JUst to be clear, the new house battery is  not directly connected to
the alternator. I simplified the description for the sake of brevity.
Here's the actual new setup:

alternator > fat wire > stancor contactor (relay) > house battery.

The contactor is driven off the relay under the driver's seat which
provides 12 V once the alternator lamp goes out, as per usual.

--
Jack "Rocket j Squirrel" Elliott
1984 Westfalia, auto trans,
Bend, Ore.

On 10/14/2012 02:10 PM, mark drillock wrote:
> There is some danger to that as a general suggestion and it should not
> be commonly done because of this.
>
> Connecting another battery with heavy wire directly to the alternator
> runs the risk that someday that battery will be called on to supply the
> majority of the starter motor current! While the new heavy wire could
> support this the next wire segment between the alternator and starter
> motor was never intended for starting current! It is safer to connect
> the new heavy wire from the new battery to the starter post, and then to
> beef up the wire from the starter to the alternator to allow better
> charging of both batteries. The previously linked to product from
> VanCafe fills the role of the beefed up wire from alternator to starter.
>
> Mark
>
>
>
> neil n wrote:
>> That's useful info.
>>
>> I can't state this as a fact, but IMO, it seems the OEM aux. battery
>> setup was designed for low draw appliances. It works fine for that.
>> But. If one plans to install higher draw appliances and/or lots of
>> "bells and whistles" (i.e. digital ice cream maker), as per your
>> comments and observations, IMO, installing a new (fused?) large gauge
>> wire from alternator to new battery(s), is a great start.
>> .............
>> Neil.
>>
>> On Sun, Oct 14, 2012 at 8:04 AM, Rocket J Squirrel
>> <camping.elliott@gmail.com> wrote:
>>
>>> I want to describe an issue I found while working on my van. Most will
>>> probably not have this problem unless they are running an '83 or '84
>>> digijet (1.9) camper van and draw a lot more out of the alternator than
>>> a stock van does. But if this fits your situation, it bears inspecting
>>> for this potential problem.
>>
>>
>>
>>> I found the second problem when poking around in the connector box
>>> located in the engine compartment on the firewall forward of the engine
>>> on the driver's side.
>>>
>>> Bentley 97.56 shows a pair of 12-gauge wires coming off the alternator's
>>> B+ terminal and going to the plus connection** in that box.
>>
>>> When I opened the box I saw that the last inch or so of the wire pair
>>> had darkened insulation, and the connector used to connect them to the
>>> plus connection was nearly black.
>>>
>>> Clearly the heavy load I'd been placing on the wiring had overheated
>>> that connection, increasing its resistance and further reducing the
>>> charge voltage on the engine battery.
>>>