Power system architecture for EFI

[tims88]

Originally Posted by KatanaPilot

From the 6 cylinder dual ECU supplement

Ah, I forgot about that one.

[rv6ejguy]

As far as running the pumps, we say it's personal preference. I only use one at a time- pump 1 on odd days, pump 2 on even days. Verify operation of each during startup or runup before each flight. Make this a checklist item.

Some folks like to have both on for takeoff and operation below 1000 feet AGL.

I've stated in the past that running both pumps will increase fuel pressure a few psi which will cause the engine to run slightly richer. Normally this presents no issues if the system is properly mapped.

I'd certainly just run one pump in cruise. No reason to be pumping a ton more fuel around in a circle and putting more hours on the pumps. Current draw is obviously doubled with 2 pumps on as well.

[KatanaPilot]

Originally Posted by RandyAB

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.

I was originally leaning towards a switch to transfer power for the injectors, but now I'm seriously considering the approach that AdamB has suggested - a small "injector bus" fed by both aircraft busses through Schottky diodes. As you stated, there is no free lunch and of the options, the diode protected bus requires no pilot intervention (except in the case of SDS to flip the injector relay switch). As you stated, it should be relatively easy to design and install a well protected bus.

I have not come up with a simple, reliable design to completely isolate both power sources to run fully independent channels of ECU, fuel pump, coil packs AND injectors given the design of SDS. Maybe EM-6 will provide some improvements in this area.

[RandyAB]

Originally Posted by KatanaPilot

.....a small "injector bus" fed by both aircraft busses through Schottky diodes.......

I may be misunderstanding and I thought of this as well but if either bus shorted it would still take out the injector bus. If that is the case, haven?t accomplished anything other than doubling the risk of taking the whole bus down and added extra weight, complexity, and cost. That?s how I?m reading it.

[KatanaPilot]

Originally Posted by RandyAB

I may be misunderstanding and I thought of this as well but if either bus shorted it would still take out the injector bus. If that is the case, haven’t accomplished anything other than doubling the risk of taking the whole bus down and added extra weight, complexity, and cost. That’s how I’m reading it.

Maybe one of the experts will weigh in and provide a better answer/solution.

I'm sure there are other possibilities, but it seems the choices are -

1. Run all injector power through a double pole, three position switch - requires pilot intervention in the event of ECU failure.
2. Diode protected injector bus. Multiple ways of feeding it, no intervention required.
3. Relay arrangement similar to the SDS injector relay box - but carries power to injectors vs. grounds for injectors from ECU's. Somewhat complex and requires pilot intervention.
4. Ditch SDS and go back to magnetos or pMags, Lightspeed, CPI-2 and mechanical FI.

None of the solutions are perfect. As to added weight and cost for the diode bus - a couple of diodes and a few extra wires really don't weigh or cost enough to matter. Doesn't seem to be too difficult to minimize the possibility of bus shorting.

What is your preferred solution?

[rocketman1988]

A diode bus is basically what the EFII Bus manager does...

See drawing 5 and 5A...

https://www.flyefii.com/media/Bus-Ma...ons-1-6-20.pdf

[RandyAB]

Originally Posted by KatanaPilot

What is your preferred solution?

My solution is essentially what Ross put out.

I have two batteries, each directly feeding one bus via diode feed. Each of the direct feeds will be protected by a slow blow fuse and wire sizes to handle everything on the bus. Each component will be protected by either a fuse (injectors) or c/b?s (coils, ECU?s , relays) Both batteries are isolated from each other by a x-tie contactor, and each system has an alternator. With this system, the only real danger is for the whole bus to short to ground which can be mitigated with proper installation techniques. If one battery were to fail, the other would power the bus with no intervention required. I can kill all power to the other systems in the event of smoke except the engine bus and it will keep the fan turning. PM if you want to see the schematic.

[johnbright]

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...

Also note coil configuration is different for six-cylinder engines SDS versus EFII. SDS uses two six-cylinder coils whereas EFII uses three four-cylinder coils.

[KatanaPilot]

Originally Posted by johnbright

Also note coil configuration is different for six-cylinder engines SDS versus EFII. SDS uses two six-cylinder coils whereas EFII uses three four-cylinder coils.

The two 6 cylinder coils make it easy to provide separate power from independent busses. Dual channel ECU’s and dual fuel pumps too.

It’s the fuel injectors that are difficult. One can provide separate power to each bank of three, but no easy way to provide power to all 6 from either bus.

If there were dual fuel injectors for each cylinder (like Rotax iS) it would be easy!