I have a small electromagnet which moves a lever (it's a part from a larger device). I'm not sure of the supply voltage but other parts of the device required 20V.

The resistance of the electromagnet is 53 ohms.

I tried low voltages and nothing happened, but the highest I can try at the moment, 12V, slightly moved the lever.

Is there a way to confirm the voltage required? If it is 20V, will a resistor be needed?


  • \$\begingroup\$ Have you read the datasheet? That should tell you what voltage is needed. \$\endgroup\$ – Puffafish Aug 21 '18 at 12:13
  • \$\begingroup\$ If you do add a resistor, it will just drop the voltage down again. So you probably don't need one. There's no magic way to tell what voltage the electromagnet is designed to run at. Just watch you don't let it overheat from running too long. \$\endgroup\$ – Simon B Aug 21 '18 at 12:17
  • \$\begingroup\$ Dump the electro-magnet and buy one with a spec. \$\endgroup\$ – Leon Heller Aug 21 '18 at 12:19
  • \$\begingroup\$ Careful study of the "larger device" should tell you what is required. \$\endgroup\$ – Charles Cowie Aug 21 '18 at 12:27
  • \$\begingroup\$ @Puffafish Unfortunately I don't have a datasheet and there's no markings on the electromagnet. \$\endgroup\$ – user2878409 Aug 21 '18 at 12:55

The resistance of the electromagnet is 53 ohms.

With that information we can, at least, calculate the power dissipated in the coil.

$$ P = \frac {V^2}{R} $$

Note that the square term means the power will rise exponentially with voltage.

  • At 10 V \$ P = \frac {V^2}{R} = \frac {10^2}{53} = 1.8 \ \text W \$.
  • At 20 V \$ P = \frac {V^2}{R} = \frac {20^2}{53} = 7.5 \ \text W \$.

It may help to try and think of this in terms of something you are familiar with - say a 6 W car tail light. Can you imagine holding your hand on the powered lamp? What temperature rise would that much heat cause in your electromagnet?

I would be inclined to test it carefully and see if you can hold your hand on it gradually increasing the voltage, if possible.

If you are going to damage it then heat will be the cause.


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