Refueler
Well-Known Member
I have a cool-box that eats batterys. Well which don't ? apart from Waeco compressor jobs. But they are significantly more expensive.
My Cool-box is large, came with the boat and well insulated. I checked with digital thermometer it's working and it dropped internal temp to ~ +3C when outside was over 16C. But it ate 7A steady doing it.
So 12V 30A relay in hand - I wanted to connect so only power when engine on and alternator run up and charging. I bench checked relay and found it didn't have diode as seller reckoned. It worked both ways round with connections.
Oh Dear ... what to do .. OK - lets try it.
Down to boat and wire in parrelel to charge light .. Click. Change wires over ... Click. That's no good. (engine off)
Arrrrrr let's try a different point to connect ... AFTER the light. No click. Meter shows 3.4V .... interesting as 12v feed to light ... through to alternator field coils. So ok start engine ... WOW meter jumped to 13.5V with intermittent 15V ... CLICK - relay operated.
BINGO !! So connecting after the light and relay works as desired. Now Cool-box will only come on when alternator is charging system, saving batterys !
Next is to connect in a 1-off-2 switch so that I can choose between mains supplied 12v or the relay.
But I've come away confused as to why it shows such low volts after light for coil exciting ... I understand the alternator back-feeding 13.5+V ...
Anyway - cold beers now !
My Cool-box is large, came with the boat and well insulated. I checked with digital thermometer it's working and it dropped internal temp to ~ +3C when outside was over 16C. But it ate 7A steady doing it.
So 12V 30A relay in hand - I wanted to connect so only power when engine on and alternator run up and charging. I bench checked relay and found it didn't have diode as seller reckoned. It worked both ways round with connections.
Oh Dear ... what to do .. OK - lets try it.
Down to boat and wire in parrelel to charge light .. Click. Change wires over ... Click. That's no good. (engine off)
Arrrrrr let's try a different point to connect ... AFTER the light. No click. Meter shows 3.4V .... interesting as 12v feed to light ... through to alternator field coils. So ok start engine ... WOW meter jumped to 13.5V with intermittent 15V ... CLICK - relay operated.
BINGO !! So connecting after the light and relay works as desired. Now Cool-box will only come on when alternator is charging system, saving batterys !
Next is to connect in a 1-off-2 switch so that I can choose between mains supplied 12v or the relay.
But I've come away confused as to why it shows such low volts after light for coil exciting ... I understand the alternator back-feeding 13.5+V ...
Anyway - cold beers now !
