Phase Angle Control Using Controller

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gauravkothari23

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Hi all.
I am trying to Control the Speed of 120W AC Motor using controller NUC029LAN, Traic BT136, Zero Detection Circuit.
Have also attached the circuit diagram and some wave form. In the waveform i am triggering the Triac after 7ms delay after zero crossing is detected.
my problem is when incandescent bulb is connected as load, it works perfectly (wave form attached at 7ms of delay).
But when 120W AC motor is connected, i am not able to control the speed, it rotates at full speed only. (Wave form Attached at 7ms of Delay).
The waveform when motor is connected, is completely changed.
Have also attached the waveform of MCU Pin which is driving the Triac with reference of 12V AC, just for reference to confirm that there is no issue with the software part.
Can anybody please let me know where the issue is.
 

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i have already uploaded the circuit in post 1
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have even tried adding snubber to MOC3021, but the things are not yet working
 

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there is no way to debug your circuit ( or likely buggy software ) with such little and incomplete information.
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Triac speed-control circuit for induction motors

Electric Motors -- Fundamentals and Control
www.industrial-electronics.com
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Last edited:

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Hi all.
Finally Done with it.
Now i am able to control the speed of the motor. and motor runs very smoothly in any speed which is required.
Thanks to all for your support.
 

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Hi,
Remember "ELI the ICE man?"
This tells us that in an inductive circuit, voltage leads current. So even when the voltage has gone down to zero, the current has not. It takes some time before the current gets down to zero after the current has. In a purely inductive circuit, it takes 90 degrees.
Also, when the voltage starts to rise from zero, current doesn't start until after a certain phase angle depending on the RCL combination of the circuit.

You need to know your motor in order to determine the time when the triac is in the proper quadrant and when the motor current is sufficiently large so you can trigger the triac.
 
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