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  • dc motor control

    there have been several threads recently on this topic.

    i just received this and it seems to work well off a rectifier:

    http://www.ebay.ch/itm/270857708190?...84.m1439.l2649

    does anybody think there is anything wrong with it, as the devices recommended were much more complicated/expensive?
    Last edited by dian; 03-26-2012, 12:41 PM.

  • #2
    That is just a simple triac or bridge and SCR controller, there is no accel/decel, current limit or other features.
    A better solution would be one of the KB or Baldor SCR or PWM drives off ebay.
    They can be had for as low as $20-$30.
    They will control DC as well as Universal motors.
    If that unit is just a triac, it would be limited to Universal motors.
    Max.

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    • #3
      Dele
      Wrong info
      Last edited by MaxHeadRoom; 03-26-2012, 01:52 PM.

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      • #4
        well, it runs a 600w dc motor very well. my understanding of electronics is very basic and there is no specification on the the three-pin-device that is cooled, so i really wonder what it really does.

        Comment


        • #5
          "3-pin device"

          Originally posted by dian
          well, it runs a 600w dc motor very well. my understanding of electronics is very basic and there is no specification on the the three-pin-device that is cooled, so i really wonder what it really does.
          The 3-pin device contains the Magic Smoke, under considerable pressure. Be very careful not to vent it!

          -bill

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          • #6
            Originally posted by gearedloco
            The 3-pin device contains the Magic Smoke, under considerable pressure. Be very careful not to vent it!

            -bill
            I am not sure that circuit board would sustain a 3.8Kw load either
            Max.

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            • #7
              duplicate post
              Last edited by MaxHeadRoom; 03-26-2012, 04:57 PM.

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              • #8
                Originally posted by MaxHeadRoom
                I am not sure that circuit board would sustain a 3.8Kw load either
                Max.
                Remember that Watts is EI. Volts times Amps across the item consuming the power. The SCR/Triac is going to have extremely low voltage across it, as its resistance is very close to zero when conductiong. Its restance when not conducting is essentially infinite, so no current is flowing.

                So, 3800 Watts at 220 volts would be 17.27 amps. The voltage drop across the SCR/Triac would be in the range of a millivolt (or less,) resulting in 0.01727 Watts across the SCR/Triac.

                The device and circuit board should be able to withstand that.

                Pops

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                • #9
                  Originally posted by armedandsafe
                  The device and circuit board should be able to withstand that.

                  Pops
                  My experience with power supplies, that foil is going to act as a fuse!
                  Max.

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                  • #10
                    Like other have said it is basically a lamp dimmer. I would not use it. They have awful speed regulation at lower speeds. With no load it is not noticeable but when you start to put a load on it it will be apparent.

                    Get one of the KBIC controls. They are what you want.

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                    • #11
                      Originally posted by macona
                      Get one of the KBIC controls. They are what you want.
                      Shhhh! It's hard enough already to find 'em dirt cheap.
                      Milton

                      "Accuracy is the sum total of your compensating mistakes."

                      "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

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                      • #12
                        Macona, how do you reverse the motor using a KBIC board?

                        Patrick

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                        • #13
                          The 2 quadrant type require the DC output to the motor be reversed by relay or switch, but you have to also make sure to close the I1 & I2 terminals so the motor goes through the accel mode otherwise you could go to reverse in full voltage.
                          If you want to reverse without relay, the 4 quadrant versions will do it and also allow ±10vdc control instead of 0 to +10.
                          These also have dynamic braking as a feature of the 4 quadrant control.
                          Max.

                          Comment


                          • #14
                            Originally posted by armedandsafe
                            Remember that Watts is EI. Volts times Amps across the item consuming the power. The SCR/Triac is going to have extremely low voltage across it, as its resistance is very close to zero when conductiong. Its restance when not conducting is essentially infinite, so no current is flowing.

                            So, 3800 Watts at 220 volts would be 17.27 amps. The voltage drop across the SCR/Triac would be in the range of a millivolt (or less,) resulting in 0.01727 Watts across the SCR/Triac.

                            The device and circuit board should be able to withstand that.

                            Pops
                            Well, the millivolt idea is not correct at all.....

                            The true voltage in the "on" state is often more like 1.5 to 2 volts, or around 2 watts per amp. That is why the heatsink is used.

                            yes, it is a light dimmer circuit, basically. Used with a motor, it may or may not (usually not) produce a stable speed of the motor. In some cases, it may actually have an unstable mode where it will not correctly control speed, often at slower speeds.

                            The "KB" type controllers are made to do a very good job, and they do.
                            1601

                            Keep eye on ball.
                            Hashim Khan

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                            • #15
                              Originally posted by J Tiers
                              Well, the millivolt idea is not correct at all.....

                              The true voltage in the "on" state is often more like 1.5 to 2 volts, or around 2 watts per amp. That is why the heatsink is used.

                              yes, it is a light dimmer circuit, basically. Used with a motor, it may or may not (usually not) produce a stable speed of the motor. In some cases, it may actually have an unstable mode where it will not correctly control speed, often at slower speeds.

                              The "KB" type controllers are made to do a very good job, and they do.
                              I hereby stand corrected. I was going on memory from when I was using them in the early 60s, just after they were introduced. I was using them with much higher voltages and frequencies.

                              Pops

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