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electric motor speed

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  • 08-07-2020 12:25pm
    #1
    tommyboy26
    Registered Users Posts: 2,117 ✭✭✭


    I am building a bench top belt sander. I have an electric motor that runs on AC power that i want to connect a on/off switch and a cheap way of controlling the motor speed.

    I have a little bit of electrical experience and was thinking if i added a potentiometer between the on/off switch and the motor to control the resistance to the motor, that this would control the speed of the motor.

    Am i right in thinking that will work or am i way off?


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    #2
    autumnalcore
    Registered Users Posts: 825 ✭✭✭autumnalcore


    tommyboy26 wrote: »
    I am building a bench top belt sander. I have an electric motor that runs on AC power that i want to connect a on/off switch and a cheap way of controlling the motor speed.

    I have a little bit of electrical experience and was thinking if i added a potentiometer between the on/off switch and the motor to control the resistance to the motor, that this would control the speed of the motor.

    Am i right in thinking that will work or am i way off?

    Way off, what kind of motor is it, how many watts, you would normally use an appropriate motor and pulleys to control the speed so that you don't lose torque, a belt sander that bogs down is heartbreaking.


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    #3
    tommyboy26
    Registered Users Posts: 2,117 ✭✭✭tommyboy26


    autumnalcore wrote: »
    Way off, what kind of motor is it, how many watts, you would normally use an appropriate motor and pulleys to control the speed so that you don't lose torque, a belt sander that bogs down is heartbreaking.

    motor is:
    200 watts
    180VDC
    1.5 A
    2100 rpm

    would i need a variable speed drive? I am trying to do it for as cheap as possible


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    #4
    Lenar3556
    Registered Users Posts: 1,350 ✭✭✭Lenar3556


    tommyboy26 wrote: »
    motor is:
    200 watts
    180VDC
    1.5 A
    2100 rpm

    would i need a variable speed drive? I am trying to do it for as cheap as possible

    A potentiometer will reduce the speed, but also the effective power at the same time, so not exactly what you want. The motor will be inclined to stall at lower speeds.

    A variable speed drive would be a much more effective way of controlling speed by adjusting frequency.

    Edit: I’ve just noticed it’s a 180V DC motor. Where did you get it and how do you plan to power it? In their interests of economy could you harvest speed control circuitry from a machine that it came out of?


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    #5
    Lenar3556
    Registered Users Posts: 1,350 ✭✭✭Lenar3556


    Tell me how wrote: »
    Your typical Potentiometer will heat up and disintegrate/explode at the power involved in even the smallest AC motor. That aside, speed control works by adjusting the frequency of the supply to the motor (nominal 50Hz from AC outlet)

    You can get Variable Speed Drives on Ebay for as little as €65.

    You could mount this in a box beneath the bench and connect your potentiometer close to the sander if you want to keep everything neat. In theory, with a VSD, you can increase the speed greater than the standard 50Hz but if you do so in this instance keep in mind that the bearings/belt were probably not designed for such speed.

    When you familiarise yourself with the VSD, you should be able to lock the max/min speeds to prevent someone else from running it in a way that was intended.

    But I notice he said the plate says 180VDC. Is he planning on running it on 230VAC I wonder, will it be suitable for this?


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    #6
    Tell me how
    Registered Users Posts: 21,517 ✭✭✭✭Tell me how


    Lenar3556 wrote: »
    But I notice he said the plate says 180VDC. Is he planning on running it on 230VAC I wonder, will it be suitable for this?

    I had missed that. I have deleted my post as it could be misleading.


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    #7
    autumnalcore
    Registered Users Posts: 825 ✭✭✭autumnalcore


    200w belt sander would hardly take the skin off a rice pudding. An angle grinder or drill body would be a better bet for driving it. If you only need a short belt you can get belt sander kits for grinders on ebay/aliexpress etc.. or you can pick up a combined bench grinder belt sander for well under €100


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