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DC Motor Actual HP

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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?
    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.
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030


    • #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.


      • #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.


        • #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.


          • #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.

            Keep eye on ball.
            Hashim Khan


            • #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.


              • #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.


                • #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.