. I do appreciate it.

I have not discovered the knack for the multiple quotes so bear with me. Your comments are in green.

Note that two independent systems with ECU/IGN/pump battery feeds don't need an essential bus. You can use or shut down any accessory or bus, and the engine still runs. You can hang an essential bus from either or both independent systems, but it's more workload convenience than essential, violates the KISS principle, and adds failure modes.

What I like about the Bus Manager is that it automates certain aspects. If either alternator fails then the other will be able to feed power. I do like the ability for the fuel pump to automatically switch. One less thing to have to do in an emergency. It gets tested at every engine start.

As you've already realized, the Bus Manager's "Essential Bus Switch" doesn't actually bypass anything but one relay. It does not bypass the diode array, which apparently runs hot enough to make a heat sink and fan desirable....wasted power.

I agree on the bypass switch. I installed in my electrical diagram to go straight from the battery to the essential bus. I do need to draw in a circuit breaker. As to the wasted power, I believe that the only time that heat will be generated is when there is a voltage differential across the diodes. In that case I will be glad to accept that because one of the alternators will have failed. This will enable all devices to be able to be powered in this event. With two totally independent busses I would loose one as the battery drained down.

Re your wiring diagram...pop quiz: Your just cranked the engine, and the hung starter warning light is on. What are you going to do about it?


Turn off the key switch

No need to couple both batteries together for start unless they are in a low charge state, in which case you don't want to fly an electrically dependent airplane anyway. The no-start issue is electronics brownout, and even paired batteries may not maintain enough voltage at each compression stroke if charge state is low. The KISS approach is to crank with one battery while maintaining full voltage to the electronics with a separate battery. Nothing new; it's how we already handle EFIS brownout.


Seeing that there will be two batteries, they will not be massive ones. Depending on how my weight and balance works out I may install EarthX batteries. I have a friend that installed a dual set and the engine cranks better with both batteries. I agree that if one does it well that will be the standard operating procedure. I would not used both because by batteries were weak. Cranking with both batteries would put less stress on them.


Separate NC and NO? Should work fine I guess, assuming you're willing to accept the detonation risk with auto pump switching.

I assume by detonation that you are referring to inside the engine cylinders? I do not see what would be the difference if I started the auxiliary pump manually. The engine would still be windmilling. Most likely the fuel rail will still have pressure and the automatic system would catch it and I might not even notice if not for the warning that would come up on my EFIS.

Dan, thanks again for the comments. You got me thinking. Emails don't express the proper tones in a voice.

Paul