Date:         Thu, 13 Dec 2001 19:39:58 -0900
Reply-To:     Mike Moery <mike.moery@ACSALASKA.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Mike Moery <mike.moery@ACSALASKA.NET>
Subject:      Re: Battery Isolators vs. Relays
In-Reply-To:  <20011213180745.25034.qmail@earthlink.net>
Content-Type: text/plain; charset="iso-8859-1"

Why would you run the 'fridge on a battery anyway?  It works much better
on propane, and just takes a minute to light.  When I set up my
auxiliary battery circuit, the only part of the 'fridge I intend to
power is the little condenser fan behind it.  My primary objective in
adding an auxiliary battery is to operate the Eberspracher heater.  I
just need to figure out how to bypass the 10 minute timer on the heater
while camping, I'll have it licked.

    -Mike Moery
     Anchorage, AK
         ---------------
        ||E[__] [__]|[_]\ 
        | =======| -   ||   
 * * * *( o )-------( o )=  
 'Ol Bessie  '82TD Westy


-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf
Of Tim Hannink
Sent: Thursday, December 13, 2001 9:08 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Battery Isolators vs. Relays

The relay setup works great until the auxiliary battery develops an
internal short. The batteries attempt to equalize, but since the
internal resistance of one battery is zero, the other battery can only
get weaker. The alternator won't charge either battery since they are
connected in parallel when the engine is running. Eventually, both
batteries need to be replaced.

Why would the auxiliary battery short out? Since the refrigerator in the
Wolfsburg Camper model runs on only 110VAC and 12VDC, some people
(including me) tend to leave it plugged in while parked, totally
dis-charging the auxiliary battery. The fridge draws 8 amps/hour and
will discharge a new starting battery in 6-7 hours, the first time.
Every time the battery is deep discharged after that, you loose about
25% of its capacity. My 1 year old battery can run the fridge for a
little over an hour right now without the engine running. Eventually,
the battery will short out internally and not hold a charge.

The obvious solution is to install a deep-cycle battery in the auxiliary
battery position. My concern is having dissimilar battery types wired in
parallel and the effect it will have on the batteries. I will be
installing an isolator with the deep cycle battery(s) to keep this from
happening.

Another solution is to rotate the batteries every couple of months.

Or install all deep cycle batteries.

Tim Hannink
Goldibox - 1987 Vanagon Camper, Wolfsburg Edition
Winter Park, Florida
http://home.earthlink.net/~tjhannink/

--