pracTical
exceed a ratio of 4:1, or a larger output
alternator has been fitted, a dual-output
charge controller, diode charge splitter
(above) or Voltage Sensitive Relay (VSR)
should be installed to prevent the start
battery becoming overcharged.
A simple 1-into-2, diode-type circuit
splitter allows the charge from the
alternator +ve to feed into more than
one battery, but isolates them from
each other once charging has ceased to
prevent current flowing between them.
Unfortunately the diodes also act as small
resistors, cutting the charge voltage down
by between 0.4-1.0V, although this is not
usually a problem with a smart regulator
batteries, then the regulator might well voltage to around 16V. This feature is as, being battery sensed, it should
never reach the second or third stages automatic once selected and is used to automatically compensate.
before the engine is switched off. If this dissolve the sulphates that build up on You can incorporate a VSR instead of
is the case, you may as well fit a single- the plates over time, limiting the charge a diode splitter, whereby all the charge
stage, high output regulator. In effect, capacity and overall life of the battery. initially goes to the start battery until it
these are really two-stage devices because However, if this is used, you will need reaches a voltage of around 13.8V, after
they keep the charge high until the battery to disconnect the main supply to any
reaches its optimum voltage and then sensitive electronic equipment, so it is
gradually reduce the charge current to unlikely you’d use this feature underway.
stop the battery gassing or overheating,
Tip
switching back to high again if a heavy
load is put on the batteries.
Multiple
Some claim to be 4-stage regulators,
but usually the 4th stage is actually the
battery banks
same float mode as in stage 3, but able to Engine start batteries are easily recharged
instantly return to stage 1 when a heavy over a short period, whereas deep-cycle
load is switched on – more of a standby, service batteries need more charge current
or power supply mode really. over a longer time. The variation between
Some smart regulators also have an the two is often overlooked, but if the
‘equalise’ mode, which boosts the charge difference between their total capacities
I
t is usually only one or two power-hungry
electrical items on board that drain your
power reserves dramatically, often a fridge
or heavy-duty water pump. VSRs are not
only to be used for battery isolation, but can
also be incorporated in these supply circuit
as a low-voltage protection device. LVSRs
will sense when the voltage drops below
11.0V and automatically shut the device
down until the voltage rises again. Installed
into non-essential circuit such as the fridge
etc, this could save you losing the more
vital equipment such as instruments or
chart plotter when you need them most.
An audible alarm in the circuit will also
give you a warning of the problem when it
first occurs.
118 Sailing Today September 09
ST149 Practical_Electrics
RTG.in116 116 17/7/09 15:22:49
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