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Simplest circuit to drive a 24V DC motor from the mains?

Discussion in 'Electronic Basics' started by Foo, Sep 16, 2009.

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  1. Foo

    Foo Guest

    Hi, let's say that I have this hypothetical motor that is rated for
    24V DC and draws an unknown amount of current (say around 1A).

    Input is 230V AC.

    I'm wondering if the motor will work properly with a step-down transformer
    to 24V AC and a rectifier but no smoothing.

    Is that going to make it noisy or break it in the long run?

    Thanks.
     
  2. Rich Grise

    Rich Grise Guest

    No, as long as the output of the rectifier is 24VRMS. It might have a
    bit of 120HZ hum (I'm assuming a full-wave rectifier), but the motor
    itself has a lot of inductance, which sort of makes it its own filter.

    Hope This Helps!
    Rich
     
  3. Foo

    Foo Guest

    Yes, thanks!
     
  4. Jamie

    Jamie Guest

    If its just a commutated brush type motor, it should work fine.
     
  5. Beware. The operational current to drive a 24V/24W motor wil be about 1A as
    you might expect. The inrush current however will be a multiple of that 1A
    and your rectifier should be able to handle that current. A 10A full bridge
    rectifier is no overkill.

    petrus bitbyter
     
  6. Foo

    Foo Guest

    Unfortunately, I don't think this motor can be replaced.

    I didn't include this in my first post, but was actually thinking
    about such a transformer _and_ a four diodes bridge to allow reverse
    operation of the motor with a two-way switch.
    Thanks for the tip. Maybe a fuse on the 230V side is a good idea too?
     
  7. Rich Grise

    Rich Grise Guest

    Yes, but size it such that it won't blow unless there's a transformer
    failure. IOW, the fuse on the motor side should blow first.

    Hope This Helps!
    Rich
     
  8. Rich Grise

    Rich Grise Guest

    Also, that's what "Slo-blo" fuses are for.

    Cheers!
    Rich
     
  9. Foo

    Foo Guest

    Thanks for your replies.

    Now, if I happen to add a capacitor to smooth the DC output somewhat, do I
    need to replace my transformer with one that outputs 18V instead, or will the
    voltage drop take care of that?

    Which setup would you recommend? My goal is to keep this circuit as simple
    and efficient as possible. I'm willing to add a capacitor if it improves
    efficiency.
     
  10. Foo

    Foo Guest

    Okay. One last question: for a 25W motor, is a 30VA transformer appropriately
    sized?
     
  11. Rich Grise

    Rich Grise Guest

    Yes, with the full-wave bridge and NO capacitor.

    Cheers!
    Rich
     
  12. Foo

    Foo Guest

    Thanks!
     
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