Electronics > Beginners
Problems with triac switching a toroidal tranformer
Sylvi:
Hi
I did not read the whole thread but I think the issue might be fixed easily witha DC blocker. large PTs especially toroidals can become satruated with no load because of asymmetric noise on the mains. Big PTs will growl.
The DC blocker is simply antiparallel high-C electros in parallel with a high-current bridge wired as a bilateral cvoltage clamp. The latter is a cheap way to have antiparallel diodes of high current rating in an easy to deal with package. Do not worry about the electros having up to 1V reverse across them in this application. The higher the PT VA the higher total C required.
There is no need to wire the caps in reverse series in this application. That is unneccesary due to the voltage present, and it cuts the net capacitance in half.
Have fun
SebiTNT:
Thank you again for your answers!
I also really don't think that this is a saturation related issue, because it appears really random and not only when I fire it up with short delays. Please see the video I just made under https://youtu.be/gJdt6XoCtFI
The blue curve is the input voltage and the yellow one is the input current (as before). Please note that the issue only occurs if the triac switches on at the falling edge of the input voltage. Might this be the problem? Of course (as you told me before) one should switch on at Vmax but is this really causing my problem? I am using a circuit for a spot welder (please see the attached picture) and I really don't know how to modify the time when it is switching on.
Circlotron:
I'm thinking maybe the triac gate gets a short pulse every zero crossing of the voltage and seeing the current lags the voltage, the gate pulse should extend from the voltage zero crossing to a little after the current zero crossing. Or better yet, plain continuous DC applied to the gate for as long as the transformer needs to be on.
Interesting also that the fault is only one polarity, so maybe the triac lacks gate sensitivity in one quadrant?
Or maybe the MOC3021 opto is sus?
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