2 kW motor speed controller

Discussion in 'The Projects Forum' started by darsie, Mar 13, 2014.

  1. darsie

    Thread Starter New Member

    Feb 19, 2010
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    Hi!

    My flat mate bought a defective treadmill cheaply and has now bought several motor controllers from other treadmills, struggling to figure out how to connect/drive them. I suggested building a controller but he's reluctant as his electronics fu is rather small (yet).

    What do you think about this PWM scheme?

    [​IMG]

    The capacitor shall avoid 50 Hz hum in the motor. The inductor shall avoid current transients in the transistor. Also there will not be a current transient through the rectifier to the capacitor when the thing is plugged in.

    Thx, Bernhard
     
    Last edited: Mar 13, 2014
  2. darsie

    Thread Starter New Member

    Feb 19, 2010
    15
    0
    Ahh, the diode should span the motor and the inductor.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    760
    A transistor as a power switch. That won't do.

    Get a MOSFET or an IGBT

    Next thread motor needs a steady DC. That is mains rectified smooth DC. The power switch will control the motor.

    And this thread will get locked soon if you plan to do what you drew.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Yikes ! 2KW on a thread mill ?
    Are u sure ?
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Instead of buying controllers out of T.M.'s he should have looked for a KB/Baldor DC controller, many come up on ebay.
    They have SCR bridge versions or (better) PWM tyes.
    Max.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Don't be fooled, if you compare the frame size of 2-2.5Kw motors out of T.M.'s with industrial DC motor of the same HP you can see the difference!
    Max.
     
  7. darsie

    Thread Starter New Member

    Feb 19, 2010
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    0
    I just drew the (incomplete) transistor symbol as I hadn't decided what switch to use. Hmm, not sure if a suitable MOSFET can be driven with an avr microcontroller output. Perhaps if the switching frequency isn't too high. Maybe 20+ kHz to get out of audible.

    Anything wrong with the smoothing capacitor I drew?

    Here's an updated circuit:

    [​IMG]

    Do you think a 400V transistor will do?

    So, the general scheme is ok?

    He says, it's 2 1/2 HP, which is 1839 W.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    PicMicro claim that is only necessary to go as high as 4Khz PWM with motor circuits above this there is little audible difference, so they claim.
    You can either get Mosfet driver IC's or use a logic level Mosfet Gate.
    Max.
     
  9. strantor

    AAC Fanatic!

    Oct 3, 2010
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    IGBT or MOSFET would definitely be better, but a transistor could be and has been used. The older VFDs had darlingtons in them.

    You probably know more specifically about the treadmill motor than I do, but would have thought that it's not too picky about input power. DC drives (other than PWM) for industrial DC motors usually have SCR output with no filter caps. They just phase angle fire rectified AC into the motor. The motor is pretty stupid and doesn't know the difference. Perhaps treadmill motors are more picky?
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    T.M.'s are pretty basic, I have used them with both SCR full-bridge controllers or PWM, the SCR's are a bit noisier, especially at low rpm, the PWM give a little more top end RPM due to the higher DC level.
    This is why T.M. controllers are typically PWM.
    Max.
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Mostly TM motors run at full speed around 180V to 200V DC.
    For smooth speed at low RPM, there should be feedback.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Most do, in the form of a slotted opto sensor.
    Max.
     
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