I am by no mean an electrical guru, but, might diodes work in this
situation?  My understanding is they are one way streets for current.  Seems
they would keep the charging from the alt. from getting back up the line to
the solar and smart charger.  Also, you could hard wire everything in to a
selector switch, possibly a headlight-type, three way switch.  OFF-no aux
charging reaching the battery (only alt;) Position 1-Solar Charging;
Position 2-Smart Charger.  Let us know what works out.

Brendan Slevin
84 GL Totoro
I have measured out my life with coffee spoons. -T.S. Eliot

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of
Loren Busch
Sent: Wednesday, July 18, 2007 9:52 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Aux Battery Charging Alternatives Question for the Electrical Gurus

Right now I have wiring in place for three ways to charge my aux battery.
First, and permanently connected, is the alternator when engine is running.
The next two are wired right now so that only one can be connected at a
time: Solar charge controller (and solar panel) and an onboard 30 amp
'smart' charger.
Question:  What kind of problems, if any, would I encounter if all three
were connected to the battery at the same time?  Assuming that only one
would ever be running at any time, would I expect problems such as the solar
controller seeing the voltage from the 110v ac charger and causing damage?
Or the solar controller seeing the voltage from the alternator and having
problems?  Or any other combination that should be avoided?  Just to be
careful I'm now set up so that the solar and the 110v ac charger can't be
connected to the battery at the same time but the ideal system would be to
have them permanently wired in.