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Rapidly change electro magnet polarity.

Discussion in 'General Electronics Discussion' started by Bob Cash, Oct 11, 2017.

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  1. Bob Cash

    Bob Cash

    Oct 11, 2017
    I have tried to get assistance in the past but, due to my total lack of expertise, have had no success.
    I wish to purchase a device which will simultaneously change the polarity of two electro magnets between once and a few hundred times a second.
    H bridges and signal generators have been mentioned but mean nothing to me really. I need to know where I can get one of the shelf.
    When posting before, I get asked questions like power, et cetera, which I cannot answer. All I can say, at this stage, power and size are not too important. I expect magnets to be rectangular and about two inches long. As long as they have reasonable power, that would be sufficient.
  2. duke37


    Jan 9, 2011
    A two pole changeover relay wil give the action you want but may not work at a few hundred times a second and if it does work is likely to wear out quickly.

    The magnets will have an inductance, possibly large. Perhaps laminated pole pieces would be best.

    An H bridge is the alternative, it will act much faster and will not wear out.
    You will need to know the power to specify voltage and current. You will not need to specify magnetic force.

    There are many H bridges on e-bay at very reasonable cost.
  3. BobK


    Jan 5, 2010
    You can change the polarity of the driving voltage quickly with an H-bridge, but the magnetic field will not change polarity fast because of the effect of inductance. Do you have the facility to measure the inductance of the your electromagnet?

    At 1 Henry with 1 Amp, it would take 200V to change the polarity 100 times per second.

    duke37 likes this.
  4. davenn

    davenn Moderator

    Sep 5, 2009
    the suggestions berkeman gave you on the Physics Forums was spot on
    you need to follow up on that advice instead of posting everywhere else on the net

    you will have to make your own electromagnets as they are not something you can readily buy

    and you never did answer him as to what this project was all about ???
  5. Minder


    Apr 24, 2015
    What sort of magnetic effect are you hoping for switching that fast?
  6. Bluejets


    Oct 5, 2014
    Strap a bar magnet onto the end of a dc motor and vary the speed ?
  7. Alec_t


    Jul 7, 2015
    What force do they need to exert, at what distance, to qualify as 'reasonable'?
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