Marine Application Notes:
|Sometimes, It's a long swim!
|Get back to shore with starting power
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.