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[SOLVED] A little problem in TRIAC phase control

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nimeshasilva

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I have made a digital dimmer as mentioned in the on semiconductor app note AND0811/D and my purpose is to control a single phase split capacitor motor. and when I connect it to a motor the oscilloscope the waveform is like as shown in MoT.jpg in the attachment. and then i disconnect the motor and connect a light bulb and the waveform as shown in LAMP.jpg in attachment. I didn't connect any noise filter for the system.

can you guys tell me that is this waveforms are normal or erroneous??
is there any harmonics coming when driving the motor?? and if, can anyone suggest me a schematic for filter-out the harmonics??

Thank you.. :)
 

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    MoT.JPG
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  • LAMP.JPG
    LAMP.JPG
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can you guys tell me that is this waveforms are normal or erroneous??
basically normal operation. I don't think, that the simple circuit is particularly designed for inductive loads. You may face unintended behaviour, including halfwave output at high phase angle settings. In this case, there's a risk to overload the motor.
is there any harmonics coming when driving the motor??
Phase angle control is genrating a lot of harmonics by design.
and if, can anyone suggest me a schematic for filter-out the harmonics??
That's rarely feasible with acceptable effort. Usually, LC "noise" filters are needed with dimmers to keep the EMC rules, but they can't remove the low frequency harmonics.
 
Thanx for quick reply FvM.
halfwave output at high phase angle settings.
ya, I got halfwave output and modified the circuit to avoid it. :) and used a good snubber, a varistor and a high dV/dt capable TRIAC to get the inductive load handling capability. is there anything more I should be taken into account in the inductive load case??
 

Seems like if Neutral is floating.
Check it, or just to test, connect to Earth.
 
Thanx Guys., :)

Seems like if Neutral is floating.

No andre, Neutral is connected to load in both cases. and when the neutral is connected to earth, the trip switch is activated instantly.

And just one thing I need to know, How do I measure harmonics, where should I connect the oscilloscope probe to see the harmonics, I mean should I connect osc. probes to motor end or power supply end??

Thanx
 

Seems like if Neutral is floating
You're referring to the sine voltage visible in off state? I guess, tt's either motor EMF or the voltage drop caused by the snubber leakage current (with a light load).

How do I measure harmonics?
At the power supply end, you hardly won't see harmonic voltage distortions caused by the triac load. You are already measuring the motor side and see the distorted waveform. To determine the distortion power factor, the current harmonics are measured.
 
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