B50K Potentiometer Controlling 1300W 220-240V-50Hz Motor - Need More Control

Discussion in 'General Electronics Chat' started by Unicorn0578, Apr 6, 2018.

  1. Unicorn0578

    Thread Starter New Member

    Apr 6, 2018
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    Hello,
    I wonder if you could give me some advice on a project I am working on. I am building a homemade pottery wheel from a paddle mixer.
    Everything is going very well and I have managed to expose the B50K Potentiometer which I will adapt into a foot speed control.
    Part of my query is the Pot low end does not stop the motor and the slow speed is not slow enough.
    The other problem is the fast speed is too fast.
    I wondered if I could wire in an additional Pot to set the Maximum speed at the mid point and then another Pot to control the speed from 0 to the mid point.
    I purchased another B50K Pot which works the same as the original. I thought perhaps a new model may increase the sensitivity.
    I also purchased a 10 turn 10K Pot which does not vary the speed in any way.
    Any advice would be much appreciated
    Picture below to help understanding. Can provide more info or Pics if needed.
    Thanks in advance
    Colin

    [​IMG]
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    There is more to the speed control than just that pot. We would need to see a schematic of the circuit it is part of to see how best to adapt it.
    Does rotating that knob clockwise increase or decrease the speed?
    Depending on the motor type it may not like running more slowly, or have much torque at a lower speed.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Is it possible you are using the wrong kind of motor for this application?
    I would guess the paddle mixer is a Universal motor with a triac controller, the problem is that this type of motor operates in a run-away condition and rpm is limited mainly by the applied load.
    It is not a suitable motor for a pottery wheel.
    I would have suggested a ex DC Treadmill motor for a better soulution, in conjunction with say an original controll such as the simple MC-60.
    Max.
     
  4. MisterBill2

    Well-Known Member

    Jan 23, 2018
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    One detail is certain, which is that the small 50K pot is not in series with the motor, but rather controlling some speed control device, either a triac or an SCR. In order to avoid a whole lot of problems from getting into circuitry that you don't understand, I suggest leaving well enough alone with the motor speed control and instead using a belt type speed reduction arrangement. Not only will it provide the speed that you seek, it will also multiply the torque,which more torque will be handy for a potter's wheel. Then you can also add a means to loosen the belt to stop the turntable. Somebody with a lot better technical background may be able to modify the control circuit, but still, stopping would be an issue, and low torque could be a serious problem.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would think with a potters wheel you need fairly constant RPM and you won't get that with a Universal motor unless feedback is applied.
    One asset, series motors are high torque motors, This is the reason they are used as automotive starters, but need a load to control keep the RPM reasonable.
    You MAY get acceptable results with high reduction, you don't need high rpm for a Potters Wheel.
    Possible scenario, say you are using the wheel and apply a certain load, as soon as the load is removed the rpm goes up with undesirable result.
    Max.
    .
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Looks like its an ordinary dimmer/speed controlled motor, if 50K isn't slow enough try 100K, the problem will be that the motor is a Universal type, which the speed tends to increase without a load.


    motor-speed-regulator-schematic.gif
     
  7. dendad

    Well-Known Member

    Feb 20, 2016
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    Be VERY careful as the pot connections are not isolated from the mains so are potentially lethal to touch!
     
  8. MisterBill2

    Well-Known Member

    Jan 23, 2018
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    Since the device was intended to be used as a paddle mixer it seems reasonable that it would include a speed controller with some built in feedback to tend to hold the speed fairly constant. I have seen the speed controller circuits that do that and it is usually just a few extra parts. Of course the very best choice would be to control the speed with a foot pedal. Then the user would just release the pedal to slow the rotation. And with a stop-start button next to the pedal complete control would be simple. A fairly high speed reduction ratio should be possible in one stage, given the typical potter's wheel setup.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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  10. ian field

    AAC Fanatic!

    Oct 27, 2012
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    The bottom of the range is probably limited to make it difficult to stall.
     
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