Monday, February 16, 2009

The wiring plan

My goal for the winter (i.e. -- frozen hangar) months was to get my head around an electrical system architecture for the RV-7A. I think I'm on schedule. Today I finally sketched out a wiring diagram utilizing the VP-50 system from Vertical Power. You'll have to click the image to enlarge it.

I won't go into the whole Vertical Power sales pitch because it's a category on the blog here now and you can click it and go read for yourself. I will say that it really does make wiring simpler. First of all, my shortcoming as a builder is being organized enough to buy all the various switches and gizmos that I'd need for a traditional system. Since I installed the Vertical Power VP-50 unit a few weeks ago, I've basically done all that.

I also bought the wiring harness which provides me with the right wire size. I'll have to do some crimping of D-Sub and, of course, I'll have to run the wires, but a lot of work is already done for me.

The diagram above is still a work in progress, but it gives you an idea (if you can read these things) an idea of what I'm up to. Since my Dynon D100 has an internal battery, I'm not wiring a backup circuit for it. The battery is the backup circuit. Same for the GPS (I use a Garmin 296, which I realize won't get me invited to the cool kids' party at Oshkosh, but that's OK).

But I have planned on a backup switch for the fuel boost pump and I'm thinking about one for the flaps. I'm also planning on a second, smaller alternator as a backup but I won't install that until later, when there's more money. For now, I'll run a wire for it out to the engine compartment and tie it off.

And I've still got to look up some more specs on the Lightspeed electronic ignition. So what do I have to buy now? A master bat/alt switch and a starter switch. Oh, and an alternator. I'm leaning toward the Plane Power alternator because it has an internal regulator and overvoltage protection and that's just so much wiring and extra components I don't have to buy and install. I'm all about simple on these things.

Other than that, I've got to buy a bus block (I have one on the way from B&C, but I need one more) and that should do it.

When you first develop your electrical system, you fill out a load planning worksheet from Vertical Power. This makes it easier to figure out what's going to go where. Then, all you have to do is crimp a D-Sub terminal on the proper wire, insert it into the receptacle on the control unit, run it to the device and, voila! It's so simple, even a blogger can do it.

Here's my load planning spreadsheet. I haven't figured out yet what is going to be on the switch unit that actually goes in the panel and connects to the control unit. My very important avionics, however, will be assigned to switch 1 (on the far left) so that if an alternator fails, I simply flip the switch down, which brings the (soon to be installed) backup alternator online. I then flip the rest of the avionics off with one switch and I've taken care of load shedding.

I'm just a VFR pilot. I don't fly at night (although I might a little), so backup electrical systems aren't critical to me. But if I'm on a cross country flight and an alternator goes south, I should be able to complete the journey or -- at the very least -- get the plane down on my terms. Since I'm using half an electrical ignition system, having the backup alternator allows it to keep working without a problem.

And until I get the backup alternator put in, I can certainly hobble to the nearest airport on the strength of the left mag.

Feel free to offer your comments.


  1. Bob, It looks good so far. Backup power for the flaps may not be necessary since you can takeoff or land with or without them....ask me how I know. I will email you a few ideas tomorrow. Kev

  2. Hi Bob,
    Nice job! Here are a couple of comments...

    You said you might do a little night flying so do you need a circuit for some additional interior lighting?

    If you change J8-20 for the intercom from switch 3 to switch 1B (or ON) then you can still talk to your passenger with the avionics switch off. Katie and I talk on the intercom before I start the engine/avionics (we sit tandem though). Its really nice to be able to easily change the circuits to match the way you use the airplane.

    The Wing Nav and tail lite amps looks high. (7.2amps). I can run all three nav lights on a 5 amp circuit on my RV.