Power system architecture for EFI

[RandyAB]

Originally Posted by KatanaPilot

Exactly what I'm doing on my SDS equipped RV-10. Dual bus, dual alternator, dual battery. Yes, there is a cross-tie relay, but it will only be used for start. One bus is dedicated to a single ECU, fuel pump and ignition.

Maybe a bit overkill and obviously adds weight, but for my first electrically dependent airplane, I'm trying to be conservative (at least as far as ensuring electron flow is concerned). I know some will say conservative means magnetos and mechanical fuel injection.

So for those who are running their system off of split, independently powered busses, what do you plan for the fuel pumps and the injectors? Do you keep each bus running one fuel pump (ie: both pumps on all of the time)? How about the injectors? If one bus goes down then you lose half of your injectors. How will the engine run in that situation?

[KatanaPilot]

Yes, in my case each fuel pump will be powered by its respective hot battery bus, circuit breaker protected and controlled by a Milspec Honeywell locking toggle. I would anticipate both pumps on during critical phases of flight and one off the rest of the time. Probably alternate even/odd by calendar day.

The injector power is another issue. Since normally half the injectors (on a 6 cylinder) are controlled (but not powered) by one ECU, each bank of three would be powered its respective bus. If an ECU fails, there is a switch to place all injectors on one ECU. You could switch injector power to that one bus at the same time or you could have a diode protected “injector bus” fed simultaneously from both aircraft busses.

There are concerns using either approach and we are working our way through that to arrive at an acceptable solution.

[rocketman1988]

If you are using the EFII system, you may want to do a bit of research...the stated ECU logic and fuel pump logic may not be what you think...

[RandyAB]

Originally Posted by rocketman1988

If you are using the EFII system, you may want to do a bit of research...the stated ECU logic and fuel pump logic may not be what you think...

I?m using SDS. I?m interested in what you mean by ?not what you think? though.

[rocketman1988]

Originally Posted by RandyAB

I’m using SDS. I’m interested in what you mean by “not what you think” though.

A previous post suggested running both fuel pumps at once from separate busses. The EFII pumps are in a manifold and the mfg does not recommend trying to run two pumps at once.

The injectors on the EFII are controlled by one ECU. You can switch between ECU injector control.

[KatanaPilot]

Originally Posted by rocketman1988

A previous post suggested running both fuel pumps at once from separate busses. The EFII pumps are in a manifold and the mfg does not recommend trying to run two pumps at once.

The injectors on the EFII are controlled by one ECU. You can switch between ECU injector control.

Hopefully Ross or Barry from SDS will weigh in shortly and correct my post below -

Unless I was misinformed, the recommendation from SDS is to run both pumps during critical phases of flight. Similar to turning on your electric pump on an airplane equipped with a mechanical pump - you want a backup in case one or the other pump fails.

On SDS one ECU controls half of the 6 injectors and the other ECU controls the other half. There is a switch to flip if one ECU fails so the working ECU controls all injectors - but you lose some functions.

EFII System 32 may be different.

[rocketman1988]

Yes, likely some differences...wasn't sure which you were using.

[RandyAB]

Originally Posted by KatanaPilot

Yes, in my case each fuel pump will be powered by its respective hot battery bus, circuit breaker protected and controlled by a Milspec Honeywell locking toggle. I would anticipate both pumps on during critical phases of flight and one off the rest of the time. Probably alternate even/odd by calendar day.

The injector power is another issue. Since normally half the injectors (on a 6 cylinder) are controlled (but not powered) by one ECU, each bank of three would be powered its respective bus. If an ECU fails, there is a switch to place all injectors on one ECU. You could switch injector power to that one bus at the same time or you could have a diode protected “injector bus” fed simultaneously from both aircraft busses.

There are concerns using either approach and we are working our way through that to arrive at an acceptable solution.

Krea I would be interested in seeing the solution you come up with for the injectors in particular. I had difficulty resolving that problem without introducing a level of complexity that made the overall system more complex and less reliable. For me at least there was no free lunch. The way I set up mine the only real danger is the unlikely event of shorting the entire to bus to ground, a risk that easily can be mitigated.

[tims88]

Originally Posted by KatanaPilot

On SDS one ECU controls half of the 6 injectors and the other ECU controls the other half. There is a switch to flip if one ECU fails so the working ECU controls all injectors - but you lose some functions.

I think you've got the injectors mixed up with the spark plugs. My understanding from the installation manual is that the injectors are all controlled by only one ECU at a time, but each ECU only controls half of the spark plugs.

From the SDS installation manual:

Fuel ECU Switch
When running dual ECU boards, this toggle switch activates relays which switch operation of the
injectors from one ECU board to the other. In normal operation, one board is always firing the top
spark plugs, the other fires the bottom plugs. The ECU select switch only switches the injector
connection over to the other board. If one ECU board fails, you?ll lose one set of plugs but the engine
should continue to run.

[KatanaPilot]

Originally Posted by tims88

I think you've got the injectors mixed up with the spark plugs. My understanding from the installation manual is that the injectors are all controlled by only one ECU at a time, but each ECU only controls half of the spark plugs.

From the SDS installation manual:

From the 6 cylinder dual ECU supplement -

?In NORMAL position both ECU?s will operate and each ECU will control 3 injectors.?