Is there a charge light on the charger? Or a a FULLY Charged light?

If so, measure the voltage of the light. It will either be 110VAC or
maybe 12 or 24 VDC.

Go to Radio shack and buy a relay with that voltage as the excitation
voltage and can handle the load of the fan. Make sure the fan you buy is
ignition protected. (ALSO BUY A SOCKET... EASIER TO SOLDER AND REPLACE)

Mount the relay somewhere where the sparking will not blow you up (Gas
boat I assume??)

Most relays will have a normally closed, Normally open and common.
Depending on which light you have, select the proper terminals and
connect to your fan.


One other option.... You may take your voltmeter and follow the battery
leads into the charger and past the final diodes... These should read
+13V (or 26V) only during charging. You should be able to connect the
proper voltage fan to this. Some chargers are different but this would
work on my old charger.

BE CAREFUL... 110V is all around when the charger is plugged in or the
breaker is on. Also, 110V may be around when the charger is unplugged
or the breaker is off. (Capacitors store power)

You may find a relay that turns on between 24V and 26 V but it may
flutter at 25V and burn up the contacts.




CS wrote:

I want to fit a small fan to vent my battery box when the battery is
charging. I only want the fan to run during charging, so was thinking
of a relay that would only close when the voltage is above 28v or so.
Any ideas???