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help required on ac motor speed control

Discussion in 'Sensors and Actuators' started by sherazi, Mar 8, 2010.

  1. sherazi

    sherazi

    91
    0
    Mar 8, 2010
    the mtr is attached to microcontroller.. what would be the best idea to control the speed? whether to do that in programing using a triac and to set the duty cycle by programing....

    or

    some hardware type .. do help
     
  2. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    The motor... What motor? What are you trying to do with the motor? What power level?
     
  3. sherazi

    sherazi

    91
    0
    Mar 8, 2010
    Ac motor speed control

    regards..

    i am using Micro Controller to control the speed of an ac motor (2amps), how can i control its speed?...

    i have tried triac, switching, but that doesn't affectively change the speed, the mtr sound changes but speed remains almost the same...

    is there a better way or is there any problem in the duty cycle...

    what could be the best idea to control the speed...



    i would be using it for gate opener so i need it to slow down when its near to fully open or fully close... i want that it should really slow down
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    Ac motor speed control

    Can you identify what type of motor it is? There are different types of AC motors and some are far more difficult to slow down than others.
     
  5. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    That sounds like an asynchronous motor. They are not the easiest to control.
    The best option is using a Variable Frequency Drive, but they are costly I guess.
    Some other (commercial) special triac "dimmers" are made to control these types of motors and would not cost much more than an ordinary dimmer.
    I once found a diagram on the net for a triac speed regulator that worked by omitting cycles from the mains, thereby allowing full speed, half speed, one third speed, and so on. I'll try to see if I can find it again.
     
  6. sherazi

    sherazi

    91
    0
    Mar 8, 2010
    cant i use the moc 30 series which drives a triac and the duty cycle being set by microcontroller

    as far as i think it would be better to make it turn on and off... but would there be adverse effect on motor of this?... or is it practicle
     
    Last edited by a moderator: Mar 15, 2010
  7. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Ah, yes, if you have a fast microcontroller, that could be used provided you are able to synchronize the uc duty cycle to the mains cycles.
    The triac may need a constant - or repeated - trigger pulses during the whole half-cycles due to the motor's inductive nature that might otherwise turn off the triac before each cycle is completed.
    I was mistaken in my previous post; the motor can only be run at full, 1/3rd, 1/5th, 1/7th speed and so on.
    The way the motor needs to be powered for 1/3rd speed is; apply one positive half-cycle, wait one full cycle, apply one negative half-cycle, wait one full cycle, repeat.
    For 1/5th speed you wait two full cycles between each half-cycle applied.
    This will be a more even and effective speed control than turning it on & off with full cycles.
    The motor needs to have a positive half-cycle followed by a negative one and vise versa. Never apply two positives w/o a negative in between, that will effectively make a high DC voltage with corresponding current spiking.
    Apart from that, either way you control it the motor will not be adversely affected.
     
  8. sherazi

    sherazi

    91
    0
    Mar 8, 2010
    it seems to be a tough task for me.... and what if the motor is synchronus

    how can i differentiate b/w the two types...of ac motors...........

    i think i have a 1 that can be controlled through triac using the avr atmega8... its for sliding gate opner... the motor is hercules 500 from stagnoli...

    now can u help
     
    Last edited by a moderator: Mar 15, 2010
  9. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    I know only little about programming, you might try to ask for help in Microcontrollers and Programming, providing as much information about the whole system as you can.

    Synchronous motors are "never" used for this kind of application and are "never" as large as you need. Even if it was it could still be controlled in the same manner.
    Your motor needs to be reversed however. I guees that is taken care of by changing windings with a relay. Post the "label" on it if you already have the motor available.
     
  10. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Yes, I found that on the net but it doesn't tell me much. I'd need to know about the internals, either good pictures or a good description.
     
  11. sherazi

    sherazi

    91
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    Mar 8, 2010
    doesnt the pdf and pic provide help... it has 3 wire coming out of it has a capacitor

    what do i have to describe??
     

    Attached Files:

    Last edited by a moderator: Mar 15, 2010
  12. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Thanks, that label tells me it's a capacitor run asynch motor, just as I'd expect. It's good.
    Ok, how about the connectors in the box (for the outside cable), what are their labels?
     
  13. sherazi

    sherazi

    91
    0
    Mar 8, 2010
    THERE ARE NO LABELS...
    I THINK ITS ASYNCHRONUS...
    OK NOW HOW CAN WE CONTROL ITS SPEED...
     
    Last edited by a moderator: Mar 15, 2010
  14. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Yes yes, we already established that it's an asynchronous capacitor run motor, or a permanent split capacitor (PSC) AC induction motor in other words.

    Check out this document and see if there's anything you can use.

    You will be needing to know what the connectors in the box are for, if you are going to hook it up for real..
     
  15. sherazi

    sherazi

    91
    0
    Mar 8, 2010
    ohh thats really helpfulll............ thanx alot.... so as in this can i just ignore the zero crosssing and try on for several cycles and on for several cycles... for the triac...

    if i use the phase control... thts firing the triac at a certain instant of every cycle ... how can i synchronize with the mains zero crossing
     
  16. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    You won't be using phase control, only on & off, and the "retries" needs to be within each cycle.

    Btw.: If you're going to have any chance of getting help in the Microcontrollers forum you'll have to establish what kind of controller you will be using.
     
  17. sherazi

    sherazi

    91
    0
    Mar 8, 2010
    cant understand that...

    if i use on and off and that even suppose to create 50% duty cycle... i might make it on for 5 pulses and off for five pulses without considering the zero crossing...

    would this work...
     
  18. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Retries=retrig's, look at the gate signal in beginning of the document.
    But never mind that..
    A random phased duty cycle may, as I stated earlier, lead to current spiking.
    Yet you may wery well do it and get away with it. If fuses and/or triacs doesn't blow then the motor will be regulated.
    One trick to prevent current spiking from happening is to make sure the off period is always at least half a second - preferably one second.
    Now maybe you can do some research and tell me why that is so..
     
  19. sherazi

    sherazi

    91
    0
    Mar 8, 2010
    sorry but couldnt get the ans... can u help as usual
     
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