It's a long swim!
back to shore with starting power confidence!
Many boats are equipped with dual batteries and a
heavy duty switch with an OFF, 1, both, 2 position. So that
maximum cranking power is achieved, an operator may set the switch to
"both" just before starting. After starting, the switch is left
on "both" so that charging both batteries is achieved. But
upon arrival at the desired location, the engine is turned off, leaving
the operator to "remember" to switch the battery from
the "both position". It is very easy to forget this step
and consequently run down both batteries. This can leave
you in a dangerous situation! ( i.e. without power to
operate your boat or your electronics.) There are many many ways
to prevent this (all with their own pros and cons.) The
discussion below covers some of the best ways to keep your batteries
isolated and prevent this "hell of a situation"
One of the first options one normally considers is the
basic diode isolator. But the diode isolator has an
inherent voltage drop of about 0.7 volts even at low
currents. This loss of voltage tends to result in
undercharged batteries. Batteries left in undercharged
conditions for extended periods will loose capacity and its life will
be substantially reduced. With diode
isolators, all of the alternator current must flow
through the device resulting in maximum heat generation.
Therefore, for high current alternators, the diode isolator requires
very large heat sinks. This is not so with the Hellroaring battery
isolator / combiners. They can be set up so that the majority of
the alternator current bypasses the isolation device. We
recommend that you do not use plain diode isolators.
Combining batteries during charge eliminates this
chronic undercharge condition. Of course, you could
combine them manually during charge by switching a relay.
However, this still requires that you to remember to switch at the
proper time. Or you could wire a relay to your
ignition switch, but this will only give you a false sense of
security. If your alternator quits, you will still
run down both batteries! This
is a time when you need your backup battery the most!
We recommend an automatic combiner as the better
solution. But, since mechanical relays/solenoids have their
own problems such as sticking contacts, arcing and contact wear, we
recommend our solid state automatic battery isolator/combiner
as the best solution.