Firewall Layout

As the basic electrical wiring, components, tools were arriving, I started to lay them out on a mock up firewall. It did not take long for me to realize I am going to be running out of room. They included the battery, the master contactor, starter contactor, all the external regulator controls for both of my alternators (L60 and SD8), Princeton fuel probe controls, terminal blocks (switched & un-switched), ground terminal block, the electronic ignition control box, engine monitor unit and the manifold pressure monitor box. I have to blame the cluttering culprit to the external regulators for both of my alternators. If I were to do it over again, I would have bought the internal regulated alternators. Four of the 11 components that mount onto the internal firewall belong to the two regulators!

Battery

I started planning my electrical system from the battery. I bought the same battery most Cozy builders use (PC680) as my starting point. In order to keep the battery securely in place, I must first fabricate a strap of some sort to hold it in place. I started with 0.050" thick 2024 T3 aluminum sheet and cut out a 4" strip. Then I made 4 90 degree bends to it. I feel I must make it really snug such that there is absolutely no movement between the battery and the strap. I'll be the first to admit that I am just not a good sheet metal bender... I forgot to add the thickness of the metal sheet. As a result, my strap was too loose. Trial #2 turned out to be too tight...

I gave up and decided to make the strap out of 4 layers of BID. They fit perfectly. (Refer to the pictures below).

Mounting the Battery

Now it's time to bolt the battery against the fire wall and of course, it does not sit right. Both the firewall and spar surfaces are not flat nor sitting perfectly 90 degrees (as the back of the battery). I ended up adding 4 layers of bid on the firewall for backing and a raised step for the battery to sit on.

Building the raised step for the battery was a bit more complicated than expected. First I put packing tape over the lower 2" of the battery. Then I strapped and shimmed the battery against the firewall (after the BID cures). Then I formed a flox perimeter (or filled the gap) under the battery with wet flox. After the flox cured, I removed the battery.

You can see the flox rim I made under the battery.

Add some pour foam inside the flox cavity and shape it to a flat step. I got a bit carried away with the pour foam here...Actually, I forgot how much pour foam tends to grow.

Once the pour foam hardened, I carefully sliced and sanded the excess off. Then I followed with 2 BID of glass on top.

Here's a picture when the battery is finally strapped in place!

Note the two miniature levels I used to make sure the battery is sitting straight and level relative to the rest of the plane.

Terminal Blocks (Switched, Un-switched and Ground)

One of the key functions of a fuse block is to protect the wires from over-heating. Therefore, they should be located close to the power source (battery) prior to distributing the power onwards. I picked the idea from Tim Andres by mounting my switched, un-switched and ground terminal blocks onto the battery strap. I did so by glassing 4 flat-based studs (discussed later) onto the strap.

If you look close, you can see that there are 2 separate terminal blocks (switched and un-switched) held down by 2 flat base studs each.

My next step was to add the ground terminal to the battery strap as well. I bought my ground terminal strip from SteinAir and it is somewhat flimsy. In order to add more rigidity to the terminal block, I cut up a small strip of aluminum (1/8" thick) that fits the foot print of terminal strip. Then I floxed and glassed the aluminum onto the side of the strap (as shown).

Once cured, I drilled and tapped two 8-32 threaded holes into the embedded aluminum hard point. Then I bolted the ground terminal to the hard point as shown.

Finally I stumbled into a discussion in VansAirForce forum that suggested an alternative from McMaster Carr - a perforated base stud. I decided to look them up. To my disappointment, they all have a large base (1 1/2" diameter) and cost from 70 cents to $1.30 each. While experimenting with it, I noticed the word 'Rotaloc' stamped on the bottom side. Curiously enough, I looked them up on the Web. It turned out they are the manufacturers of the part for McMaster and they come with all types of base shapes and sizes. In addition, the studs also come with different threads and lengths. They cost - 33 to 44 cents each. A quick phone call got me several models and sizes in 3 days.

As shown in the picture, the left most perforated stud is from McMaster Carr, the top center is a carriage bolt from a local hardware store. The top right click bond is from JD Newman. The front 3 are perforated base studs with a much smaller perforated base and different thread size and length I bought from Rotaloc. I decided to use the Rotalocs for my through hole anchors for my firewall electrical components and devices.

Here's a picture of how I prepared them. I first drilled a 7/8" round step using a Forstner bit. The step is just deep enough for the thickness of the perforated base. Then I switched over to a 3/8" Forstner bit and drilled a second step to accommodate the stud base. Then I followed with a drill bit through hole for the threaded stud (as shown in the picture).

Once I am certain with the stud location, I added wet flox to the perforated base, pulled the base in tight by putting a large washer and a nut on the other side. This will squeeze out the excess flox through the perforated holes. I added extra flox to fill the entire cavity and covered it with 1.5 x 1.5 BID (2 layers). Then I peel plied and let cure.

Here's a picture of my fire wall using mostly the perforated base studs through the fire wall. They include the battery, the master contactor, the starter contactor, all the regulator components for my main (B&C L60) and backup alternators (B&C SD-8), the ANL fuse block for the alternator and my electronic ignition controller. The three heavy duty lugs in the middle are from Blue Sea System that carry the power to the engine compartment - yet isolating the post from the firewall.

You can see, my wiring process is about to began... 

Routing the Wires

It is good practice to route the wire in a manageable bundle such that they can be traced, repaired or modified as needed. Since I am not experienced enough to foresee how the wire routing will be, I decided to use stick on wire holders (on a temporary basis) to guide my initial routing. I soon realized that these stick on wire holders were difficult to remove, plus they leave a messy glue residue on the fire wall.

To prevent this from recurring, I lay blue tape strips on the fire wall first to block off the glue residue (as shown). That way, I can re-locate the wire holders as I go along without any residue effect. Here's the preliminary wiring harness - starting to take shape.

Final Cable Tie Mounts

I finally settled on one of the most common cable ties (as shown - Greenlite Cable Ties GMB-4A). It comes with an adhesive back as well. However, I removed the adhesive back (heat it up with a heat gun and the back peels right off). Then I rough up the bottom of the cable tie mount and its mating surface slightly with a 80 grit sand paper. Then I epoxy it in place. Initially, I used my glassing epoxy. As wiring efforts proceeded slowly, I became impatient - I just used 5 minute epoxy because it cured quickly. Surprisingly, these cable tie mounts held their places very well. I have pulled and tug on them while strapping the cables to it with my splice knots. Only two came off (out of ~100) so far. With those, I put a small 4-40 counter sink screw through it for added security. These mounts will not be coming off!

I chose this cable tie over the click bonds because its about 1/3 the weight of the click bond, its has a lower profile, takes less real estate and its cheap! You will be using many of these cable ties for your Cozy.

Engine (EIS) and Manifold Pressure Monitors

As more and more equipment arrived, I found there are more and more components needed to be packed into the battery compartment. The latest are the engine and manifold pressure monitors. Since my GRT EFIS will be reporting my engine status, there really is no need to place the engine monitor controller on the IP. It makes more sense to mount it in the Battery compartment (shorter wiring). In addition, the manifold pressure monitor (small black box) receives information from the engine and reports it to the engine monitor. So, it makes sense to placed the manifold pressure monitor in the battery compartment as well. I found the real estate in the battery compartment is getting limited - quickly.

I do like to keep the center part of the compartment open for unexpected harness or the like between the front and the back. I decided to build a small box like holder for both the engine and manifold pressure monitors. Here's the picture of the box to hold my EIS unit. 

Battery Compartment Wiring

As I moved forward to my wiring, the battery compartment started to get loaded. Here's a updated picture of my battery compartment.