On Mon, 15 Apr 2013 09:07:23 -0500, "Pete C."
wrote:

I think that you are being excessively conservative in talking about a
15 amp charging rate into a large battery bank though :-)

Especially from an alternator in a semi which should be good for 200A+.

Doesn't matter how big the alternator on the truck is - 125A to 200A
is normal, but they make 400A truck alternators for specialized
purposes - big honking mothers.

Point being, If the charge line going back to the trailer is only
10-GA wire and you try pumping 400A through it, you'll have it glowing
like a lamp filament - for a few seconds till it grounds out and
blows, and takes any wiring harnesses nearby with it.

Or better yet, melts the nylon air brake lines on the truck and kills
the brakes. Or goes right next to the fuel lines...

The norm for a trailer with a battery and liftgate is 1/0 wire, and
they do make 1-pole and 2-pole trailer connectors and curly-cords for
that. You can charge them at 100A no problem - except most batteries
can't take that much charge current at once. They tend to blow up.

You rig a 500-MCM charge line back to the trailer and get a set of
quick disconnects from the tractor to trailer rated to carry that
much, then you can get the charge feed straight from the 400A
alternator.

Oh, and don't forget a matching ground path good for 400A back from
the trailer battery, or the Fifth Wheel latch assembly and the trailer
Kingpin could get un-annealed and fail - last I checked Semi's don't
have Safety Chains... Or hot enough to light the grease on fire. Or
arcing damage. Gee, wonder which would cause it to fail first...

-- Bruce --