Got an experimental plane I'm moving the battery back to solve a balance issue. My question is: does the extra distance from the starter make a larger wire gauge size necessary? Battery on firewall uses 4 AWG. Should I bump it up to 2 AWG for the distance?

I know many have talked about certified planes with battery's in the extended baggage. Is this done by STC? Do they up the wire size?

Almost more important than #4 or #2 is the type and conductor COUNT.
Wire / Cable can be found with 7 strands - 19 strands and multiples of same.
Fewer strands makes for stiff wire / cable with less current capacity due to Internal Resistance. (IR)

Welding cable is very flexible and #4 = ~~415 strands while #2 = ~~650 strands.
Some may / will argue against it. Newer Aviation wire and cable is quite stiff, especially larger sizes.

http://www.aeroelectric.com/articles/bat_cabl.html

At one time - new tail-wheel planes - and maybe others - were built with ALUMINUM battery cables.
Apparently the FAA had not learned the lesson from the housing industry.

FIRST need to know how much current your starter requires.
Especially on a possibly longer cold start.

Best for now
Chris C

Here are a couple of links you may find useful:

http://www.skytecair.com/Wire.htm

http://www.periheliondesign.com/fatwires.htm

Treefeller wrote:Got an experimental plane I'm moving the battery back to solve a balance issue. My question is: does the extra distance from the starter make a larger wire gauge size necessary? Battery on firewall uses 4 AWG. Should I bump it up to 2 AWG for the distance?

I know many have talked about certified planes with battery's in the extended baggage. Is this done by STC? Do they up the wire size?

Most of the certified planes with the batteries in the extended baggage already had the battery there - its the extended baggage that is the STC - the battery was put in that location at the factory.


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Barnstormer wrote:Here are a couple of links you may find useful:

http://www.skytecair.com/Wire.htm

http://www.periheliondesign.com/fatwires.htm

Thank you Barnstormer, that Sky-Tec link was very helpful.

generally I use mil spec 16 strand which is a tinned copper with polyethylene insulator. Was just wondering if it was common to bump up in gauge for longer runs.

There are some nice flexible automotive wires you can get some places like summit racing, but the question is the insulator material. Electrical fire in flight and noxious fumes not good.

I never have seen the chart. Thanks Barnstormer. The Pawnee battery is in the very back of the fuselage to counter the extra weight in the hopper on takeoff. Still have to use most of that big spring trim. The wire is as big as what was on the old six volt systems or what is on a diesel truck. Even with that one had to bump the starter to get a half turn of the prop. Lots of line loss. The O-540 was a loose engine and started easily.

I just checked the Cessna 180/185 service manual for 1969 through 1980 models for an example of what was used. For the 12 volt models they used 2 gauge wire. Bogart Aviation, which sells low loss STC'd cable kits for these aircraft publish that their kits are 1 gauge wire. Hope this is helpful.

Tim