Boat Forum / Electronics / April 2007

Connect all (-) negative grounds together.  Use battery cables to
connect the (+)  positive battery  terminals directly to the big
contacts marked 1 and 2 on the switch. Wire the output (the remaining
big terminal ) to the engine where the single battery was connected.
There are, or should be, 2 other small terminals on the switch.  They
are used to interrupt the field fire which controlles the alternator
output voltage and current.  The field  switch will disable the
alternator when (before, actually) the battery switch is set to off,
protecting the alternator from internal high voltage which is
generated should a battery be not properly attached.

I would install the batteries (+) terminals last to prevent accidental
shorts while wiring batteries.  One instantaneous wrong connection can
be disasterous.

I would check before installing that the field circuit opens before
the battery terminals do.  Some switches, it is said, do not.

Welcome to the arguement concerning equalisation of batteries while in
the "both" position. You will want a hydrometer and a supply of
distilled water. Use only steam distilled water to replenish the
batteries.

You will probably want to wire bilge pumps directly to a battery (+),
so that the pumps still work when ships power is turned off.

If you are nervous, you should be.  If you are not qualified, hire a
skilled worker. Explosion and fire is a constant hazard when working
with storage batteries.

Terry K

I assume you are after an engine battery and house battery.  Connect
both batt negatives to common ground.  Connect domestic battery pos to
a on off batt switch - do not bother with a 1 2 all switch.  Connect
dom bat pos to eng bat pos via a relay - Curtis/Albright - controlled
by something like a Smartbank - www.smartgauge .co.uk  Connect
alternator pos to domestic batt pos or batt side of batt switch -
replace weedy std alt wiring with something more beefy.  Can leave alt
neg connected to common ground.  Have a suitable feed from live side
of batt switch to supply "always on" items - bilge pump, alarm etc
etc.
Smartbank will control when relay operates - charging engine battery
when engine is running and then disconnecting engine battery.  Smart
bank can also be used to parallel batteries for emergency starting
using RJ45 cable and push switch.