wiring a voltmeter to the 2nd battery

blackberg

Seaman
Joined
Jan 1, 2011
Messages
66
I have two batteries on a switch, the second one will be for the trolling motor and backup starting.

I know I can run a wire from the positive to the ignition input, and the negative to the ground input on the gauge, but this will drain the battery, (slowly), since it would always be on. Any way around this easily? i was thinking of a relay actually but not 100% sure on how to wire it and partnumbers

-bb
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: wiring a voltmeter to the 2nd battery

If you have two batteries on a switch so you can start off either battery then if you want to know the voltage on the other battery just turn the switch to that battery. Turn the key on and read your voltmeter.
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: wiring a voltmeter to the 2nd battery

You can wire a second voltmeter directly to the second battery, bypassing the switch. If you want master ignition to turn off the meter, you need a light duty relay in the circuit, with the coil of the relay being driven by the ignition auxiliary or ignition circuit.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: wiring a voltmeter to the 2nd battery

Why complicate this with a relay? A simple three position - center off switch is all that's needed. Here is how. Center position is off. Up and down read the individual batteries. The voltmeter draws so little current the switch could be left on for a very long time before significant discharge occurs.

Onevoltmeter-twobatteries.jpg
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: wiring a voltmeter to the 2nd battery

The relay would be if he wants 2 meters at the same time, that's why.
 
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