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Is there any method or formula that can be used to find the operating voltage of a coil using the resistance of the coil? If so, is it also applicable to AC coils or any other technique?

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  • $\begingroup$ Are you given the current I aswell ? If so you can just use V = IR $\endgroup$
    – Dan Khan
    Dec 18 '18 at 17:53
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Most relay coils carry a specification on how much current must be applied in order to pull in the contacts. Knowing this and the coil resistance, ohm's law then tells you what voltage will be necessary.

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  • $\begingroup$ Thanks brother for your answer but i need how can i know about the operating voltage of af a contactoror relay coil by the value of resistance $\endgroup$ Dec 19 '18 at 15:20
  • $\begingroup$ does the relay have a nameplate on it with its specifications printed on it? $\endgroup$ Dec 19 '18 at 18:50
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    $\begingroup$ You can't know, brother, because the pull in requires a certain amount of power to overcome spring resistance. Resistance alone isn't enough to work this out. The details will be on the relay datasheet. $\endgroup$
    – Transistor
    Sep 14 '19 at 21:44
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You cannot determine the operating voltage of a coil in this way unfortunately.

The simplest way I can think of to determine the voltage of an unmarked relay would be to connect it to and adjustable power supply (if DC) or variac (if AC). Then simple turn up the voltage until the relay seems to "click" reliably. I would then turn it up a bit more to provide an operating margin.

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