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  • celing fan motors

    Can someone point me to source of solid information on the kind of motors used in those fans and the technology used to vary the speed??? I know they Aren't the usual sort of motors we find in tools etc.
    The occasion is the one in my daughters TV room has some unusual ailments. and I've looked into the electronics (I've done that all my working life as an engineer) and the two relays and 3 5 mic caps are somehow what is used to vary the speed. So What is the motor type and its operation etc???
    Thanks for any sources to educate me.
    ...lew...

  • #2
    I do not have a source for you. And several technologies are, or have been, used in ceiling fans, so there may not be just one choice here.

    BUT

    From what you say, it sounds like your motor is a variety of "PSC" motor, one that uses one capacitor as both the start and run capacitor. That makes it an induction motor, which probably has 3 speeds, since most do.

    The speeds are set by changing the number of poles.

    Say, there are 24 poles, with the polarity such that every other pole is reversed. That can be done by using one winding for poles 1, 3, 5, and so forth, and another for poles 2, 4, 6, etc. By connecting them correctly, the odd number poles can be made opposite to the even number poles. The number of poles sets the speed. A 4 pole motor, 2 N (north) and 2 S (south) poles, runs close to 1800 rpm. So a 24 pole motor, with 12N and 12 S poles, would run at 1/3 that speed, or close to 600 rpm.

    By reversing one of the windings, then there are 24 poles in phase, with "imaginary" or "consequent" poles between them. Bottom line is that the motor acts as if it has 48 poles, and goes at half the speed, or 300 rpm.

    To get the third speed, there is probably a third winding, wound to form more poles than the other winding set, and that may use a second capacitor. The slowest speed can also be set up with another capacitor so that it relies on "slip" to add the last speed. The slowest speed also takes the least power, so relying on slip is potentially possible

    There are many possible combinations now that did not exist 20 years ago.

    Newer fans may have a different type of motor, and may even have a small VFD. "Permanent Magnet AC" motors, often used in small fans, can have variable speed without a VFD, and that is another way to get several speeds without the cost of a small VFD.
    1601

    Keep eye on ball.
    Hashim Khan

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    • #3
      Hi Lew
      I recently had to replace the pull chain switch that controls the speed in one of those fans. For low speed it connected a capacitor to a winding. For
      medium speed, it connected a second cap in parallel with the first cap. For high speed, it bypassed the caps entirely.

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      • #4
        Originally posted by RichR View Post
        Hi Lew
        I recently had to replace the pull chain switch that controls the speed in one of those fans. For low speed it connected a capacitor to a winding. For
        medium speed, it connected a second cap in parallel with the first cap. For high speed, it bypassed the caps entirely.
        That is a "slip" type control, most likely..... changing the series impedance, using the capacitor to drop voltage because that does not waste power or get hot.
        1601

        Keep eye on ball.
        Hashim Khan

        Comment


        • #5
          Yea it can't be changing the number of poles as there is only one lead from the "controller" to the fan motor. It has to do with the 3 caps of 5 mic (Sure wish the Mu was easier to access, course some folks wouldn't have the fonts to accept it) In any event I am curious about the theory and WHAT exactly the changing capacitor value does to vary the speed. If it's only a lossless dropping voltage or some phase changing function etc. So the motor can't wound like the common induction ones or I don't see how it would start.
          Thanks everyone. (Still scratching my head) :-)
          ...lew...

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          • #6
            Standard induction motors do not change speed well by voltage changes. They can, and that has been used for speed control, but it is tricky. It works better with PSC type and shaded pole type induction motors, and they start up and run without start switches. It only works well with a load that changes significantly with speed, like a fan. If there is no load, then they all tend to run at near-synchronous speed like any induction motor.

            But with a fan load, for instance, the speed depends on the amount of power put into the motor. At lower voltage, the speed drops until the motor torque is balanced by the reduced load.

            If there is an electronics package along with the motor, then it may be another type.
            Last edited by J Tiers; 06-28-2019, 08:24 AM.
            1601

            Keep eye on ball.
            Hashim Khan

            Comment


            • #7
              Fan motors usually vary the speed by changing the voltage. This is a reliable way to do it because of the load caused by the fan itself. They can be rewound on purpose with extra winding, which in theory would keep the same speed if you would increase the voltage. For instance, for 230v 50Hz, they wind the motor for 230, 280 and 300v. Since the supply is always 230v, the motor connected for 300v will struggle to reach full speed due to the lack of power and stay at a lower speed without damage. If you remove the fan, then there is a no load situation and the shaft will speed up. When you connect it to the 230v winding, it will then speed up to the maximum speed.

              The same will happen to a single voltage motor if you reduce the voltage. This can be done with a step down transformer with a few taps, a series resistor (this will waste the power dissipated in the resistor) or the equivalent, like mentioned before, series capacitor to lower the voltage with minimal loss.

              Naturally, the motor must be designed to withstand this and the efficiency of these motors is very low.
              Helder Ferreira
              SetŮ’bal, Portugal

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              • #8
                https://en.wikipedia.org/wiki/Ceiling_fan A very comprehensive article on the evolution of ceiling fan motors from the 1880's until today.

                RWO

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