Date: Thu, 15 Jun 2000 22:52:16 -0700
Reply-To: bpchristensen1@home.com
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Brent Christensen <bpchristensen1@home.com>
Subject: Re: 2nd batt. charging and relays. The whole truth
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Whew! Do I feel better now. :-)
For about a year now, I have been stressing about my wimpy 20a relay and 12
awg wire setup (though I have a 75a relay and 8 awg wire ready to go, I
haven't found the time to install it). Now I can sleep at night, forget
about "upgrading", and someday instead use the 75a relay to power the cool
set of 200w Hella driving lamps I have sitting in my garage....
Thanks for the discussion everyone - I followed it with great interest.
Beckett's argument supports what I have always intuitively believed, but
could never prove in scientific terms. (One of the problems growing up as
an EE's son... familiarity with concepts but no true scientific knowledge)
<g>
Brent Christensen
'89 GL Syncro Westy
Santa Barbara, CA
----- Original Message -----
From: Beckett Cantrell <THX0980@aol.com>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, June 15, 2000 1:33 PM
Subject: 2nd batt. charging and relays. The whole truth
> 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
5amps( 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
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