flickering with inductive load

[BYY]

hi.. i m using zero crossing optocoupler to trigger triacs which are then connected to transformer tappings... triacs are switched accordingly and gives transformer output 220 all the time.... when resistive load is connected with transformer results are ok but when inductive load(motor) is connected it flickers.. can any body comment what could be the reason??

 

[FvM]

With inductive load, the current zero crossing is delayed related to voltage zero crossing. Without an effective snubber circuit, the voltage across the triac and opto triac will rise too fast for reliable triggering, so the circuit triggers accidentally. At worst case, you get a DC voltage at the transformer with a risk of damaging either triac or transformer or at least blowing a fuse.

I won't use zero crossing opto coupler with inductive loads. It should be noted in addition, that to avoid saturation of transformers and other inductice AC loads, you would want to switch the triac at peak voltage rather than zero crossing.

 

[BYY]

is there any way to get rid of flickering with zero crossing??

---------- Post added at 08:48 ---------- Previous post was at 08:47 ----------

power factor could be the reason in this case??

 

[FvM]

As said, use sufficient snubbers. Particularly a circuit where the voltage for the opto triac is filtered by a capacitor, like this https://www.edaboard.com/threads/162207/#post686270

 

[BYY]

yeah i have already used calculated snubber but problem still persists for an inductive load....