Dry Contact Rating & application

ramarama Solar Expert Posts: 36
A dry contact rating of 50VDC, 3A -- does this mean this relay can only be used to switch on/off small DC loads that are no more than 150w?
I'm confused as to suppose I have a 1kw generator, does this mean there is no way this dry contact can be used to switch the genset? But then the 1kw is the output rating, whereas the dry contact is used to switch only the power circuit of the generator. Would the power circuit of the generator be listed as a different specification that I need to look for, or am I just thinking this whole thing wrong? :confused:
Appreciated if anyone could point me in the right direction.


  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: Dry Contact Rating & application

    You've got it right.

    That 50 vdc, 3a dry contact is only big enough to drive another larger contact relay. A dry contact that size can also control a few very small loads (ie, LED indicator light, battery enclosure vent fan, LED room light).

    If you want to use it for a generator's 12v, 2 wire start circuit you need to make sure that the circuit's current is less than contact's rating. I would venture to say that most generator's 2 wire start contacts are low amperage but there are exceptions.

    If you don't have any luck looking up the specs in the manual you can easily check even without a good quality amp meter that can accurately record peaks. Get an in-line fuse holder with an "expendable" 2amp fuse and put the wires on the 2 wire start contacts.

    If the gen starts and the fuse does not blow, instal it in the circuit.

    If the fuse blows, get an automotive 12v, 30a contactor.

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Dry Contact Rating & application

    A 50 Volt 3 Amp contact rating means the Voltage can be no more than 50 and the current can be no more than 3. This is not the same as "150 Watts". For example, that Wattage could be 150 Volts @ 1 Amp. The Voltage would then be too high for the contacts to safely interrupt and they might arc. Conversely, it could be 150 Amps @ 1 Volt in which case the current flow through the contacts while closed could weld them shut or melt them altogether.

    Just clarifying for anyone who doesn't understand the difference.
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