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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.

  1. Steve Thomas

    Steve Thomas Guest

    Greetings:

    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
    task.

    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.

    Steve
     
  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;
    http://order.harborfreight.com/EasyAsk/harborfreight/results.jsp
     
  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.

    -Chris
     
  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.

    regards
    Suraj
     
  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.

    ,Fernan
     
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