Trouble locating 3HP DC motor control.

Discussion in 'General Electronics Chat' started by SytemCore, Nov 13, 2011.

  1. SytemCore

    Thread Starter New Member

    Nov 10, 2011
    5
    0
    I have a DC motor with specs:
    3HP
    90VDC
    RPM 4000
    Duty Continuous
    Rotation CW
    INS. F
    That's all that's on the label. It's in a treadmill, the motor control board has burnt out http://forum.allaboutcircuits.com/showthread.php?t=61884 and I'm looking for a simple motor control to replace it with. I'd like to just hook it up and mount a rheostat, the treadmill is very high quality and I would like to continue using it. When I search for 90V DC motor controls on Ebay and the like, I can only find controllers that handle up to 1.5 HP at 120V. Is it o.k. to use a controller that is rated for half the HP as what the motor is rated at? Can anyone recommend a controller to use with this motor? The diameter of the motor shaft that the belt is connected to is 1 5/8" and it is connected to a 4 inch pulley on the running belt. The max speed of the treadmill is 12 mph. http://s1236.photobucket.com/albums/ff448/systemcore7/
     
  2. pilko

    Active Member

    Dec 8, 2008
    213
    20
    Connect a 12V car battery to the motor (ensure correct polarity). Walk on the belt to check the speed and check the current at the same time.
    From this information you can make a good guess at the amps and volts you need for the max speed you need.
    The controller required to give you the above with a 50% safety margin may be more readilly available and affordable.

    pilko
     
  3. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    P = 3HP * 746W/HP = 2238W
    Iarm = 2238W /90VDC = 25A
    AC Line Current (Irms) ≈ 25A * 1.5 ≈ 37.3A
    Note that this is not including the customary 150% current limit (temporarily overload factor) that is used for acceleration.

    Since 37.3A is absurdly high for a standard 115VAC outlet, it is my observation that the motor was never applied @ full nameplate HP.

    Working the numbers backwards from a 20A outlet, the max HP works out to 1.5HP. Note that 1.5HP is the largest 90VDC control commercially available for 115VAC--and that is likely to be a 20A circuit breaker popper when the drive current limits--30A branch and high current connector required for industrial application.

    Go with the 1.5HP drive control!
    You will find the industrial control to be far more rugged.
    Post a photo of your burned out control.

    Now working the max speed:

    Shaft Speed = 4000R/M * M /60S = 66.7R/S
    Geared speed = 66.7 * 1.625" /4" = 27R/S
    Belt Speed = 27R/S * 4" * '/12" * ∏ = 28.3 '/sec = 19.3MPH

    Actual Max Motor Shaft Speed = 4000R/M * 12MPH /19.3MPH = 2487R/M
    Actual Max Armature Voltage = 90V * 12 /19.3 = 56V

    It appears that you will have to turn the max speed pot on the speed control down substantially--it may not adjust down that far--at any rate, the speed pot will adjust down to zero OK. Also, turn down the current limit to keep from tripping the breaker. Set the IR Comp pot to 0% (tight speed regulation not required). Set the Min Speed to whatever you desire.
     
    Last edited: Nov 14, 2011
  4. SytemCore

    Thread Starter New Member

    Nov 10, 2011
    5
    0
    I'll order the 1.5HP industrial control and here are photos of the burned out board. http://s1236.photobucket.com/albums/ff448/systemcore7/ I would like to repair this at some point, it looks like the bottom of the board is somewhat burnt at one of the solder joints for the UF1004FCT rectifier. Can anyone tell me what rectifier would be a good replacement for this one (I can only find datasheets for it), and if by looking at the photos what else I should try replacing?
     
  5. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Hey the photos show a PWM drive--my calculations were for a SCR drive--the PWM topology offers lower line current at low speeds than the SCR topology--at high speeds, things are not much different. For practical purposes, there should not be much difference except for the slight hum of the 120hZ current ripple with the SCR topology. What type of drive control were you looking to buy?
     
  6. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    This rectifier is a dual-diode with the center lead the cathode--I doubt that it is applied as such and suspect that the two outside leads are connected thus paralleling both diodes--check this on the artwork. If so, use this single junction device that is available from DigiKey--the pin-out is compatible for replacing paralleled dual diode devices:
    http://search.digikey.com/us/en/products/RFUS20TM4S/RFUS20TM4S-ND/2615650
    I could not find a dual diode with a 400V rating.

    On the IGBT, I recommend:
    http://search.digikey.com/us/en/products/IRG4PC40FPBF/IRG4PC40FPBF-ND/811595

    On the bridge rectifier, I recommend:
    http://search.digikey.com/us/en/products/GBPC3506W-G/641-1384-ND/2074849
    This can be checked with a ohmmeter to see if it is shorted--will blow line fuse if it fails

    Happy Jogging
     
  7. SytemCore

    Thread Starter New Member

    Nov 10, 2011
    5
    0
    Here is one of the controllers that I found, would this do the trick? http://www.ebay.com/itm/Fincor-2230...293?pt=LH_DefaultDomain_0&hash=item3ef9897fd5


    I just ordered the devices from DigiKey, thank you for looking them up for me.
     
  8. SytemCore

    Thread Starter New Member

    Nov 10, 2011
    5
    0
    I replaced the IGBT and rectifier, the bridge rectifier tested good so I left it. The treadmill started to run at 1mph, it ran at 2mph but when I hit the 3 mph button, sparks flew and there was smoke. Any ideas about what to try next? I bought several of each device.
     
  9. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    I honestly do not know what to think on that one as it is difficult to troubleshoot something like that under these conditions. Impressed that it ran at all...
     
  10. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,004
    1,525
    How are the brushes in the motor? If worn or bad, they can cause high resistance and extra load to the controller.
     
  11. pilko

    Active Member

    Dec 8, 2008
    213
    20
    Do what I asked you to do in post #3 and report your amps and approx % belt speed. I then maybe able to spec. you a sensible economical controller.

    pilko
     
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