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  • Treadmill motor drill press problem

    Hi,

    So, I converted my drill press to use ye olde treadmill motor. It's not working like I hoped. No torque.

    I can grab the motor pulley (while wearing welding gloves) and stall it out immediately at any speed I'm willing to try. It just shudders, and I can easily hold it dead. Obviously, my new adjustable drill press doesn't work too well this way.

    The treadmill was old -- a 1991 vintage. I've checked the motor's brushes, which still have plenty of meat, and the comm looks healthy enough.

    The motor is a GE 5P80LY2A rated at 1.5 HP @ 120V DC. The controller is a GE 52A103470AAP1. Can't find much about either, probably due to the age.

    The controller is seeing 122 V AC. At minimum speed, the motor is only seeing 5.25 V DC and at max, about 40 V. There's a MAX SPEED pot on the controller board that doesn't appear to do much at low RPMs (predictably, I guess).

    I was a little surprised at the extremely low motor voltage, and perhaps it's not a huge shock that there's no torque down low. But, I can't even picture this thing running a treadmill effectively with the torque that it has. Both the controller and motor appear to work fine, though, which makes me think that something is wrong. Is the motor just old, demagnetized, and worn out?

    I have other treadmill motors, but they don't have the tach signal wires that this controller needs. When installed on the controller, they simply spin at top speed. I don't have another controller to test this motor.

    In summary -- proper speed, no torque. Why?

    Ideas? Thanks for any help.

    S
    Last edited by Stainless; 02-05-2013, 11:00 AM.

  • #2
    I don't claim to be an expert by any means, but I was wondering what RPM the motor in question is rated at for the HP claimed. If it is rated at high RPM (6000 or more) I would expect you need to use some form of gear reduction to get the torque required.
    Of course this may not be the problem at all and perhaps the permanent magnets have weakened with time and age or there may be a controller issue.
    MaxHeadRoom is probably one of the better resources here but others have a lot of good info as well.

    Comment


    • #3
      Originally posted by firbikrhd1 View Post
      If it is rated at high RPM (6000 or more) I would expect you need to use some form of gear reduction to get the torque required.
      Thanks for your response. There's no RPM range printed on the motor, but, with an approximate 3:1 belt reduction in the drill press, the chuck RPM range is between 160 and 1600 with this treadmill motor. So, I think I've got the reduction in the right range, but it's totally gutless even when I increase the chuck speed beyond 500 RPMs. The bit stalls in 1/8-inch bed frame metal.

      S

      Comment


      • #4
        [QUOTE=Stainless;828046]Hi,


        The motor is a GE 5P80LY2A rated at 1.5 HP @ 120V DC. .......
        The controller is seeing 122 V AC. At minimum speed, the motor is only seeing 5.25 V DC and at max, about 40 V. /QUOTE]

        If you are only putting 40 volts max on the motor, you are only getting about 1/9 the power it is rated at ( P=V**2/R). The problem could be that one of the SCRs is bad only allowing you to get half wave rectification, or the tach signal you are feeding the controller may be limiting you. You might try to reduce the tach feedback with a resistor network and see if it helps.
        To get work out of my treadmill motor, I have it geared down over 7:1.

        Comment


        • #5
          Not a definitive answer but --- I have set up about 10 different uses of a TM motor and find they can vary in performance pretty widely. I had a 2-3 do as you are experiencing, just would not perform (maybe thats why I ended up with them, original owner found the TM just wouldnt perform??) I usually have 2-3 control board around and have switched out with no change in performance. In fact, I seem to recall only 3-4 really meeting my expectations.
          If everything seems to be going well, you have obviously overlooked something........

          Comment


          • #6
            [QUOTE=Gary Paine;828059]
            Originally posted by Stainless View Post
            Hi,


            The motor is a GE 5P80LY2A rated at 1.5 HP @ 120V DC. .......
            The controller is seeing 122 V AC. At minimum speed, the motor is only seeing 5.25 V DC and at max, about 40 V. /QUOTE]

            If you are only putting 40 volts max on the motor, you are only getting about 1/9 the power it is rated at ( P=V**2/R). The problem could be that one of the SCRs is bad only allowing you to get half wave rectification, or the tach signal you are feeding the controller may be limiting you. You might try to reduce the tach feedback with a resistor network and see if it helps.
            To get work out of my treadmill motor, I have it geared down over 7:1.
            Hi Stainless
            Gary is most probably correct

            DC motors and controls can be a bit fiddly to set up. The controls that I am familiar with are Dart, KB Electronics, and Minarik.

            They require that the Torque and Speed be setup and matched to the motor.

            If the Torque setting and Intensity setting is too LOW then you have reduced power and speed

            BEWARE If you set them TOO HIGH The results can be VERY DANGEROUS Motor life can be shortened to to a few seconds.

            PLEASE be very careful with DC Current It can stop your heart in an instant.

            This Web Site will give you access to files on the set up of DC controls. Grab the PDF Manual that fit your motor output

            http://www.kbelectronics.com/Variabl...es_Chassis.htm

            Being a DC Motors nut case I have found this info invaluable.

            Eric

            Comment


            • #7
              Originally posted by Gary Paine View Post
              If you are only putting 40 volts max on the motor, you are only getting about 1/9 the power it is rated at ( P=V**2/R). The problem could be that one of the SCRs is bad only allowing you to get half wave rectification, or the tach signal you are feeding the controller may be limiting you. You might try to reduce the tach feedback with a resistor network and see if it helps.
              To get work out of my treadmill motor, I have it geared down over 7:1.
              Hi Gary. I thought that too, but the math doesn't seem to work. At 3:1, I'm seeing a maximum of 1600 RPMs at the chuck. So, about 4800 RPMs motor speed at 40 V. 80 V would produce an insane motor speed... closing in on 10k RPMs. Is that plausible? I'd need a spindle pulley the size of a toilet seat to get the thing spinning slow enough to use (or a jack shaft, I suppose). I don't see other treadmill conversions having to get that crazy.

              Am I way off in my thinking here?

              S

              Comment


              • #8
                There may be one issue if it is not the original motor?
                If the tach is not scaled properly you will not see max voltage out, although you should still have reasonable torque at low rpm.
                Try connecting a 100w lamp on the output in place of the motor, obviously it will go into maximum output (simulated runaway), but you can see at least if it is capable of high DC output.
                Test the motor on a automotive battery, this should supply appreciable torque at low rpm.
                Max.

                Comment


                • #9
                  Have you tried getting rid of the tach wires. I never use them. I haven't ran into a controller that demands
                  them.

                  Throw a volt meter on the output leads (without the motor) and play with the max rpm pot. If you don't see
                  a change .. your controller is bad order.

                  If you have a I.R. Comp pot .. that regulates speed under load.

                  If you can stop that motor with your hand ( which you should never be able to do ) .. it will never work
                  for your application.

                  My thoughts are .. Take that tach off.
                  John Titor, when are you.

                  Comment


                  • #10
                    Originally posted by mikeamick View Post
                    Have you tried getting rid of the tach wires. I never use them.
                    There are many of the older drives that cannot be configured without tach (velocity drives) and they error out or causes a runaway without it.
                    Modern closed loop drives have the option of velocity (feedback), open loop and/or torque mode, no F.B.
                    Also what can be done to try/test the other motors that do not have a tach is to rig up a small variable DC supply to simulate a tach, the polarity has to be the same as the motor, the rpm should track the simulated tach voltage.
                    Tach's generally range from 3.5v/1krpm to 25v/1krpm.
                    Max.

                    Comment


                    • #11
                      Bill Pace -- That's interesting. I haven't seen any treadmill motors fail in this way during my research, so I'm a little surprised to learn that it's not uncommon. I suppose there are good reasons why many of these things are rescued from the dump, perhaps in my case too.

                      velocette -- Thanks for the controller resource. I'm not totally sure if you were suggesting those for purchase, or to troubleshoot the one I have. The GE controller doesn't have any jumpers or adjustments, aside from the max speed pot that, as I mentioned, doesn't affect much in the RPM range that I'd use for metalworking. I don't think I'd buy a controller for this project rather than just hunting down another treadmill.

                      MaxHeadRoom -- Thanks for the tests, they're good ideas... I will try those things and see what happens.

                      mikeamick -- I haven't tried disconnecting the tach wires while using the GE motor, but I have tried other treadmill motors that do not have tach wires (more modern motors with the blue thermal switch wires). They ramp up to top speed immediately and do not respond to the speed control pot. In other words, it's all or nothing without a tach connection. So, this controller appears to need it. I will check the controller output voltage without the motor attached and see what's what.

                      Thanks for the responses, everyone. I am losing confidence in my hardware, but I'd be very happy to be proven wrong.

                      S
                      Last edited by Stainless; 02-05-2013, 03:09 PM.

                      Comment


                      • #12
                        Further to post #10.
                        The way a tach works is that the command and the tach are fed to a summing amplifier (Op-amp), as the motor accelerates and when the tach feedback reaches a value, dependent on the scaling adj. the tach voltage will cancel or offset the incoming dc command signal in the amp. and it will then hold the commanded rpm until the input command is changed, or something (load) tries to change the rpm.
                        If it does not see the tach signal to cancel it, the rpm will climb to maximum, i.e. the drive is expecting a tach voltage which never happens and the revs climb to maximum DC supply.
                        Max.

                        Comment


                        • #13
                          Originally posted by MaxHeadRoom View Post
                          Further to post #10.
                          The way a tach works is that the command and the tach are fed to a summing amplifier (Op-amp), as the motor accelerates and when the tach feedback reaches a value, dependent on the scaling adj. the tach voltage will cancel or offset the incoming dc command signal in the amp. and it will then hold the commanded rpm until the input command is changed, or something (load) tries to change the rpm.
                          If it does not see the tach signal to cancel it, the rpm will climb to maximum, i.e. the drive is expecting a tach voltage which never happens and the revs climb to maximum DC supply.
                          Max.
                          Although I've not had a motor with tach output to play with, that is what I expected. So, if really an op amp, the input impedance should be quite high to the tach leads. Then I would think one could hook a one leg of a potentiometer to the controller's positive dc output and the other leg to the negative dc output with the wiper connected to the circuit's tachometer input. Any pot value from 150k up to maybe a megohm should do it. The pot would provide a reference voltage from 0 to full (Presumably 100 volts?) If the speed setting were at maximum, this tach input would, I bet, provide speed adjustment, but wouldn't it be open loop? I'm thinking load/speed regulation would be poorer than with perhaps something like the KB controller. It should, though, provide the opportunity to see what kind of tach input voltage the board wants.
                          I am more and more thinking that if open loop voltage on those motors without tachs only hit 40 volts, we are looking at only a half wave output and that the high RPMs at 40 with essentially no load (3:1 pulley ratio to a quill) is because the peak voltage of the half wave were full voltage but the meter was averaging it out better than the motor. Heck, I've been really surprised to see my treadmill motor take off running on less than 5 volts, so spinning up no load to 100 volt spikes doesn't surprise me much.

                          Comment


                          • #14
                            This may not apply to yours, and apparently you cannot check.

                            BUT....

                            Most of the treadmill motors are rated at somewhere around 4000 rpm. Since torque is less as rpm goes up, that's a very suggestive point.

                            You state 1.5 HP. That should be almost 2 ft-lb torque at 4000 rpm, which I can see you stopping fairly easily by hand.

                            Slowed down to 120 rpm by electrical means, it represents nearly no power.......

                            So, your best bet is to at the very least increase your ratio, and give some more pulley steps. The torque you can get with a low ratio reduction is likely to be nearly nil.

                            You can check this. Get a rope, and weights (anything not very breakable that you know the weight of), and a pulley of known diameter. Change the weight until the motor can just lift it (you need a good hand on the switch, and a longer rope helps).

                            With the weight, and the known radius of the pulley, you will KNOW the torque, and can work the HP/torque/rpm formula backwards to arrive at a decent estimate of the rated RPM.

                            Since motors have back EMF, assume that the voltage at which your torque is produced is about 1/10 of rated..... usually the back EMF due to rotation is about 9/10 of the supplied voltage. Can be 95%.

                            If you know the rated current of the motor, check resistance and then use resistance x rated current to get the "driving" voltage , which is supply - back EMF.

                            DO NOT apply full voltage, that could be hazardous.....
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • #15
                              Just curious- is that a permanent magnet motor, or a wound field type? The PM type should be able to produce a fair amount of torque, which will remain fairly constant compared to the current draw. At very low voltages, the resistance of the motor will limit current, so you could have decreasing torque because of this. At higher voltages the current could easily rise to 10 amps or more, and the available torque would be higher. I'm not saying this is within the operating parameters for that particular motor, but most motors can take a lot more than rated for a relatively short period of time. There is no intrinsic reason for a PM motor to be low on torque, provided the magnets haven't gotten weak. A weakening of the magnets will cause the rpm to be higher for a given voltage, and will manifest as low torque and much heating at the same time.

                              If the motor is 'good', my guess is that the controller is not really suitable for it, or hasn't been set up correctly. I've got one of the smaller treadmill motors here, and with 15 volts dc applied, I can barely stop the shaft with my hand. At this point the motor is drawing 4 amps. If I was to raise the voltage to 30, it would draw 8 amps under the same nearly-stalled condition. I would be hard pressed to stall it by hand, if I could at all. That would be more torque than the spindle of my drill press has, being 'geared' down about 4-1 at the speed I normally run it at. I can stall that by hand, so the 1/2 horse motor that runs it is giving less torque than the spindle stall torque- an educated guess is that the motor is giving about what this treadmill motor would be at an 8 amp draw. This small motor would work fine with my drill press, on which I am able to drill 5/8 holes in steel.

                              In part, what I'm suggesting is that your controller should be capable of working at the 8 amp or so level without limiting. I'm guessing that it can't. It's that, or your motor has gone bad.

                              If it's a wound field motor, then it would certainly need the correct controller for that. You could certainly get rpms from it if the field current was weak, but you would get little in the way of torque. You would see a large drop in rpms as you applied even a minor load.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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