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Chapter 4
VSR (VOLTAGE SENSITIVE RELAY)
Located on the battery
management panel
above and below the
battery switches are 2
VSR’s (voltage sensi-
tive relays).
The purpose of the
VSR is to protect the
engine batteries from
being discharged. Also,
when the engine batteries are fully charged it sends current
to charge the house battery.
When the cranking battery(ies) rise above 13.7 volts DC
the VSR switches to charge (cranking and house) both bat-
teries in parallel simultaneously. When the battery voltage
drops to 12.8 volts DC the VSR disengages.
This VSR capability is referred to as “dual sense”. This
permits the VSR to sense the voltage of both batteries
that it is connected between. If one of the batteries is
receiving a charge the VSR will close by paralleling both
battery banks to charge the house battery along with the
2 engine cranking batteries.
Notice the illustration shows a LED light which indicates
when lite that the VSR is closed and is sending a charging
current to a battery(ies).
If the VCR senses the engine batteries are being discharged
at a fast rate it will open and will not allow those batteries
to be overly discharged to the point that the engines will
not crank over.
An example of the above situation would be if the vessel
was stationary at sea for an extended period with various
electronic and entertainment equipment energized along
with the engines and
generator off the batteries would
normally discharge.
POSSIBLE PROBLEMS/SOLUTIONS (VSR)
1. Red LED light not visible at VSR-
One cause could be the remote battery
switch is not energized.
2. Red LED light stays on after the
engine is turned off- This is a normal
condition. The residual battery voltage because of bat-
tery charging has not yet dropped below 12.8 volts for
the VSR to cut out.
Red LED light
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