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  • DC treadmill motor question about power supply

    I took apart a treadmill and got a nice DC motor, and it's power supply. Then while fiddling around with it I dropped the power supply board on a conductive surface and the magic smoke came out.

    I have seen references to using a simple switching PS like this https://www.ebay.com/itm/AC110V-220V...4AAOSw3F5dqCWM and running the ouput through a bridge rectifier and then to the DC motor.

    Question 1) Is this a bad idea for some reason?
    Question 2) My DC treadmill motor has 4 wires, +, -, and CBA1 CBA2 ... I would assume + and - are the right ones?
    Question 3) What will this lose compared to using an original treadmill PS from a diffferent treadmill?

    Thanks
    Dan the Chemist

  • #2
    Hey Dan.

    Pretty sure that item you reference puts out AC. You need DC.

    The thing you are calling a PS, is better called a motor control board. Click here to see some on Ebay.

    Take note that some of those take a DC input and produce a varied DC output. What you want is one that
    takes an AC input and gives you varied DC output.

    The black and red are the motor power leads. The other two are probably to a thermistor. (I usually pull those off)
    John Titor, when are you.

    Comment


    • #3
      Dan. I just did the exact same thing and it worked fine for me. I used the same controller and a bridge rectifier with a 90v dc motor. The pot that comes with the controller doesn't allow much speed control. Not a problem for my application as I only needed top speed. Check out this vid for a better explanation.

      https://www.youtube.com/watch?v=_NmAFZMAfH8

      Comment


      • #4
        I'll take a guess here and suggest that CB means circuit breaker- if those two wires are a circuit breaker you would wire one of them to a motor wire (one of the other two), then feed voltage to the remaining wires. Reversing the voltage should reverse the motor.

        This does make the assumption that it's a permanent magnet DC motor. It should be easy enough to tell- a PM DC motor doesn't have field windings. Most of the time a dc motor will exhibit some 'cogging' as you turn the shaft by hand- if you get that it's a PM motor. An easy test is then to apply some voltage to what should be the motor wires. 12 volts is enough to make it run, though it will be slow.

        In my case, the motor I used on my lathe is a treadmill motor, PM and DC. I run it using a transformer with multiple tapped windings and a simple bridge rectifier and capacitor. This doesn't give speed regulation, but it does give the ability to give various speeds at no load. Loading it down, as during a cut, will reduce the speed, but in my case I use that as an indicator of how much I'm loading it down. An exact and non-varying speed isn't critical to me, so it's a done deal, no electronics required.

        There are speed control made to run these motors, and they will likely have some form of regulation built in. These can be very simple circuits, probably needing only the ac input voltage and a 5k pot for speed control. It doesn't have to get all fancy with features, led readouts, etc. I've never used an off the shelf one, but doesn't KB make these?
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

        Comment


        • #5
          This will be the motor for my magnetic drill project. I want to use it for both drilling the holes and then machine tapping, so I need to have high and low speeds. The high speeds would range over those speeds appropriate for the tap drills for 10-32 to 1/2-13, although I will be using mostly 1/4, 5/16 and 3/8. The low speed just should be low enough for machine tapping. I figure I will use a DPDT switch to reverse the drill to remove the tap.

          So I don't think the RPM has to be very accurate - just somewhat in the right ball park for the large and small drill sizes, and much slower for tapping.

          Comment


          • #6
            Those are generally high rpm, you will need a belt reduction. I'd do as much belt reduction as possible, because torque and power suffer as you reduce motor rpm. You want to keep the motor at as high a speed as possible, and just have the spindle slow.

            1601 2137 5683 1002 1437

            Keep eye on ball.
            Hashim Khan

            If you look closely at a digital signal, you find out it is really analog......

            Comment


            • #7
              yeah, you'll need a crazy azz amount of belt reduction to get down to tapping speeds. I tap on my drill press alot and have (I think) an 8:1 reduction via a countershaft with the speed dialed down to just above stalling. That's mostly for small stuff 1/4-20 and below, as I don't have a dedicated tap holder and the taps will spin in the chuck (I know, I know) for bigger stuff.

              Comment


              • #8
                An SCR/TRIAC controller with a full wave bridge rectifier may work to some extent, but it will tend to run the motor at a speed determined by the phase angle, especially under light load. It will work better when under a constant load. Another way to get better control would be by adding an inductor in series with the motor, but then you may have problems with inductive transients. Best way is true PWM, like this:

                https://www.ebay.com/itm/6V-90V-15A-...P/282704941288

                Click image for larger version

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                http://pauleschoen.com/pix/PM08_P76_P54.png
                Paul , P S Technology, Inc. and MrTibbs
                USA Maryland 21030

                Comment


                • #9
                  Heh.... That ad has USA all over it, but the price says CHINA in big letters...... Might not be getting any for a while either, "china" is pretty well shut down due to the virus, so say folks who are there now.
                  1601 2137 5683 1002 1437

                  Keep eye on ball.
                  Hashim Khan

                  If you look closely at a digital signal, you find out it is really analog......

                  Comment


                  • #10
                    I bought one of those Black Box Motor Controller,had no luck with it giving strong or smooth power.

                    Comment


                    • #11
                      The thing about the treadmill controller that I frazzled is that it provided good power at all speeds, and many of them were pretty darn slow. Treadmills can go just a fraction of an mph, but it still has enough umph to move a 250 pound buffalo standing on the tread. It does have a roughly 3:1 belt ratio in it's favor, but that's all it has. That is what made me favor the idea of using a treadmill motor for low speed applications. If I can't get the low speed for power tapping then the real advantage of this project is gone along with the magic blue smoke....


                      Comment


                      • #12
                        If you use a PWM controller such as one of the T.M. MC2100 versions, they will control down to zero rpm, they normally have to control a varying load such as low belt speed and heavy user.
                        A DC motor typically has maximum torque at zero RPM.
                        Often the simple Triac with bridge versions as shown in the video have very little built in features.
                        Max.

                        Comment


                        • #13
                          Originally posted by MaxHeadRoom View Post
                          If you use a PWM controller such as one of the T.M. MC2100 versions, they will control down to zero rpm, they normally have to control a varying load such as low belt speed and heavy user.
                          A DC motor typically has maximum torque at zero RPM.
                          Often the simple Triac with bridge versions as shown in the video have very little built in features.
                          Max.

                          The statement that "maximum torque is at zero RPM" is kinda true, but maybe not. It depends whether you are talking about the maximum it can ever produce, or the maximum it can produce steady-state, etc. And it depends on the type of motor.

                          There is torque and there is power and there is rpm. Motor designs vary, and treadmills vary. But there is one constant fact.... the motor will normally put out max power at the design "base speed", the speed it goes with the design load and full voltage applied.

                          A series motor does produce fantastic torque at low speed, and that is why those were always used as "traction motors". Treadmlls do not use them, typically, although some might.

                          Most of the treadmill motors are permanent magnet "shunt type" motors. Those have a base speed that is set by the design. That is where they produce the most power. Torque is generally constant at any speed, because the magnet is a constant field strength, and the coil wires can only take so much current before they overheat. (That gets much worse at low speeds.....)

                          Power is force x distance per unit time. So power is related to torque and rpm. If RPM is cut, so is power, unless torque can go up. There is a dramatic demo of this in the "This Old Tony" demo of the minilathe. That has all speed control via the electronics. At a low, but reasonably credible speed, he basically could not take a cut without stalling the lathe.

                          And, there is the problem.... If you cut RPM in half, power is cut in half too, because with a shunt motor, torque is pretty much proportional to current. Current COULD be held constant, BUT, typically the motor has a cooling fan, and it does not cool as well at half speed. So actually, the torque you can USE goes down, unless you put an external blower on it. At zero speed, you cannot run much continuous current or it will overheat, unless you have a blower on it.

                          Bottom line is that without a blower, you probably should not cut speed much below 1/3 of design base speed, if that much, if you expect to maintain torque. Yes, you can exceed that for short times, but you cannot be sure how short a time you have at any current.

                          To get the sort of torque needed for tapping with larger taps, you really need to run the motor as fast as possible and if you need a slow speed, use belt or gear speed reduction as your basic method to get there. Not only is that needed to make it work, but also, that will probably give you the best speed control.
                          1601 2137 5683 1002 1437

                          Keep eye on ball.
                          Hashim Khan

                          If you look closely at a digital signal, you find out it is really analog......

                          Comment


                          • #14
                            Just about all the reputable manufacturers of DC motors I have used, publish a spec sheet that shows the continuous torque curve and the momentary operating curve.
                            The continuous curve typically showing maximum at zero rpm.
                            This is necessary when the motor is typically operating in a servo application and requires a constant current at zero rpm to hold a position.
                            I did come across a T.M. that operated with a Universal motor and used the TDA1085 Motorola IC for control, originally intended for washing M/C motor controller, it had a 6 pulse/rev opto rev indicator back to the IC. in order to maintain the speed.
                            Typically T.M. controllers have a built in acel/decel rate and cannot be fed full voltage from zero.
                            Max.

                            Comment


                            • #15
                              The theoretical general curve is as you say. The background for it may be different. And that is not quite a "practical limit", but a "maximum capability". Somewhat like the specs on a vacuum cleaner, they are not ones you can actually use. How different they are depends on the motor design.

                              The torque is produced by the current through the windings. Provide that current, and the torque is there. it is the "providing the current" that changes.

                              At zero speed, ALL the supply voltage is available to produce current through the motor. There is NO guarantee from the theoretical curves, that the motor can stand that current for long without "letting out the smoke". The current required may be 2 or 3 times more than the rated current, giving 4x to 9x the normal heating effect, at the same time that the cooling capability is reduced due to speed reduction.

                              At maximum speed, the back EMF is high enough that only enough current can flow to supply the small torque needed to overcome friction and windage.

                              In between those, the torque is whatever the difference between the voltage and the back EMF can provide.

                              A KEY POINT THAT MUST BE REMEMBERED: The maximum torque curve is ONLY for the condition where the rated voltage is provided, and the motor is loaded down so heavily that it slows to the speed noted. THAT CURVE DOES NOT APPLY FOR THE CASE WHERE THE VOLTAGE IS REDUCED TO SLOW THE MOTOR DOWN TO THE SPEED YOU WANT.

                              The ACTUAL motor curve for continuous operation would be one where the torque increases as you move down from the maximum no-load speed, and then reaches a maximum around the rated power point. From there down to zero, the "PRACTICAL" torque is going to be limited by the capability of the motor to get rid of heat at each speed, and will probably decrease to a lower value at zero.

                              Servo motors are a special case. The heat lost is resistive heating, and a servo is often made with larger wire than necessary, so that the heat loss at any current is less than typical, and may have heatsink fins etc.. That allows a higher continuous current (and so higher torque) at zero speed than most motors could take.

                              Check this spec

                              https://www.hansen-motor.com/pdf.php...1inDCMotor.pdf

                              Notice that there is a "stall torque" and a "stall current", that are different from the specs under running conditions. If you do the "motor math" you will find out that the "stall current" is just the rated voltage / motor resistance. They do not claim that is a usable motor running condition, they just say that the motor can do that for some unspecified time as a maximum.
                              Last edited by J Tiers; 02-13-2020, 12:14 PM.
                              1601 2137 5683 1002 1437

                              Keep eye on ball.
                              Hashim Khan

                              If you look closely at a digital signal, you find out it is really analog......

                              Comment

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