Beckett,
Good explanation about the charging capacities with
different wire sizes.

I think a pretty effficient installation is the one VW factory-
installed in some of the U.S. vanagon weekender camping models.
The ones with the small electric-only cooler box.
There VW used a relay and 6.0 metric mm2 wire.
(a standard 8 awg is close but slightly larger)
1991 Bentley page 97.34a
 #8 gauge is good for 15 ft. and 50 amp charging
 (according to Sure Power chart).
So that would provide pretty good recharging for the aux. battery.

If one desires a more battery-friendly system with
more efficient charging of the aux. battery without
affecting the main battery,  I suggest the
Sure Power battery isolator.

Harald
'90 westy

> From: Beckett Cantrell <THX0980@aol.com>
> To: vanagon@GERRY.VANAGON.COM
> Subject: 2nd batt. charging and relays. The whole truth
> Date: Thursday, June 15, 2000 1:33 PM
>
> First, I'm really supprised that among all of the list members, there is
not
> one single Electrical Engineer who steped foward to explain this relay
> delema. So I'll give it to you in a nut shell: Guess what folks, if your
aux
> batt. is deeply discharged, and you're running 2ga. wire and a 75amp
relay,
> the batt. will most likely draw 75 amps(or whatever your alt. can put
out) at
> initial surge. But if you're running, lets say, a Hella relay, rated at
> 15amps, with the wiring provided, and with the same deeply discharged
aux.
> batt., you are most likely gonna draw about 12amps at initial surge, and
much
> lower after a short period of time. It's all related to the Gauge of the
> Wire. Really. Don't buy it? Try this: Take that same deeply discharged
batt.
> and run a really, really tiny gauge wire directly from the positive post
of
> your cranker batt., to the positive post of the afore mentioned
discharged
> batt. Now start the engine. Did the wire smoke? Have the flames reached
the
> cockpit? Are you searching for that fire extinguisher(that is also
probably
> deeply discharged!)? NOPE. Your dead batt. will draw what the wire can
> provide. Still don't belive me? Okay, lets see what VW did from the
factory:
> On older models equipted with dual batts, the relay was rated at 15amps(
I'm
> holding the original one out of my ' 79 Delux in my hand as we speak) and
the
> wire from said relay to the aux batt is 12ga. Believe me folks, nothing
can
> suck down a batt like the old style Dometic 12v/120v fridges found in the
> pre-Vanagon Type 2's, and even when these batts are totally discharged,
> starting your eng. does not cause a pyrotechnic display. If it did, VW
would
> have been litigated out of existance by now. If that still doesn't
convince
> you, well just flip through the pages of  Brightons Studies in Electron
Flow
> ( My God, how I loathed that damn book when I was in college...) to get a
> clearer picture. Your dead batt will only suck up as much as much juice
as a
> given wire will flow. The batt. is not an active device, like an electric
> motor, but a passive one, and will not suck your cranking batt dry at
> start-up (Unless you are running Massive gauge wire to the aux. batt.
That is
> exactly why VW went with smaller relays and wire gauge.) Think of the
set-up
> as a "trickle charger". Okay, enough already.
> Beckett