Battery Isolators are generally known as sold state devices, (diodes),
that allow current to flow from the alternator to multiple batteries,
but prevent current from flowing from one battery to another. Any type
of switch or relay can also be used for isolation but the term has stuck
to the solid state devices. As far as I'm concerned, with the exception
of very high quality units such as the Hellroaring devices, these things
suck and in the RV world they are only used on low end units.

A "combiner" is really a control strategy. Either solid state or relays
can be used. Combiners are usually voltage operated and they have a
number of advantages. I have recently described the operation to the
list. Basically, if either bank of batteries is getting charged, the
combiner will connect the other bank. After charging, the banks will
remain connected until the voltage drops below some preset level,
(~12-12.5 volts), allowing both banks to provide power and then drop out
while the chassis battery is still at 70% or higher. This set up allows
a charger connected to the house batteries to also charge the main
battery.

Dennis

-----Original Message-----
From: VWVANFULLTIMERS@yahoogroups.com
[mailto:VWVANFULLTIMERS@yahoogroups.com] On Behalf Of edwardduntz
Sent: Thursday, May 05, 2005 7:47 PM
To: VWVANFULLTIMERS@yahoogroups.com
Subject: [VWVANFULLTIMERS] More charging system comments

Several people have posed some good questions and some good answers,
and I'd like to add a little more info and ask that Dennis Haynes
try to clarify something as well.

First, as to Joe F.'s question about the difference between
isolators and combiners- although their names would seem to indicate
otherwise, from what I have learned on the manufacturers' websites,
here is the difference: an isolator is to electricity what I check
valve is for water. It prevents "backflow" from a charged battery to
a discharged battery. A combiner goes a step further and prioritizes
the charging. For example, if you have a starting battery and an
auziliary battery, and they are both somewhat discharged, the
combiner will send all the current to the starting battery, and then
when that reaches a pre-set voltage, the auxiliary battery will be
charged.

Someone mentioned that they will be using an isolator or combiner to
facilitate better charging, which they hope will be better than the
stock relay. Dennis commented that the stock alternator setup will
not allow maximum charging, but, Dennis, please clarify here- no
matter what relay or isolator is used, you can't pull more current
than the alternator can produce. You might be able to prioritize and
route the current so that one battery does not drain another, but,
short of a more powerful alternator, there is no net gain with one
relay/isolator over another, correct? Dennis, please chime in here
to clarify.

Ed

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