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Switching Polarity of Electro-magnet.

Discussion in 'Power Electronics' started by jeremiah25, Sep 6, 2018.

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  1. jeremiah25


    Sep 6, 2018
    I am not trained in electrical or electronics theory; and wish to construct an electronic switch capable of facilitating an alternation in polarity in an electromagnet [EM] continually powered by a DC battery source. Using mediating terminals, my idea is to incorporate transistor switches in 2 circuits to the electromagnet, one circuit with wires [+] and [-] to ends [A] and of the EM, the other with those [+] and [-] wires to ends and [A] respectively; and to switch one on simultaneously with switching the other off and vice versa.

    The problem is that because the resistance in the EM coil is ~0.1 Ohm, and the current is ~120 Amps --necessary for EM strength--, I don't know what sort of transistors to use, or whether any transistor is capable of handing the power involved. I wondered therefore whether some timing device used in high power transmission might be suitable.
  2. Alec_t


    Jul 7, 2015
    Welcome to EP!
    What you are looking for is called an H-bridge, which uses four semiconductor switches. Power MOSFETs and IGBTs are available which can handle 120A, but great care is needed in controlling them to avoid them frying, especially if rapid reversal of the current is wanted.
    Why do you want to reverse the magnet current?
    jeremiah25 and abeluna like this.


    May 20, 2017
    Yes it would be possible using some high current MOSFET's in an "H" bridge format. With some suitable logic, it could become a single switch operation.
    jeremiah25 and abeluna like this.
  4. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    This better not be about building yet another zero-point free-energy thingamabob... what is @jeremiah25 trying to DO with his electromagnet? Do we need to wear tin-foil hats while it is running? Chain-mail Faraday shielding suits? Or is this simply the probe coil for a very deep metal detection scheme? Please answer @Alec_t's question:
    davenn and abeluna like this.
  5. Nanren888


    Nov 8, 2015
    Just to add yet another, associated, question: How often do you want to alternate/switch it?
    Once a day, once a second, thousand times a second?
    What frequency are you looking for?
    Colis, which means Inductive loads, mean spikes and phase shifts between voltage and current. This can cause issues for switching.
  6. davenn

    davenn Moderator

    Sep 5, 2009
    @jeremiah25 PM me with what you are trying to achieve

    Till I get a response, the thread is closed

    Edit: reporting this post is not a response (it was not understandable and we can't reply). Send a PM to a moderator.
    Last edited by a moderator: Sep 7, 2018
    jeremiah25 and hevans1944 like this.
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