FWF Electrical & Ignition Wiring

[robcaldwell]

Just curious if anyone has a diagram with AWG choices for their firewall forward electrical and ignition systems (not engine monitoring leads and misc)? The RV-10 FWF kit I purchased has included all but the electrical and ignition wiring details. I can and do reference AC 43.10 for wire gauge sizes based on usage, just curious what others are doing.

For example, I've heard some say they use a 2 AWG from the + battery lead to the battery contactor. 2 AWG seems excessive. I've seen other references to 4 AWG for the same run. Seems like this should be standardized. Maybe it exists and I've missed it somewhere.

Specifically looking for:

- +Battery terminal to Battery Contactor
- Battery Contactor to Starter Contactor
- Starter Contactor to Starter
- Battery Contactor to Alternator
- Battery Contactor to Panel Bus Bar
- Battery ground to airframe
- Engine ground to airframe

Thanks!

(Forgot to mention... I have the Tony Bengelis books, Bob Knuckles Aeroelectric Connection, and several aircraft wiring books. Surprised there are no "basic" or "suggested" diagrams in those... EDIT: Diagrams DO exist in the back of Aeroelectric Connection )

[AZBearhawk272]

Rob,

Having just finished that task.
in the order of your list:
2,2,4,6,10,2,4 AWG

Some depends on length of run. I tried to keep voltage drop to starter negligible. That makes a huge difference in cold cranking. With respect to running a full electrical
panel and ignition, my drop at the interior buss at the fuse panel
is less than .2 VDC. With most system load On.

At least it works in the garage.
Looks correct under the cowl.

KD #272

[zkelley2]

What amperage alternator are you running and what are your maximum electrical amp loads?

[robcaldwell]

BC460-H 60amp (Main) & BC410-H 20 to 30amp (B/U). Still working on max amp load, but not expecting more than 30.

[AZBearhawk272]

60 amp alternator.

If all the loads were all on at once, worse case....
52 Amps load.
Normal approx 35 Amps.

KD #272

[Ed.Meyer]

If you haven't already, I would suggest you read the Aeroelectric Connection by Bob Nuckolls. It has about everything you would need to know about airplane wiring including lots of discussion about wire sizes. You can download the book aec_12a.pdf which has 18 chapters plus an appendix with various power distribution wiring diagrams. We used number 4 wires from battery through contactor to starter. Works good.

[robcaldwell]

I am in the process of reading Bob Knuckles book, Aeroelectric Connection, but have not reached the appendix section with wiring diagrams. Looks like the "Z12 Dual Alternator, Single Battery" diagram will suit my desired outcome. Thanks for pointing this out, Ed.

[whee]

Bob Nuckolls book is a good one, a very boring read but solid information. I used it referencing the pertinent chapters when needed. We sized our wires according to AC 43.13. We used welding cable for our battery leads as suggested by Nuckolls. I'd need to double check but I'm pretty sure we used #6 for battery leads (dual batteries) and to the starter. From the master to the power buss we used #8 tefzel. The alternator lead is #8 tefzel (60A). Hmm, I need to double check those sizes.

It ia always good to see how others did things. My suggestion is to size the wires yourself using appropriate references.

[svyolo]

AC43 is totally appropriate and in line with every other DC thing I have done. I think generally you want your grounds to be the same size as your power lead, including battery ground and engine ground.

I have seen a few vehicles burn to the ground (or waterline) because the starter wire caught fire, including a friends jeep that I was sitting in as he cranked away at the starter. I would never cheat a wire size on a starter wire after that!

[svyolo]

I made up my oil lines,or 2 out of 3 yesterday. I almost ordered premade once from ACS, but they are a bit spendy. Then I thought what if one or two didn't work as designed? So I bought parts. Good thing. AN8 fittings are really bulky. Even straight ones extend out 3" before the hose starts. Luckily I just eat one or two fittings, instead of 1 or 2 120 dollar hoses.

[marcusofcotton]

If you want to avoid magnetizing the frame (and yes you do), don't use it as a current carrying conductor. Especially larger currents, starting being the whopper. That's not to say don't ground the frame, do ground it, but also run appropriate size grounds directly to your loads.

[Sebastian]

This is interesting. I haven't found one mention of tin coated copper wire. When I was working on my FWF wiring I consulted one of our electrical engineers (who I found out had worked a stint at Boeing) about wire sizes for starter and alternator. We discussed welding lead for started but he told me that if I went with the tin coated copper that I could reduce the wire size and weigh. Apparently when you go tin coated the standard wire AWG and current ratings go out the window. I wound up using #4 tin coated from battery to the starter approximately 9ft and #8 tin coated from alternator to battery (60A Alt) and #10 regular copper to my main bus bar and my avionics bus bar. Just food for thought for what it's worth.

[robcaldwell]

This is the schematic that I will work from. Dual Alternator / One Battery. This comes from the the Aeroelectric Connection site. A little cumbersome to locate your desired plan through this file tree. Probably best to choose the schematic you need from the book, then get the digital version here: http://www.aeroelectric.com/PPS/Adob...itecture_Pdfs/

[Bcone1381]

I've become quite familiar with this book and you'll want to become familiar with the associated forum. The author is very active there. Go to:

http://forum.matronics.com

Then go to "AeroElectric-List" You'll normally have good answers in 24 hours. (These guys are the Experimental Aircraft Electrical System Gurus.)

[robcaldwell]

Thank you, Brooks! This is such a better forum then the one posted at http://www.matronics.com/subscribe/. I subscribed, then unsubscribed that one fairly quickly. Very outdated. Knuckles should update this on his http://www.aeroelectric.com website.

[zkelley2]

If you want to avoid magnetizing the frame (and yes you do), don't use it as a current carrying conductor. Especially larger currents, starting being the whopper. That's not to say don't ground the frame, do ground it, but also run appropriate size grounds directly to your loads.

It'll magnetize anyways just from the static build up from flying.

Every starter uses the engine... and therefore the frame as a ground.

[schu]

Rob,

Having just finished that task.
in the order of your list:
2,2,4,6,10,2,4 AWG

Some depends on length of run. I tried to keep voltage drop to starter negligible. That makes a huge difference in cold cranking. With respect to running a full electrical
panel and ignition, my drop at the interior buss at the fuse panel
is less than .2 VDC. With most system load On.

At least it works in the garage.
Looks correct under the cowl.

KD #272

That looks plenty reasonable to me