I am trying to figure out how an AC solenoid coil maintains its N and S magnetic polarity.

Since in a sinusoidal AC, current alternates in both directions. How does the solenoid not change polarity (N and S) for each half-cycle?

I would really appreciate it if someone would explain this to me.

  • \$\begingroup\$ Do you think it is worth accepting the answer? \$\endgroup\$
    – Solar Mike
    Commented Mar 27, 2023 at 19:13

1 Answer 1


An AC solenoid's coil does change magnetic polarity in each cycle, but because the moving bolt is not a magnet but plain iron or steel, both magnetic polarities will pull the bolt in, so no problem there.

There is another problem to be solved though, and that is that the AC current has zero-crossings, and the current through the coil can go to zero. This can make the solenoid vibrate a little and cause uneven power and wear. You can read about this and the solution in this article (no affiliation).

  • 1
    \$\begingroup\$ That makes so much sense, I didn't think about that. Thank you very much \$\endgroup\$
    – rthony
    Commented Aug 10, 2022 at 8:44

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