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  • Help with DC motor speed control?

    I happened across a small, used treadmill the other day, and hauled it home for the cost of tossing it in the truck.

    It turns on, but I can't get the motor going. There's a spot that looks like some magic smoke escaped from the heart-rate/speed-readout board, but that appears- key word- to be seperate from the actual motor speed controller.

    Anyway, just from a casual glance at the speed controller, it looks like it might be as simple as stabbing in a pot in place of the heart-rate board. Lower left corner:



    If that's the case, it looks like it might almost be easy to use this thing. Yank the motor, controller and transformer, plug in a pot and away we go. Maybe?

    Here's the PN of the speed controller:



    Another board that I'm not entirely sure what it does, but it's 'between' the heart-rate board and speed controller:



    And for good measure, one of the motor data:



    I haven't unplugged or unwired anything, other than pulling the plug off the heart-rate board so I could dismantle part of the stand. If it's as simple as connecting a pot to those two terminals, what value and capacity pot do I need?

    And is this thing really a 1HP? The motor is only a bit bigger than a can of Fosters' beer- I have a hard time believing it's three times the power of the four-times-larger 1/3rd HP 110vac motors on either of my lathes...

    And last- any guesses on the max RPM? Doesn't seem to say anywhere.

    Doc.


    Doc's Machine. (Probably not what you expect.)

  • #2
    Doc,
    the three legs labled speed pot, should do the trick for a pot. I will look for you when i get to work in the am for a pot rating from a similar machine. I sell and service this stuff for a living. For what it is worth about the motor, they usually put out rated horsepower untill just after they are unboxed . the manufactured for weslo is our industries version of the harbor freight crap. Not bad if you are not going to use it much.

    Comment


    • #3
      The typical pot value for one of these controllers is 5K.
      Pretty much any power rating will work.
      Just as easy to use as you surmise.

      Alex
      Alex

      Comment


      • #4
        I got a few treadmill motors laying around,most I have are accurate hp wise,but the rpm is in the 4500-6000 range which expains the size.
        I just need one more tool,just one!

        Comment


        • #5
          That appears to be a reasonable controller, it has all the right adjustments, min& max speed, IR compensation, and current limit.

          I notice that apparently they made some changes to the wire colors to obey US standards... no green power wire!

          The power is indeed developed at high speed, whch is the major drawback of the motors. Slowing them more than a little will lose power, since they have little torque, and not much overload torque, especially with the current limit set right.

          Probably 3:1 or 4:1 speed range in general, more if you do not need low speed torque. You will need some back-gear type arrangement of pulleys to get the 4000+ rpm down to the usual 1750 or 1150 rpm motor speed. Then you can talk about slowing from that point.

          The "extra" board is to power the heart rate board and display etc, as well as possibly part of the controller "brains", looks like it may have a voltage regulator, as well as a relay that may start the motor.

          A pot might well fix it. Be aware that the pot and wires are likely at line voltage unless there is an optocoupler on that control board.

          [This message has been edited by J Tiers (edited 02-22-2006).]
          1601

          Keep eye on ball.
          Hashim Khan

          Comment


          • #6
            there's an optocoupler.

            U1 looks like.

            What is the part # on U3?

            5K is about right too for the pot.

            still treat it like line voltage.

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            • #7
              I've got one of those driving an 8" 4-jaw chuck in a vertical setup. Granted it doesn't have much punch on the low end but it sure spins that chunk of semi-steel just fine. I'd have to measure the pulleys but I set it up with about a 3:1 reduction.

              Your PWM board looks more advanced than mine. I don't have all the fine adjustments. I used the original slide pot that was mounted in the console. The distance, calorie and heart rate monitor console was standalone.

              Comment


              • #8
                Ah-yes, I finally found U1.

                Only opto-couplers are typically available in white packages.

                Toshiba makes a series of opto gate drivers, I want to say they are TLP-26 or a similar number....memory escapes me.

                Good to 25kHz switching frequency for PWM. NOT good for 250 kHz, as a competitor of ours seems to have found out.........

                That may well be one if the controller is a PWM type. Otherwise they have some that would be good for SCR or triac drives also.

                [This message has been edited by J Tiers (edited 02-23-2006).]
                1601

                Keep eye on ball.
                Hashim Khan

                Comment


                • #9
                  Quite likely that you have to turn the pot to minimum speed before the thing will start the motor. I got tricked by this until I did that. I guess I was expecting the motor to start right up at the speed that was set, but no.
                  My pot was also 5k.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                  Comment


                  • #10
                    The opto on there is white. However all the ones I have in my stock are black. The controller I have is low volts DC to the pot, 10-12vdc I believe.
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      Okay, I'm keeping up with about half of what you've said so far...

                      A little more info, if it helps: The heart-rate board is programmable. It has (had?) selections for multiple users, and several LED bar-graph elements so you could program a "cycle". IE, light workout for a few minutes, then faster, then slower, etc.

                      I'm assuming that board fed a signal through the "unknown" board to the speed control, which did the actual voltage regulation.

                      There's also a speed readout, an LCD display that shows time, speed in MPH and a couple other things. It's actually a self-contained module, "snapped" into the heartrate board. Not designed to be removable, but it was obviously a seperate module they already produced, and made a place to snap it into this larger board. It has it's own case, connectors and mounts- I'm assuming it was a smaller speed/timer readout for cheaper versions of the treadmill.

                      In the picture of the unknown board (tread3.jpg) the small connector with the back wires, in between the wide white connector and the black relay-looking thing, leads to an inductive pickup on the motor flywheel, which reads a magnet embedded therein. That cable/plug pops out and plugs right into the back of that MPH box, into a socket labelled "speed".

                      Also on tread3.jpg, the two-wire white connector on the right edge leads directly to the two connectors on the speed controller board marked "speedpot".

                      Would a rough wiring diagram help?

                      Doc.
                      Doc's Machine. (Probably not what you expect.)

                      Comment


                      • #12
                        The motor controller is fed a varying voltage from the console board. The controller requires a voltage that varies from zero to +10 or so for the complete range of speeds. This only takes two wires, one for ground and one for the voltage input to the motor control speed input.

                        If you use a pot the motor controller has a 10-12vdc reference output that the pot is connected to. One side of the pot goes there, the other side goes to the ground terminal and the center tap of the pot goes to the variable voltage speed input. 5k to 10k should work just fine. Use a linear taper pot for best results.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Doc, the standard is black (L), white (W) and red (H) from the circuit board, you can see those labeled on the controller heat sink.
                          Hook the wiper (center terminal) of your 5K pot, to white (W), then the two remaining connectors to either of the outer terminals on your pot.

                          Alex
                          Alex

                          Comment


                          • #14
                            That seems easy enough. I'll try digging up a potentiometer tomorrow and see what I can find out.

                            Power comes in through a big transformer screwed to the frame, as well as that smaller transformer and the black relay looking thing. Hopefully that too can be reduced somewhat...

                            Doc.
                            Doc's Machine. (Probably not what you expect.)

                            Comment


                            • #15
                              The two wire xformer screwed to the frame is a choke, you'll want that in what ever application you find for your motor and controller.
                              as for the other board, that is not a part of the motor controller.

                              All you need is 120 AC fed to the controller (with the hot line through the choke and switch/fuse/breaker of your choice), two wires going from the controller to the motor, and three wires connecting the 5K pot to the appropiate lugs.

                              Alex
                              Alex

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