Date:         Mon, 23 Aug 2004 22:04:49 -0700
Reply-To:     Westyman <syncrowestytd@MINDSPRING.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Westyman <syncrowestytd@MINDSPRING.COM>
Subject:      Re: dual battery isolator
Comments: To: VWVANFULLTIMERS@yahoogroups.com
Comments: cc: Syncro list <syncro@yahoogroups.com>
In-Reply-To:  <a2dc60a2c41b.a2c41ba2dc60@optonline.net>
Content-Type: text/plain; charset="US-ASCII"

Dennis,

Thanks, good info to know. I really wasn't aware of the voltage drop issue,
among others. How do you feel about Hellroaring's isolator-combiners? they
claim less than .005 volt drop. http://hellroaring.com/bic75150.htm I really
don't see a relay system keeping proper charge on tow batteries so widely
different.

And yes, this is getting expensive just to keep food cool, but a cooler is
out of the question for the month-long trips I take, in both the constant
need for ice and space limitations.

Karl

-----Original Message-----

Although many folks have had success with conventional isolators, they are
overall a bad idea. Yes they can be more reliable than relays since they
avoid dirty or welded contacts, but they are inefficient. For starters,
after they get warm the actual voltage drop is closer to 1.1 volt. At 90
amps, the isolater is dissapating almost 100 watts. This is why they need
heat sinks. You are paying for this power. Now, with this voltage drop, you
are getting less than 13 volts to the batteries and accessories. Ok, so now
you can modify the regulator to increase the voltage or use a remote sense
wire to compensate. At full load the limiting factor of an alternators
capacity is its own resistance. Thus at full load, it is only slightly more
than 50% efficient. Yes, 1/2 the power produced is given off as heat in the
alternator itself. That is why they have a big fan and they still get hot.
So, we increase the voltage of the alternator by 1.1 volt so at 90 amps the
alternator dissipates an additi
onal 100 watts of heat. Can we say shorter life? So at full load, we are
wasting ~200 watts of power due to the use of the isolator. Under ideal
conditions, 1 HP = 746 watts. Not that you will notice but we are wasting
.26 HP here. The big issue here is the load on the alternator.

Dennis