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Speed control of AC motor — Parallax Forums

Speed control of AC motor

agfaagfa Posts: 295
edited 2008-05-26 17:08 in BASIC Stamp
Is there a practical way to control the speed of an AC motor?· Example: A 120V single phase, single speed motor, such as one found on a table saw or router.· Could this be accomplished by varying the supply voltage, or the frequency?


Also What determines the direction of the motor?

Post Edited (agfa) : 5/26/2008 1:02:59 PM GMT

Comments

  • RickHRickH Posts: 40
    edited 2008-05-26 13:32
    Yes you can do it with a properly tuned Tank circuit and PWM on some IGBT's or SSR's. I recommend purchasing an equally rated VFD for this job if you have never done it though. most are 0-10 V controlled and quite easy to integrate into a stamp.

    VFD's are simply an AC rectifier to turn AC to DC - PWM control over the DC line - Tank circuit (Includes Inductance from motor in calculations) to smooth out the DC Pulse. This is not a simple circuit and it has quite a bit of power. Very dangerous to work with for even an intermediate EE. I would recommend buying one and skip making it if you are not familiar with them. I am assuming this as you had to ask how to do this.
  • agfaagfa Posts: 295
    edited 2008-05-26 14:04
    Thanks for the reply.· I am familiar with 3 phase output VFDs, I didn't realize that there were single phase output versions, or that a single phase motor could be driven from a 3 phase vfd.· I will do some searches regarding this.

    Also, I may need some clarification, I thought PWM refered to a DC duty cycle.· The VFDs I'm familiar with, if I understand correctly, output AC.


    Post Edited (agfa) : 5/26/2008 2:09:18 PM GMT
  • stamptrolstamptrol Posts: 1,731
    edited 2008-05-26 17:08
    agfa,

    Almost all commercially available VFD's are designed for 3-phase motors.

    Very small 1-phase motors ( ceilling fans and the like) can be somewhat controlled by varying the voltage level applied to them.

    For small projects use a DC motor fed from a rectifier circuit. Once you get to 1/2 HP or so, move to a 3-phase motor. Note that low horsepower VFDs can be fed by a 1-phase AC source.

    · Also note, your table saw probably has traditional Ac motor but the router has a brushed, "universal" ·motor which actually can run quite nicely on DC.

    Cheers,

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Tom Sisk

    http://www.siskconsult.com
    ·
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