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  • DC Motor Actual HP

    I am replacing a 2 speed 3ph motor 575 volt 1.5/1 hp 3410/1700 rpm with 2hp DC Treadmill Motor 5120 rpm that speed will slowed down with A series V belt with Max rpm at 3400.Also using a 4" Variable Speed Sheave on DC motor and 6" pulley on Drill Press,this will give a good speed variance with mechanical and electronic speed control on motor.It's a Modig Radial Drill with 6 speed gear reduction.

    In the pic shows motor rating at 5.10 HP Peak, how is this possible?
    You may only view thumbnails in this gallery. This gallery has 1 photos.
    Last edited by Tundra Twin Track; 11-30-2019, 11:52 PM.

  • #2
    Motor HP ratings are usually continuous duty (24/7) or intermittent duty (which may be 10-30 minutes on and a similar time off). Generally a motor (or transformer) can supply 140% of continuous rating at 50% duty cycle. Motors can typically supply 3-4 times nominal power for short durations. This is mostly due to thermal limitations and temperature rating of insulation. There is also a maximum torque limitation beyond which a motor will stall. You can also apply higher voltage to get higher RPM and power, but there are limitations due to maximum safe speed and deterioration of brushes and commutator.
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

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    • #3
      There's also the old "Sear's horsepower" gimmick: the locked-rotor current (maximum motor will draw) times the rated voltage divided by 746. Leeson is probably more trustworthy than some Chindium no-name, but you never know. Especially one pulled from a treadmill.

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      • #4
        Name plate voltage of 102 is a bit strange, but nominal 18amps would give you 2.46 HP electrical input. What sort of power supply are you using?
        Motor RPM will be directly related to input voltage, so presumably the 5100 rpm rating is at the 102 VDC input. I suspect the 5.10 peak is locked
        rotor rating.
        Last edited by sch; 12-01-2019, 04:20 PM.
        Steve

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        • #5
          DC motors typically have two manuf. rating curves, the continuous torque rating, which is generally maximum at zero rpm, and gradually slopes down to the maximum rpm rating.
          There is a also a peak torque rating which can be entered momentarily, any length of time in this area can result in motor destruction.
          Max.

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          • #6
            Torque is essentially current, so more torque is more current.

            On overload, the motor will pull more current when it slows down under load, so then the torque increases, presumably faster than the speed decreases, leading to an increase of power. But the current heats according to current squared, so the heating is 4x at 2x current. Cooling is not improved much, and probably decreases due to lower speed, so those ratings are short term.

            The voltage drop across the motor is largely due to back EMF, only around 10% of it is due to resistance. So it does not take a lot more voltage drop to increase the current a lot. Back EMF is related to RPM, and RPM can drop a few percent without much effect on operation.
            Last edited by J Tiers; 12-01-2019, 04:54 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......

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            • #7
              I am powering it with Black Box that I got off ebay a few years back,I'm now thinking of just using the Poly Belt and reducing speed by pulley rather than the Variable sheave.In theory the slowest it should have run is half speed the Modig has 8 speeds with the original 3410/1700 so 4 different gear speeds.

              I was curious with Real HP compared to the 1.5/1 hp 3 ph motor as been mention on numerous posts in the past that DC treadmill motors are small ponies compared to AC motors.


              I'm electrically challenged so really appreciate the feedback.

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              • #8
                Originally posted by Tundra Twin Track View Post
                I am powering it with Black Box that I got off ebay a few years back,
                .
                DC motors have a smaller frame size for a equal HP in general.
                The 'Black Box' may be just a bridge and Triac controller, which offers minimum control.
                If you use one of the T.M. PWM controllers these generally have built in ramp up and current feedback control/protection etc.
                Max.

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                • #9
                  Treadmill motors are typically label-rated for 'treadmill duty':
                  Treadmill motor energy is measured in horsepower (HP) and can be sorted into three different rating systems:

                  1. Peak Duty: Generally the weakest. “Peak” stands for the peak horsepower that the treadmill will reach and no more.
                  2. Treadmill Duty: In-between peak and continuous
                  3. Continuous Duty: The highest rank. The number associated will describe how much power is maintained throughout the workout.
                  Southwest Utah

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                  • #10
                    One Nordic Track treadmill was labeled as 5 HP. The 3 phase AC motor would develop 5 HP when run at 380V @ 200 Hz. The inverter installed in the machine was powered from a 120 V cord and was rated at about 1000W. So in the treadmill it developed no more than 1.5 hp at most.
                    North Central Arkansas

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                    • #11
                      That interesting are Hz normally around 50-60 , hope to have Drill running today will see if it works.

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                      • #12
                        I'd go with polyV for sure, but if you're going to do alot of low speed work you'll need to work out the gearing/ ratios so that the lowest speed you'll want is at least 1/3 of the rated motor speed. Might need a jack shaft to do so. Torque falls off quite a bit at low speeds with those treadmill motors. The variable sheeve thing is a pretty neat idea, I wouldn't dismiss that too readily. All of my treadmill motor conversions have at least 3 pulley ratios. I usually just leave them set in 1 ratio and vary speed with the controller, but every so often I'll need the next ratio up or down. Like using a 1" S&D drill on some stainless on my mill - worked ok on the lowest speed ratio at ~60 or 80rpm. Really small end mills (1/16 and the like) use the high ratio to get speeds up to 3000rpm or so.

                        As for treadmill HP, a handy rule of thumb is that continuous HP is ~2/3 of nameplate. Is your Blackbox one of those KB all in one units? Those are pretty neat if so, takes alot of work out of the conversion.

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                        • #13
                          Originally posted by mattthemuppet View Post
                          I'd go with polyV for sure, but if you're going to do alot of low speed work you'll need to work out the gearing/ ratios so that the lowest speed you'll want is at least 1/3 of the rated motor speed. Might need a jack shaft to do so. Torque falls off quite a bit at low speeds with those treadmill motors. The variable sheeve thing is a pretty neat idea, I wouldn't dismiss that too readily. All of my treadmill motor conversions have at least 3 pulley ratios. I usually just leave them set in 1 ratio and vary speed with the controller, but every so often I'll need the next ratio up or down. Like using a 1" S&D drill on some stainless on my mill - worked ok on the lowest speed ratio at ~60 or 80rpm. Really small end mills (1/16 and the like) use the high ratio to get speeds up to 3000rpm or so.

                          As for treadmill HP, a handy rule of thumb is that continuous HP is ~2/3 of nameplate. Is your Blackbox one of those KB all in one units? Those are pretty neat if so, takes alot of work out of the conversion.
                          I changed my Idea again and am Flange mounting direct coupled with different motor 2.25 hp 3200 rpm.Will post pics of it later today if I get up and running.
                          This Modig Radial Drill is gearhead so hope it works out.

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                          • #14
                            ... you have *no* idea how much this reminds me of the 6.5 HP shop vacs at Home Depot.

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                            • #15
                              Originally posted by mattthemuppet View Post
                              Torque falls off quite a bit at low speeds with those treadmill motors. .
                              Matt, the reason for that would normally be the result of conditions in the controller than the motor, The vast majority of PM DC/BLDC motors possess maximum torque at zero rpm.

                              https://www.youtube.com/watch?v=pxtRlKs0pAg
                              Max.
                              Last edited by MaxHeadRoom; 12-10-2019, 04:40 PM.

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