Design suggestions - Single alternator electically dependent aircraft

[walkman]

I just ordered my GRT and Gemini to redo the panel in my -6. I'm off the UK for a couple of weeks so in between chasing cyber criminals across the EU, Russia, and The 'Stans and writing a paper for one of my classes, I need to design the electrical system.

I'm going from a traditional steam gauges aircraft to all glass. In addition I recently installed a half EI/half mag system. Now that I've had a taste of EI, and because I'm going to be building a robust fault tolerant electrical system, I might go full EI.

Regardless, I'm looking for some pointers. This will be a single 60A externally regulated alternator. I am thinking 2 identical batteries (one gets replaced each year). Probable in the 17-20 Ah range. I want to be able to survive an alt failure and a simultaneous battery failure, and be able to run my major electrical systems as long as there's fuel in the tanks.

I plan on starting off one battery only, and probably need an automatic way to switch or to run off either battery.

Where to start? I have borrowed a copy of the Aeoelectic book, I'll be reading that.

[DGlaeser]

Here is what I did for my electrically dependent Subaru:
http://users.wowway.com/~glaesers/electrical_plan.htm
Probably more detail than you want...

It is close to what became Z-14 in the AeroElectric set of architectures (I did mine first). So I suggest start with Z-14 in Bob's book and go from there.

I suggest that any sort of auto switching is just another point of failure. Battery failures are extremely rare so don't overly complicate things trying to cover situations that rival (or exceed) winning the lottery for probability.

I always start on the main battery, while my isolated E-bus is running electronics (EIS) during the start. Normal ops have the batteries in parallel - being charged by the alternator. For emergency (alternator out) ops, it is E-Bus ON, both battery masters OFF. One battery runs the engine, the other does the E-bus. The engine can be run from either battery.

[rleffler]

Before I made the decision to go with Vertical Power, I was going to implement Z-14 in my RV-10. If you talk with Bob, he'll tell you that he thinks Z-14 is overkill for an OBAM aircraft. Like Dennis mentioned, it's a good design. I think he recommends Z-11. You should subscribe to his mailing list on Matronics. You'll get all kinds of opinions and some directly from Bob as well.

I implemented a VPX/Pro. I also have a 2nd alternator and two batteries. The endurance bus can be completely isolated or I can put the two batteries in parallel if I need the extra cranking power. If you are looking for options, you may want to take a look at Vertical Power's products.

There are plenty of options that you can implement. Now is the time to spend planning the design. This was the part of the build I enjoyed working on the most.

bob

[jjconstant]

I used a single alternator (B & C) and two PC680 batteries with independent master switches and independent grounds tied together. I start the engine with both, taxi and takeoff on both. Once in cruise I turn one master off which completely disconnects that battery from the electrical system. If there is a failure the plan is to turn off the alternator and flying battery and turn on the other battery while keeping the alternator offline. Shed the loads appropriate to the situation and fly on to an appropriate place to land using a fully charged and healthy battery.

[9GT]

Originally Posted by jjconstant

I used a single alternator (B & C) and two PC680 batteries with independent master switches and independent grounds tied together. I start the engine with both, taxi and takeoff on both. Once in cruise I turn one master off which completely disconnects that battery from the electrical system. If there is a failure the plan is to turn off the alternator and flying battery and turn on the other battery while keeping the alternator offline. Shed the loads appropriate to the situation and fly on to an appropriate place to land using a fully charged and healthy battery.

That's also the way I have my -10 set up. I'll only use one battery at a time though unless I need a little extra cranking power.

[ronschreck]

Originally Posted by walkman

I am thinking 2 identical batteries (one gets replaced each year).

I have been running two Odyssey PC625 batteries on my dual EI setup. No need to change batteries so often. Mine are going on 5 and 6 years and still strong. I used AeroElectric Z-14 with some modifications.

[humptybump]

I am about 30% into my panel redux. I have the single alternator and two LiFePO4 batteries - one is 27AH and the 'backup' is 17AH. The combined batteries are less than half the weight of a single PC680.

As for "switching" solutions, I read a lot on VAF and implemented a diode based automatic fallback solution.

[walkman]

My reasoning for starting on one battery only was that in the event of some sort of failure following take off, I would have at least one battery at full charge.

I do plan on flying the airplane IFR

Additionally, I was planning on having the necessary electronics NOT be dependent on a functioning battery contactor.

[Brantel]

You don't get much simpler than this one:

(Note: I think Paul added a diode on the aux battery feed to the essential bus that is not shown in this pic)


My new retrofit will have something similar with the exception of the following:

VP-X Pro provides the main & avionics bus function/switching and over-current protection.

I won't have a feed from the essential bus to the avionics buss. Don't see the need since all the essential items will be on the essential buss.

I won't have a main battery feed to the essential bus. If I am already running from the essential bus, the main battery is dead and the alternator has failed anyway so I don't see the need. If I don't have this feed then I don't need the diode between the main and essential buses.

[airguy]

Why not install the 12-amp standby alternator on the vacuum pad, if you're going to an EFIS that doesn't need vacuum? It won't handly full load, but it will handle bare-bones flight-critical items.