Courtney,
(sorry about the delay in my reply, I originally was reading it withthe cat in
my lap and he gets in the way of my typing)

Your "solenoid isolator" sounds like a heavier version of my relay.Here's my
understanding of isolators:

You don't necessarily want your trailer battery simply paralleled withthe
vehicle battery because it'd be possible to run down the latter tothe point of
"no start". That was the idea of the low-voltage cutoff that was originallyin
my A/S. Sooo....

They have come up with isolators. An electromechanical relay like mineor yours
is basically a heavy-duty switch that's operated by an electromagnetthat gets
its power from the ACC circuit in your vehicle. Turn the key on, therelay
closes, paralleling the batteries with no voltage drop. Disadvantagesare: the
coil draws some current, maybe as much as one amp. The batteries areparalleled
before the engine is started, potentially loading the vehicle batteryjust when
you don't need it. Main advantages are that a relay is cheap, rugged,and has
essentially no voltage drop.

OTOH: a diode isolator has no current draw from the coil, but will probablyhave
a bit of voltage drop. Silicon diodes or transistors will generallyhave about
2/10 volts of drop, so the trailer battery might not charge quite asfast or as
fully as with a relay isolator.

Probably more important than the style of isolator is to have heavyenough cable
going to the trailer. If I planned on mostly charging the trailer batteryfrom
the vehicle, I'd wire a totally seperate circuit from the normal 7-pin
connector, using #4 welding cable, a connector like they use on electric
forklifts, and #4 cable to the trailer battery(s). I'd connect thefeed directly
to the alternator output terminal through a large relay like yours.If the coil
is powered by the ACC circuit, it'll parallel the batteries only momentarily
while turning the key to the Start position, as the ACC circuit isdisabled at
that time. If the trailer batteries were totally flat, I'd try to rememberto
pull the plug at the bumper before starting. Or install a bypass switchso the
relay doesn't come in until I want it to. In any event, that lead needsto have
a fuse or circuit breaker in it, as a short to ground would be a veryserious
proposition indeed. A battery will produce WELDING current and cancause a
serious fire. (I saw a car burn up because a too-tall battery was installedand
it hit the hood)

Tom mentioned running #4 wire to the trailer connector, but he didn'ttell us
how he's going to get it into the terminals. <<grin>. Also, thatconnector won't
handle the high currents that we're talking about; a pair of 105-ampbatteries
will draw a BUNCH of charging current for quite a while if they'rerun down a
ways. That's why I'd use the forklift-style connector.
 

<<JIm>>

Courtney Gwyn wrote:

> Thanks for your reply, I too run dual Optimas in my Sub, with a Wrangler170
> amp alternator and solenoid isolator. It's my understanding thatif you
> connect to the alternator you are effectively connecting to yourmain
> battery, as they are hardwired together and not separated by theisolator.

[[clip]]

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