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I have the following:

  • Two 12 volt batteries hooked up in series to supply 24 volts to a
    a 120 watt LED lightbar.
  • One 12 volt battery that is hooked to a switch.
  • A relay that has a max operating voltage of 27 VDC. (http://www.foocles.com/FLS821G-pd934013.html)

Can I safely supply the relay with 12 volts to "switch on" the 24 volt load to power the LED lightbar?

Thanks.

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    \$\begingroup\$ The motor is an inductive load, and the relay only rates a resistive one. Can you provide information on the motor? The 27VDC rating is for the contact side, so voltage wise you are OK, but depends on how much current the motor draws, including inrush. The 12V will turn the relay "ON", the question should be if the contacts can handle the motor load. \$\endgroup\$ – Ron Beyer Nov 9 '17 at 19:55
  • \$\begingroup\$ @RonBeyer - added more detail, thanks. I should have worded more clearly. I shouldn't have even mentioned the motor, as it will not be connected to the relay. \$\endgroup\$ – dugas Nov 9 '17 at 19:57
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    \$\begingroup\$ The linked page indicates that the relay is available with either a 12 volt coil or a 24 volt coil. You will require the 12 volt version to operate it from 12 volts. \$\endgroup\$ – Peter Bennett Nov 9 '17 at 20:33
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Assuming that you are not controlling the trolling motor, this should work just fine (simplified of course, the LED in the diagram is the entire unit, including internal resistors or whatever circuitry allows it to run directly from 24VDC):

schematic

simulate this circuit – Schematic created using CircuitLab

The relay you linked is rated for up to 20 amps at 27VDC, which is quite a bit of current. The 12V side of the relay doesn't affect the 24V side of what you are switching. One is the coil rating, the other is the contact rating.

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