and dual alternators for me. Installed cross tie solenoid. Accepted the weight to insure safe operation of a electrically dependent system.
+ 1 for what longline said. Secondary system is 8a alternator and small Life battery with crosstie. Came in handy when I accidently left main master on and discharged main battery.
One batt, two alternators is a problem. If you lose the batt, all you have left is half wave rectified AC power off the alternator - this means unhappy electronics. There needs to be a functioning battery in the system to absorb the pulses from the alternator.
There really isn't anything to argue, that's how alternators work.
An important part of the evolving aircraft electronics systems is the evolving electrical distribution to support the new systems.
Robert
I've tested this very situation in my aircraft with dual alternators and a single battery. I took the battery offline by switching off the master contactor, to test whether the alternator(s) would continue providing power. The result was, if the main alternator field is already energized when the battery goes down, then it continues providing power.
If you got a fire, then all your electricity gets shut down, and your motor flies on pmag or magneto.
What am I missing in the discussion here?
The condition stated in the original question...with all electric fuel pumps and ignitions. The ability to open the master contactor without affecting engine operation is a key system test.
The KIS approach to that condition is to wire the ignitions and pumps directly to battery feeds which have no dependence on the aircraft electrical system.
Basic VFR and IFR architecture:
I'll submit three principles, often overlooked while designing grand electrical schemes with many wonderful features.
1. Any pilot should be able to operate it without instruction. Put another way, operation should be self-evident, or the same as any other airplane.
2. The battery feeds should be physically separated from the rest of the wiring, to the maximum extent possible. They should also be separated from each other.
3. The least complex system is usually the most reliable.
Humor a bit of editorializing.
Right now, we're growing a fleet with no electrical commonality. At the same time, we're bringing in more and more non-builder pilots from the traditional GA fleet. E-busses, cross feeds, and switch flipping to maintain engine noise is a recipe for increased accident numbers. Time and time again, the human factor is the stubborn cause we can't make go away.
Physical separation is important. We see a nice wiring diagram intended to isolate problems, but then the builder installs the backup alongside the primary. Doing so makes them subject to the same physical trauma, whatever it might be, and one can take out the other.
As for the least complex being the most reliable, let's go with an analogy. You've made a successful forced landing in a forest clearing 100 miles from civilization, and baby, it's cold outside. The chips are down; without fire and shelter, you're going to freeze to death. Which would you rather have, a chain saw, or an ax?
For an airplane with all electric fuel pumps and ignitions, what are the pros and cons of each option?
60 amp main alternator, SD8 standby alternator on vacuum pad, one battery. Split Main bus and Emergency bus. Aeroelectric book has the setup in one of their diagrams. No time limit this way as with a battery.
Hi Erich,
It?s Bob Nuckolls (spelling). Through Aeroelectric Connection and his various articles, Bob has contributed a tremendous amount to experimental aviation. I?m somewhat following Bob?s z14j architecture myself substituting an SD-8 for the auxiliary 20-amp alternator and inserting the EFII Bus Manager into that architecture. Bob is definitely one of our ?good guys!?
That being said, just because Bob offers a schematic, that doesn?t mean that there might not be component issues associated with the schematic that you need to research and understand yourself. Yes, the electrons will keep flowing from the alternators if the battery fails, but, as Robert correctly mentions, the alternators in absence of a battery deliver a wave form that some electronics like avionics or ignitions may not like. Yes, most will keep operating, but possibly with signal (noise) problems or other issues. Components like lights or fuel pumps are usually not as sensitive.
I should mention that Robert Paisley is an Electrical Engineer (Cal Poly) and has decades of experience designing, producing, and testing fuel and ignition systems for motorcycles, cars, and, over the past decade, aircraft. He definitely knows what he is talking about and is one of our ?good guys,? too. Rather than posting a ?put down? here on VAF requiring a response or pitting one experimental aviation ?good guy? against another, it might be best to call or send a PM or email first. Assuming that Bob would disagree with Robert is a real stretch and is probably not the case.
Robert?s (EFII?s) phone is 951-317-3473, you can PM him here on VAF via rcpaisley, and EFII?s email is [email protected].
I hope this helps,
For an airplane with all electric fuel pumps and ignitions, what are the pros and cons of each option?