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do speed controllers damage routers?

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  • do speed controllers damage routers?

    I have a Porter Cable 690LR single speed router that I would like to use a speed controller on. It seems like some people say it will harm the router and others say it is fine. Porter Cable said not to and a guy at a local tool shop also said it would burn out the router. Everything I have read online seems to say it is okay. So what is the real story/ Do add on speed controllers burn out single speed routers? If they do, why do they even make them?

  • #2
    Re: do speed controllers damage routers?

    Do add on speed controllers burn out single speed routers?

    If they do, why do they even make them?
    These are both good questions and I am curious about the first one too.

    On the second Q I have a couple related questions of my own:

    Do you know of any speed controller that is manufactured or marketed by a company that also manufacturers routers?

    I can't think of one. I wonder why that is? Maybe because they know they will damage the router.

    Or maybe its because they want you to buy a variable speed router, the latter being more profitable for them.
    "When we build let us think we build forever. Let it not be for present delight nor for present use alone. Let it be such work that our descendants will thank us for, and let us think, as we lay stone upon stone, that a time is to come when these stones will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, "See! This our fathers did for us."
    John Ruskin (1819 - 1900)


    • #3
      Re: do speed controllers damage routers?

      With a router you would like to have constant speed but to have it user settable. This requires some manor of speed measurement. A simple method would be to use a small coil of wire and a small permanent magnet. Then using IC chips and more on a circuit board a frequency measuring circuit could be had that would very Voltage across the main motor windings. Try to think of a feedback circuit if you can. The problem would be trying to do this with an already made single speed motor.

      You can use a variable autoformer type transformer like a PowerStat or Variac but the speed will drop as you apply a load to the motor. You need one rated a minimum of 15 Amps continuous duty as well and they make the cost of a new deluxe router seem pretty nice.

      Please don't use a little light duty SCR type speed control. You'll just blow it up.

      For what it's worth look at the differences in a Milwaukee 1660 (single speed) and 1663 (variable and regulated speed) heavy duty 1/2" spade handle drill. Please look at the differences in motor parts.

      1660 Parts List -$file/54-10-0127.pdf
      1660 Wiring Diagram -$file/0539.pdf

      1663 Parts List -$file/54-10-0225.pdf
      1663 Wiring Diagram -$file/0675.pdf
      Last edited by Woussko; 01-24-2009, 11:48 AM.


      • #4
        Re: do speed controllers damage routers?

        Originally posted by Woussko View Post
        Please don't use a little light duty SCR type speed control. You'll just blow it up.
        Actually 2 SCRs in parallel (one in reverse) will do a better job than a triac.


        • #5
          Re: do speed controllers damage routers?

          A triac is two SCRs back to back with a common gate. The benefit to using a triac over two SCRs is that the triac has everything on the same substrate. To a reasonable tolerance, both sides of the triac conduct identically. Two seperate SCRs with their gates tied can have slightly different turn on/turn off characteristics.

          What is more important for a motor speed control is to have protection for the big-ole' (technical term) inductive kick that happens when the triac (SCR) is turned on. Instead of ramping up nice and slow, you get a sudden increate in voltage (high dV/dt) and the coil in the motor does its job as an inductor and creates a correspondingly high current.

          The snubber circuit in a cheapo light dimmer can't deal with this and will be blown away. A better and still inexpensive solution is to use a "thyristor" insted of a triac or two SCRs and still add an RC snubber. The time constant of the snubber should ideally be matched to the intended load but that isn't likely in a comercial speed controller. And even better method uses a device called an IGFET which doesn't rely on the voltage dropping to zero to quench like SCR-ish devices do. Using an IGFET you can actually shape the waveform and keep nice clean low slew rate zero crossings.

          All that aside, you are still running in an open loop configuration and the reduced RMS voltage and higher frequency content will in time take their toll on the motor. But in my opinion (and opinions are like...) the difference would be 1,000 hours without the speed controller and 995 with the controller. If the router doesn't already have a speed controller or other sort of speed feedback system, the simple router speed controllers are fine.


          • #6
            Re: do speed controllers damage routers?

            I suggested two SCRs because they will use each side of the sine wave thus fully turning off and cope better with inductive load.

            PS: can you help me figure out what resistors controls the charging current in a dewalt charger, I got the schematic and want to modify a charger from 2.8 A to 500 mA to charge AA batteries.