DC motor driver

Discussion in 'The Projects Forum' started by borislavKI, Aug 1, 2013.

  1. borislavKI

    Thread Starter New Member

    May 26, 2013
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    Hi everyone.

    IM SORRY FOR MY BAD ENGLISH I HOPE YOU WILL UNDERSTAND ME:D

    Im working to build a sawdust burner for home central heating.
    I need to control speed of air supllying fan with PWM signal that comes from PLC output.
    i need help to build driver for fan motor, shematics, circuits, instructions anything.

    PWM signal : 24V 500Hz duty cycle from 30% to 100%
    Motor: 12V DC 10A brushead motor

    If possible, i want to isolate PLC output with optocoupler.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    Do you have the 12VDC power supply already?

    You need a MOSFET, that will accept the PLC signal (after isolation and inverting) and control the large current through the motor. The isolator will invert the PWM signal from the PLC and you'll need another small transistor to restore the right sense. You will need a resistor to limit the current through the LED of the optoisolator.

    After all that you will apply the signal to the gate of the MOSFET. Source to 12VDC ground, drain to motor. Motor connected to +12VDC. So the MOSFET switch completes the path to ground for current through the motor. You'll want a reverse biased diode across the motor to absorb back-emf.

    Choose a MOSFET rated to at least about ~4X the 10A continuous current. It adds little to the cost to over-specify a MOSFET.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    If you want maximum rpm from your motor, the recommended P.S. voltage for the likes of PWM control is at least motor voltage + 10%.
    Not super critical.
    Max.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    That reminds me that the transistor in the isolator could likely be configured as an emitter-follower and used to directly control the gate of the MOSFET, eliminating the extra inverting transistor. There should be plenty of voltage available even for a normal n-type MOSFET. You would use a pull-down resistor, say 1KΩ, on the gate.

    I use the IRF540N for common tasks like this and I think it would be an option here. But I'd get something more modern if I didn't already have a bunch of them.
     
  5. borislavKI

    Thread Starter New Member

    May 26, 2013
    4
    0
    [​IMG]

    Something like this?

    I have few IRF1010N mosfets and CNY17 optoisolators.
    Can i use them?
     
  6. donpetru

    Active Member

    Nov 14, 2008
    186
    25
    I have not looked in the CNY17 datasheet, but I think, in the above scheme, the voltage between the collector and emitter of the optoisolator is too high.
     
  7. borislavKI

    Thread Starter New Member

    May 26, 2013
    4
    0
    For CNY17 Collector-Emitter Breakdown Voltage BVCEO 70V
     
  8. donpetru

    Active Member

    Nov 14, 2008
    186
    25
    BVCEO is OK but the collector of the transistor CNY17 should have connected a resistance to limit the current through the optoisolator. Moreover, in parallel with the grid-source junction MOSFET should connect a Zener diode to protect the transistor grid's surge.
     
  9. borislavKI

    Thread Starter New Member

    May 26, 2013
    4
    0
    Can you draw me schematics?
     
  10. donpetru

    Active Member

    Nov 14, 2008
    186
    25
    Try to use a P-channel MOSFET transistor as shown below.
     
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