Started January 10, 2007
The electrical system is one place where builders vary quite a bit. There are so many choices to be made. Do you want fuses or circuit breakers? Do you want traditional switches or the full blown system like the EXP-2 bus? Do you want a key switch for your magnetos and starter or two toggle switches with a push button starter? In fact, do you even want an electrical system at all? The first prototype had no electrical system and Bob just hand propped it to start.
I have elected to go with the Bob Nuckoll's system. Bob is an electrical engineer with ton of experience in aircraft electrical systems. I highly recommend you get the Aeroelectric Connection by Bob Nuckolls. In this section, I'll be referring you to a lot of links to articles in the Aeroelectric connection, on how I did my electrical system. Its all already written so I figure "why re-invent the wheel?" Click on each link as you come to it and you will see it come together.
You can get a real good start on all of the main rules that I used for creating an excellent, reliable electrical system by reading this article. I also recommend that you read all of Bob's online articles (he calls them comic books) available on his website here.
I'm going to share what I am installing in my airplane for an electrical system but again, this not the be-all to end-all systems. You choose what you want to install in your airplane and do the research ahead of time to get it right. If you want to copy any or all of this be my guest. I feel its a great system for a simple day/night VFR airplane. If this were going to be an IFR airplane, I would probably add a second alternator and possibly a second battery to the system. To see my instrument panel layout click here and then come back to this page.
I'll be using a fuse block system with a simple toggle switches to control everything. I have decided to use the Key switch with starter function for the magnetos.
The fuse blocks will act as the electrical buses where everything is powered from. I'll cover that in a minute.
Lets start with the Battery and work our way back. Since I have the lighter O-360 engine with a fixed pitch prop, I'll need some more weight forward of the CG (center of gravity) for Weight & Balance reasons, so I'll mount my battery out on the firewall. Builders with the heavier O-470 and O-540 engines, especially those with constant speed props, might need to mount the battery further aft.
As for the battery, my research has turned up a lot of good things about
the Odyssey 680 Drycell Battery:
For the large terminals like the ones on the battery, starter and Alternator "B" lead, I used the techniques shown in this article to make the wires.
From the battery Negative side, I use 4AWG wire to the Forest of Tabs (see 2nd picture below) on the firewall, and from the Positive side, 4 AWG wire to the Master solenoid (silver). The other solenoid (black) is the starter solenoid and I have a 4 AWG wire from the Master solenoid to the starter solenoid. (Note: I later moved the starter solenoid up beside the master solenoid as it was in the way of my throttle and mixture cables). Also, a braided ground strap will be added later, from the forest of tabs bolt (negative side of battery) to the engine case. Do not ground the engine through the engine mount alone! The rubber mounts will insulate the engine. Without a proper ground, your alternator, starter and some senders will not function properly.
Back when I welded up the fuselage, I welded on some .080" thick steel tabs
to the firewall tubes. Here is a picture from about a year ago showing
the .080" thick steel tabs:
Wow - talk about a blast from the past, that was a long time ago
:>)
Now that it's time to install the battery, I have attached some 3/16" thick
aluminum strips, 2" wide and 24" long to the welded tabs. This will give
me some reinforced mounting points for the battery as well as the master
and starter solenoids. Here is a picture from the backside of the firewall
showing the battery/solenoid reinforcement strips:
There are a few things to take note of in the above picture. Since
the battery is an item that may need to be removed once in a while for
replacement, I took the time to install plate nuts where the battery box
bolts on. The solenoids are just bolted on with regular nylock nuts.
The rectangular brass thing in the upper right -hand corner of the
picture is the "Forest of Tabs" grounding system available from
B&C Electrical Products.
There are 24 tabs soldered onto a brass strip to attach ground wires
to. This allows a single common ground point from all of the various components
to attach to. The forest of tabs is bolted to the firewall with a 5/16"
brass bolt. The negative side of the battery is attached to this same brass
bolt on the engine side of the firewall.
Having everything grounded to the same location is one of the rules outlined in the Aeroelectric Connection. It basically eliminates a lot of problems with things like improper grounds, radio noise, ground loops (not the kind done on the runway, but the electrical kind), etc.
One of the places that I think a lot builders neglect is the firewall pass-through for wires and tubes and such. You must have a safe, fire and smoke proof way to get wires from the engine side, to the cabin side of the firewall. On many of the homebuilt airplanes I've looked at, all I see is a plain rubber grommet where the wires or hoses come through the firewall. Engine compartment fires are rare, but do happen on occasion. The thought of being at 3,000 feet and having smoke and flames entering the cockpit scares me. So I'm doing all that I can to buy myself some time to get safely on the ground should an engine fire happen. Bob Nuckolls did an excellent article on firewall penetration.
I have elected to use a system made by
EPM.AV. Here
it is in the upper part of the picture:
It is a stainless steel pass-through that gets attached with stainless steel
rivets and has a fire barrier sealant between the firewall and the piece.
The wires, hoses, etc. pass through then get wrapped with a piece of
fire-sleeve inside and out.. Then the ends are sealed with some more fire
barrier sealant.
Here is the same pass-through after all of the engine sensor wires have been
pulled through and the properly protected:
As you can see, there is a piece of firesleeve on the outside held in place
with some hose clamps. What you can't see is that there is another piece
of firesleeve that has been slit down the middle lengthwise and then slipped
inside the outer piece, creating a tight fit for the wires. Finally,
the end is sealed with fire sealant as shown.
I also bought the stainless steel heater box from the same folks. You can
see the stainless steel heater box in the picture below:
Do not use the aluminum ones that some folks
are using. In an actual fire, the aluminum ones last
about 5 seconds and then you have a big 2" hole with flames and smoke shooting
through it and into your cabin. Also of note in the above picture,
is that I have relocated the starter solenoid up beside the master solenoid.
I now have a good clear spot for the throttle, mixture and carb heat
cables to come through.
Click here to go to Electrical System Page 2