Jim, I love it.. a silicone diode has .5 volt drop across it. they useto recommend
that you step up the atlernator to make up for the 1/2 volt drop. Thenthey out the
regularors on the inside of the alternators and unless you were Mandrakethe
magician you were stuck with whatever the damn alternator put out.The relay dosn't
have a voltage drop accros it unless it is defective. The trick isto control when
it goes on and off. Jim's Acc control is a good choice as the relayis moot until
the ACC line is energized which makes it possible to borrow energyfrom the trailer
battery if you need help starting the tow vehicle. incidently any wirebigger that #
8 becomes a serious problem as far as phisicaly fitting things together.I do
trolling motors and bought a $275 tool just to crimp #8 and # 6 electrical
connectors. It is not as complicated as it sounds and the addage I'vealways had is
the simpler the better. Works for trout too.
Dave/ from Pepperell

Jim Dunmyer wrote:

> 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 paralleledwith the
> 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 wasoriginally in
> my A/S. Sooo....
>
> They have come up with isolators. An electromechanical relay likemine or 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,the relay
> closes, paralleling the batteries with no voltage drop. Disadvantagesare: the
> coil draws some current, maybe as much as one amp. The batteriesare paralleled
> 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 willprobably have
> a bit of voltage drop. Silicon diodes or transistors will generallyhave about
> 2/10 volts of drop, so the trailer battery might not charge quiteas fast 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 trailerbattery from
> the vehicle, I'd wire a totally seperate circuit from the normal7-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 onlymomentarily
> 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 toremember to
> pull the plug at the bumper before starting. Or install a bypassswitch so the
> relay doesn't come in until I want it to. In any event, that leadneeds to have
> a fuse or circuit breaker in it, as a short to ground would be avery serious
> proposition indeed. A battery will produce WELDING current and cancause a
> serious fire. (I saw a car burn up because a too-tall battery wasinstalled and
> 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,that connector 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 aWrangler 170
> > 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]]
>
> --
>
> <<http://www.oldengine.org/members/jdunmyer>>
> <<jdunmyer@toltbbs.com>>
> <<lower SE Michigan, USA>>
> <<mailto:jdunmyer@toltbbs.com>>