Date: Mon, 6 Aug 2007 15:04:15 -0700
Reply-To: Mark Drillock <mdrillock@COX.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Drillock <mdrillock@COX.NET>
Subject: Re: Deep cycle batteries, voltage regulators, and eating cake
In-Reply-To: <20070806213018.IDW1354.eastrmmtai112.cox.net@eastrmimpi03.cox.net>
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Now you have proven that the alternator is not the problem and the
wiring is.
You still didn't say what year you have but clearly pre 86. The 86 and
newer has a massively larger cable between the starter and battery and
this is the longest part of the charging wire run from alternator to
battery. The most feeble part in 80 to early 86 models is the 2 smallish
red wires that carry all the current from the alternator, first to a
stud in the engine compartment black box and then on to the starter
motor post. This was improved in late 86 and again in 88 with a
different path of much larger wire.
If I were you I would first examine very closely the 2 red power wires
from the alternator and also follow them to their other ends. I have
seen more of these cooked than you would think. They are often cooked at
the ends hidden inside the engine compartment wiring box. VW increased
the current capacity of this circuit by 250% in later years and that is
what I would do on yours. Run a new 8 gauge wire from the alternator to
the starter motor, using soldered on wire ends made for 8 gauge wire and
5/16 bolt hole. This will likely cure most of your problem but if you
measure the voltages at the starter motor lug first you will know how
much of the drop is there. Test unloaded and loaded, as before.
To get the best voltage at the aux battery I would run another wire from
the starter to the aux battery, letting the aux battery and relay get
charging power from a place closer to the alternator and less affected
by the other vehicle loads.
Mark
Geza Polony wrote:
> OK, tests in. There's a voltage drop all along the way, but grounds are good.
>
> At Alt, no load 14.15 vdc
> At Alt, loaded 14.03 vdc
> Alt to ground, same readings
>
> At vehicle battery, across terminals, no load 13.73-75 vdc (.42 drop)
> Vehicle battery, across terminals, loaded, 12.82-85 vdc (1.21 vdc drop)
> Vehicle battery to ground, no significant difference
>
> At aux battery across terminals, no load, 13.17 vdc (.58 drop from vehicle
> battery, .98 from alt.)
> Aux battery across terminals, loaded, 12.32-39 vdc (.5 drop from vehicle
> battery, 1.71 from alt.)
> Aux battery to ground, no difference.
>
>
> The worst problem here is what I suspected, a more than 1.5 volt drop
> between alternator under load and aux battery under load. The more you load
> it, the worse it gets. (I was using high beams, AC, and fridge.)
>
> This is with the stock 23 year-old wiring and relays, but upgrades to
> grounds. I doubt if any battery set-up would work right given these conditions.
>
> Any idea what an acceptable voltage drop would be using new 6 AWG wire and a
> new OEM-type relay? It seems like ideally, you could get 13.8vdc at the aux
> battery under load--but how likely is that to happen?
>
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