Date:         Fri, 5 Dec 2003 17:56:59 -0500
Reply-To:     Edward Maglott <emaglott@BUNCOMBE.MAIN.NC.US>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Edward Maglott <emaglott@BUNCOMBE.MAIN.NC.US>
Subject:      Re: circuit for bridging the batteries
In-Reply-To:  <3FCFF49D.AEA8E7F6@earthlink.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed

Hmmm, this is a good point.  But I am thinking of things I have read that
talk about the one wire in the aux batt relay circuit being a smaller wire
specifically to limit the amount of current going between the 2 batts.

So, if my starting batt is discharged, and I close the relay manually with
my system, how is that different from my aux batt being discharged and I
start the engine?

Now, suppose my starting batt is discharged and I have the relay closed
with my system, and I try to start the engine.  Big load hits the dead
starting batt, and tries to draw off the aux batt through the small
wire.  Does the size of the wire limit the amount it can draw off the aux
batt, or does the wire overload and get hot and burn my van up with me in
it?  Is the amount of load the difference between the 2 scenarios?  If I
run my aux batt totally flat then start the engine, wouldn't that put a
pretty big load on the wire connection and relay between the 2 batts?

Edward

At 09:59 PM 12/4/2003, you wrote:
>Edward, DON'T do it that way. The stock aux bat wiring is not large
>enough to safely allow the aux battery to be connected during starting.
>The starter motor can draw way too many amps for that small wire. That
>is why VW connected the relay in such a way that it is not connected
>unless the alternator is charging. They even hooked the controls for the
>relay to the starter circuit such that it disables the relay when you
>are trying to start. They did this as a double safety precaution.
>
>In other words VW designed the stock aux bat system to prevent exactly
>what you wish to do. Don't simply bypass their protection measures.
>
>You need to upgrade the relay and the wires that connect to it from each
>battery. To do less is very risky. You may get away with it for a time
>but it disaster may ensue.
>
>Mark
>
>
>Edward Maglott wrote:
> >
> > I was looking at a way to hook the aux and vehicle batteries of the Westy
> > together.  I have a charger set up on the aux batt, so that it gets charged
> > whenever the vehicle is plugged in.  I would like to connect the two so
> > that the vehicle batt can share in that charging when needed.  Or let the
> > aux batt boost the vehicle batt when needed.  So I thought, there's already
> > a relay in place to do this.  How about a little switch to energize the
> > coil on that relay?  I tried applying 12V to the blue wire and that did the
> > trick.  So then I started to find a switch to install for the purpose.  Now
> > I am thinking about where that 12V is going to go when it also travels back
> > down the blue wire to the alternator.  Is this a bad idea?  Thanks for any
> > input.
> >
> > Edward