At 08:36 5/10/99 -0700, Glommen, Jon wrote:
>I have an '86 Vanagon Westy 1/2 camper that has an aux battery. I don't know
>if it was fitted from the factory this way or if the previous owner did
>this.
>
>Assuming it is a factory installation, how does the battery cut-off relay
>work? Is this one of those battery isolators? I don't know how those work
>either.

Jon, the factory relay connects the two (house and starting)) batteries
together whenever the engine is turning.  At other times the two are separate.

A battery isolator is a pair of large diodes connected so that the center
(charging) terminal can supply either or both connected batteries, but that
neither battery can supply the other.  Advantage is that there are no
moving parts or mechanical switch contacts.  Disadvantage is that the
device dissipates roughly 25 watts per 50 amps of charge rate, and that the
regulator sense lead must be hooked to one or the other battery to provide
charging information to the alternator.  The snag here is that the battery
providing sense info is not necessarily the one with the lowest charge; so
charging times under some circs will be artificially long.

david
David Beierl - dbeierl@ibm.net