AC Motor Speed Controller

Discussion in 'General Electronics Chat' started by hazim, May 27, 2010.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Hello
    A friend asked me to help him in building a speed controller circuit for a 220V 0.6A AC motor which is to be used in his BS senior project (Mechanical Engineering).
    I'm not familiar with power AC electronics, but I found this circuit and seems to be easy..
    [​IMG]

    The circuit with some details http://www.aaroncake.net/circuits/acmotcon.asp

    U1 is a DIAC Opto-Isolator, they are not available in my country.. I'm thinking if it works if I make one using a white bright LED and a DIAC in series with a photoresistor (facing the LED), and putting them in a small dim case. Is there any other solution?:rolleyes:

    Another question.. in the parts list they say R13 is a 47 Ohm 1W Resistor, and that larger loads will require a smaller value.
    If the motor is rated 0.6A, I see the real current will be more than that when there is a mechanical load (blades/fan in this case) and I assume for now the current would be about 1A. And as it's clear from the circuit, the voltage across this resistor will be used to voltage supply a part of the circuit..

    Since the load current is about 1A, I see R13 should be about 20Ω 50W resistor (20Ω x 1^2 = 20W...). The voltage drop across the resistor will lower the load voltage a little(comparatively), but it is ok.
    Also, if 20Ω resistor will be used, the voltage across it will be around 20V which will not require a transformer? right?

    Regards,
    Hazim
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    One thing I can tell you is that u cannot make an opto.
    It has zero crossing too. So you got to find that part first
     
  3. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I can't find it.. and so I'll look for another circuit or idea. What about a 220V primary 220V-180V-140V-100V-60V secondary with a appropriate switch?:)
    It is much expensive.. and heavy.
     
  4. R!f@@

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    What type of motor is it.
    Post the part no. or a photo.
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    R13 doesn't really provide part of the power for operation. It is the current sense device. The voltage developed across it is directly proportional to the current through the motor. The transformer steps this voltage down. The result is then rectified and filtered to provide a DC component that adjusts the emitter bias on Q1 Higher current will tend to lower Q1 current and ultimately reduce the angle of conduction of the triac.
     
  6. R!f@@

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    T1 purpose is to isolate the control from power side, R13 is the current sensor and these components provide feedback from the looks of it.
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Why is the is this thread for a mains-powered device without appropriate transformer isolation still open?

    John
     
  8. R!f@@

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    Apr 2, 2009
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    since the OP have a circuit and is thinking of building it, then locking the thread won't stop him from killing himself :D.
    heheheh..I think he knows the risk. still no one is suggesting to build it yet
     
  9. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    It's more probably not an inductive motor. I'll make sure.
    I found opto-isolated diacs, they named them "optocoupler triacs". Here are the available ones:
    http://www.ekt2.com/ekt/prodList.as...trSearchCat=0&curPage=1&sortField=description

    I'm not sure which one fits my need in the circuit, the triac I will use is AC05F (600V 5A IGT<10mA) or equivalent.

    R13, the current through it is the same as the motor current right? if yes then 1A^2 x 47Ω is about 50W, they say R13 is a 47Ω 1W resistor... What to do with this?
    Transformer isolation?:)
    Regards,
    Hazim
     
    Last edited: May 27, 2010
  10. R!f@@

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    Apr 2, 2009
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    Hmm that opto is perfect

    As for R13.. are you misreading it....I think it is 0.47Ω.
    A huge resistor in series with motor is a crazy idea
     
  11. BillB3857

    Senior Member

    Feb 28, 2009
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    I just re-read the info on the link in the original post. UNIVERSAL MOTORS! Brush type required! This circuit should not be used on induction motors.
     
  12. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    No I'm not misreading it.. in the part list it's written "47 Ohm 1W Resistor". Maybe they made the mistake.
     
  13. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Yes, I edited my previous post about the motor (there was a missing word about the motor type...). I know AC brush type motors speed controlling depend on phase angle as this circuit doem while induction motors speed controlling depend on the frequency...
     
  14. jpanhalt

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    Jan 18, 2008
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    It has been stated many times that such circuits are inherently dangerous. There has been some discussion about knowledgeable OP's being somehow exempted, which I hope no one took seriously. Nevertheless, this OP doesn't seem even to know what type of motor s/he has.

    John
     
  15. R!f@@

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    I agree with john
     
  16. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I don't have the motor, I mentioned in the first post that I'll build this circuit for a friend.. he have the motor, I didn't see it and I can't now, but it's more probably a normal brushed AC motor, I'll make sure.

    I'm a BS electronics engineering graduate and I work with electronics and electricity from I was 10 years old. I have repaired abundant electrical/electronic appliances... so relax:)
     
  17. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    The degree makes no difference, if you don't know. Control of any motor begins with knowing what type of motor you have.

    It is a safety issue and this matter has been discussed here numerous times. You must also consider that not only do people with experience and training have access to this site, so do 10-year-olds and others with no experience.

    Why not find out what type of motor you are trying to control and begin a new discussion on the right foot?

    John
     
  18. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    It's a 220V 0.6A brushed AC motor;).
    You are right to be concerned.. Thanks.
     
  19. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I still have one final inquiry. Will a MOC3010 optocoupler triac work? the datasheet says that it's a "NON-ZERO-CROSSING TRIAC". I bought it (1$)
    If it must be a zero crossing type, then I'll buy one (MOC3040)..
     
  20. R!f@@

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    zero crossing is not compulsory but will eliminate surge currents. So it is a sort of an improvement and the opto is not a triac but rather an isolation driver specifically designed to drive triacs
     
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