RE: [A/S] Intellipower hookup question

["DT/BW" <dtbw_1999@xxxxxxxxx>]

David,
What you are wanting is known as battery isolation.  The goal is to make
sure that the trailer does NOT pull power from the tow vehicle UNLESS the
engine is running (ie alternator power is available.) 

There are several different approaches.  You want to make sure that what
ever you install is adequately fused and can handle the max current that
your alternator can output.  Typically the chargeline wiring to the trailer
limits the current to the 30-40 amp range, but that is totally dependent on
the wiring (chargeline AND Negative).  It is safer to assume 100amp and fuse
to 50amps. 

The simplest, but usually the least long-term reliable is a high-current
electromechanical relay that is engaged by the accessory circuit on your tow
vehicle (the thought being that the engine is usually running when the
accessory circuit is hot).  The relay connects the trailer battery, thru a
fuse, to the alternator/battery on the tow vehicle. The downside of this
approach is that due to the potential high currents that are switched, the
contacts in the relay tend to fail, leaving you without ANY ability to
charge the trailer battery.   

The alternative is electronic switching.  Even the lower cost units are
reliable but most of these designs have the disadvantage that they exhibit a
voltage drop of over 1volt which limits the charging capability to the
trailer.  There are other electronic designs that overcome this problem and
exhibit only a few thousandths of volt of drop.  At least one of the better
designs (www.hellroaring.com) has the ability to remotely control the unit
(ie NO-connection between trailer battery and tow vehicle, one-way power
xfer when engine is running, & finally, full two way transfer regardless of
engine status).  The advantage of being able to switch to full 2-way xfer is
that should you have an alternator failure, you can use the trailer battery
as well as the tow vehicle battery to continue power the engine as you try
to make it to the next town.  With modern engines, NO battery power = NO
engine due to the electronics.  Another use of the 2-way xfer is that allows
the convertor in the A/S to also charge the tow vehicle when stopped, plus
allowing my solar panels on the A/S to charge both batteries.  On sunny
days, I also tow with the Hellroaring set to OFF (allowing the solar panels
to charge the trailer batteries).  This takes a bit of load OFF the tow
vehicle (ie running the alternator at higher output)

The Hellroaring unit is not cheap (about $200 with remote control), but it
is solidly engineered (I am a EE, so I have some expertise on such matters)

David