"Doug" wrote:

Rather than use a combiner, my Ample Power regulator has provision to
drive a solenoid to parallel the start and house batteries when the
engine is running. My Xantrex 20 amp shore power charger drives both
banks when on shore power.

I have a pair of golf cart batteries for the house bank, and a normal
auto type for a start battery. All works well, and I find that the
start battery electrolyte rarely needs to be topped up. The house
battery needs topping up a couple of times a season.

A decent regulator or shore power charger will control the charging
voltage to keep the batteries from gassing. For example, when the
house battery is low, but the start battery is up (as is normally the
case), the charger might be putting out 14.4 volts or so. The house
battery will be taking 20 amps, while the fully charged start battery
is taking only few hundred milliamps. Eventually the charger will
switch to float mode, and the voltage will go to around 13.3 volts (or
whatever you have the Xantrex set for).

Charging batteries in parallel is not a problem if the batteries are
in good condition. The most deeply discharged battery will control the
charger's output - the other battery will be at the same voltage, but
since it fully charged, it's charging current will be less. There is
no reason why it should lose electrolyte faster than the other one.


I suggest you get rid of a deep cycle battery for the starting battery. Use
a regular starting battery, such as is available at any automotive supply
store. They are cheap and are designed for delivering a lot of current for a
short period of time in a starting application.
The combiner, if wired correctly, should be only charging the banks when the
alternator is delivering power. Shore power and the battery charger should
not be a part of the combiner path. They should be two separate, not
simultaneous, charging circuits.
Ensure only the engine is connected to the start battery. There should be no
additional loads on the start battery requiring it to be charged frequently.
Suggest you put a heavy duty ON/OFF switch in the path between the shore
power charger and the start battery. Turn ON only when you feel the starter
battery needs a charge.

Doug K7ABX


Larry Bradley VE3CRX
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