If you read your link, Sean used a RELAY instead of an isolator with his
Optima dual battery setup. He also added an inverter. He first tried the
wimpy relay kit sold by TBD but switched to a REAL relay that costs
about $20 and can handle 100 amps.

http://www.vgonman.com/auxbat.htm

Mark

randy charrette wrote:

>I'm no electronics expert, so I found a web site (www.vgonman.com) and copied his set-up. It has worked great for about 3 years now. This is set-up with a isolater.
>Randy
>87'Syncro TIICO
>
>David Marshall <VANAGON@VOLKSWAGEN.ORG> wrote:
>
>I can't see an issue with a 70A relay load wise as your alternator is 90A
>and only on a good day. I use a generic Bosch 40A relay for my 2nd battery
>in my TriStar and I have never had an issue and I have a 120A alternator.
>Charging battery from a dead flat doesn't make the relay nor the 2x12ga wire
>running to the battery hot or even warm to the touch. I think the relay is
>the simplest and probably the most effective of designs. The diode
>isolators are not good in my opinion as they introduce a 0.7V loss in the
>system over both batteries. The computerized isolators that give the
>starting battery and deep cycle the voltage they want to see is the best
>bet, but expensive and really I think the deep cycle will charge fine on the
>relay with an alternator designed to charge a starting battery. 1000s of
>fishermen driving home charging their deep cycles on their F150 can't be
>that wrong.
>
>