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DIY Variable Speed Controller for otherwise single speed hand tools?

Discussion in 'General Electronics' started by Steve Thomas, Jul 9, 2004.

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  1. Steve Thomas

    Steve Thomas Guest


    I have a little Black & Decker Sander that is just the right size for
    detail work, but sometimes on finer pieces of wood, it's too
    aggressive (13,000 orbits per minute).

    I was wondering if I built a device from a standard 110V Lamp Dimmer
    Switch (basically a short extension cord with a single gang work box
    inline to vary the power to the device) if this would accomplish my

    Could this cause damage to the motor itself?

    I know that Dremel makes a foot-pedal switch that can be used to
    control their tools in a similar fashion, but I am concerned that a) a
    larger motor might not work with it and b) I want to be able to set
    the speed and then forget about it, not keep my foot on a pedal.

    Thanks in advance for your help.

  2. Nirodac

    Nirodac Guest

    I wouldn't use a light dimmer. But, most hardware tool stores sell variable
    speed controls that you can plug your sander into, then plug the other end
    in to the wall outlet. They have a rotary dial to set the speed. They are
    intended for routers, but would work just as well on a sander. They are
    built for inductive type loads (like motors) and not resistive type loads,
    like light dimmers.
    Here's one example;
  3. Guest

    In most cases, these speed controls are nothing more than a light
    dimmer. Perhaps with a bigger triac to handle the startup surge
    better, but a dremel is a pretty light load anyway.

  4. Suraj

    Suraj Guest

    Ya,I agree that 13000 rpm is too much for fine woodwork.But it depends
    on the kind of abrasive you use.Your solution of making use of a
    dimmer switch will work perfectly.But make sure that the load of the
    motor matches the current rating of the switch.Again if you use a
    fixed step switch,then you have a lesser number of speed selections.So
    try to use a dimmer which has a rotary knob (a preset which is
    adjusted to change the firing angle of some kind of thyristor inside
    it).That should take upto 200W easily.
    I dont see any reason for this process to damage the motor.But it may
    damage the switch if you dont comply with the ratings:)
    Now,if you want to go for a serious and permanent solution,you will
    have to use control circuits based on microcontrollers,tachometers and
    thyristor based power electronics stuff.

  5. I have a queastion, Doesn't light dimmer work by delay gating of
    the ac cycle? which means the output is no longer a true sine wave.

    I dont think this suitable for induction motors, But since high torque
    power tools are not induction motors.

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