help with 220 volt DC motor

Discussion in 'General Electronics Chat' started by mohamed Sami, Oct 20, 2015.

  1. mohamed Sami

    Thread Starter New Member

    Aug 15, 2015
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    I have a universal motor 220V 1.5A and want to control its speed.
    I made bridge to convert 220V AC to DC and transformer with bridge to get 24V DC.

    I connected it like this image as R3 is the motor and R2,R1 is potentiometer. I used mosfet IRF644.
    Screenshot from 2015-10-20 05:45:30.png
    But the motor works with full speed whenever the potentiometer is even if potentiometer is not connected.
    So how to solve it ?!
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You need to connect both negative sides of the power supply together, problem is as soon as the fet gets enough gate bias it will turn hard on, better to use PWM control for smoother action.
     
  3. mohamed Sami

    Thread Starter New Member

    Aug 15, 2015
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    no change happened the same
     
  4. TheButtonThief

    Active Member

    Feb 26, 2011
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    Where is your motor in the circuit?

    Are you representing it with R3?
     
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  5. pwdixon

    Member

    Oct 11, 2012
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    That FET only has a 20Vmax Vds spec, and the gate voltage limits are +/-5V so you've exceeded that too I'm afraid, it's probably dead by now. OK withdraw all of that now I see you mention a different FET in the text, I was using the one on the schematic.

    But then if you used a bridge from 220Vac to dc then you will get a peak of 220*1.4=308V which exceeds even the IRF644.
     
  6. pwdixon

    Member

    Oct 11, 2012
    488
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    By the way there used to be board rules against posts with rectified mains as it was very dangerous but perhaps they were relaxed in the board rule changes.
     
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  7. recklessrog

    Member

    May 23, 2013
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    The danger still remains though!
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If the motor is indeed a universal motor it would be a lot simpler to power it with AC and use phase-control (i.e. as in a conventional light-dimmer) to vary the speed.
     
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  9. strantor

    AAC Fanatic!

    Oct 3, 2010
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    either your FET has failed shorted, or you've connected it backwards.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    You can change the VR1 and C1 to change the frequency for PWM.
    If you don't like to use zener then you also can use 78L12 to be the voltage regulator.

    220 volt DC motor_mohamed Sami-01_ScottWang.gif

    The mosfet you can choose at least 2 times rating of Vds and 3 time of Id, of course great than more is more better.
    2SK2843_Nch_600V10A_540mΩ_Dc2Dc_Motor_Toshiba.pdf
    FQA19N60_Nch_600V18.5A380mΩ.pdf
    IRFS9N60A-Nch_600V9.2A_0.75Ω.pdf
    NTE2995_Nch_600V10A_±30V_Vgs10V_650mΩ.pdf
    STW-88N65M5_Nch_650V84A-24mΩ.pdf
     
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  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I concur with @Alec_t, Why not use the common way of a Triac on AC?
    In any case you are not going to get accurate speed control without feedback of some kind.
    Max.
     
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  12. ScottWang

    Moderator

    Aug 23, 2012
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    Max :
    Using triac on AC for motor will make noise, I was used that for fan, unless change the frequency, if don't care about the noise that it can be used for that.
     
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  13. mohamed Sami

    Thread Starter New Member

    Aug 15, 2015
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    yes
     
  14. mohamed Sami

    Thread Starter New Member

    Aug 15, 2015
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    i used the one in text IRF644. ok how to get 220 DC ?
     
  15. mohamed Sami

    Thread Starter New Member

    Aug 15, 2015
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    it is universal motor but how to control its speed using arduino ?
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    See Fairchild AN-3006.
    Complete with necessary isolation.
    Max.
     
  17. mohamed Sami

    Thread Starter New Member

    Aug 15, 2015
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    @ScottWang @MaxHeadRoom i will use feedback for sure but how to control speed of universal motor using triac ?
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What type of feedback do you intend?
    Max.
     
  19. mohamed Sami

    Thread Starter New Member

    Aug 15, 2015
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  20. ian field

    Distinguished Member

    Oct 27, 2012
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    Did you check if the MOSFET has failed short circuit? - I'm thinking you'd need at least an IRF8xx to handle the voltage - with all that sparking at the brushes and inductive back emf, even that probably isn't enough.

    Ignoring back emf and any mains transients, the peak value is somewhere near 320V - your MOSFET has to handle at least that, plus a good safety margin.

    Start with a MOSFET that can actually handle the voltage, and protect it from spikes, back emf etc with a MOV.
     
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