| Electronics > Beginners |
| Problems with triac switching a toroidal tranformer |
| (1/4) > >> |
| SebiTNT:
Merry Christmas everyone! I have a BTA100-800 triac (actually it is a Chinese spot welding controller) which is used to switch a toroidal transformer on for a few cycles. My input voltage is 230 V. If everything is well, I get a nice sine wave output from the transformer with a loaded (almost shorted) secondary winding. My problem is, that (with nothing changed) for most of the time the output looks like crap (like on the second picture) and I have no clue what is causing it. There is a snubber circuit already connected over the triac consisting of 10 nF cap and about 47 Ohm resistor. Additionally I have connected one 1 uF capacitor in parallel to the transformer, because at first I had problems with the triac not shutting off the current under load (probably because of a too high di/dt). This problem has gone after connecting the 1 uF cap but the problem with often getting crap on the transformer's output is persistent. It would be great if someone could give me a hint. Thank you all in advance! Sebi Edit: (hopefully :-) removed typos |
| Benta:
What you probably have is a toroid in deep saturation. This gives unpredictable output voltages when loaded. The trick is to use the Triac to switch on the primary at maximum mains voltage, or just after. It would be interesting to see your input current, not just the voltage, and also the unloaded output voltage. . |
| Gyro:
Yes, that looks like saturation from switching on at the wrong part of the cycle. Switch on at mains peak as Benta says... and also switch an equal number of positive and negative half cycles. You're going to need to add intelligent mains cycle / zero crossing detection to make it reliable I'm afraid. |
| not1xor1:
--- Quote from: Gyro on December 25, 2018, 08:36:47 pm ---Yes, that looks like saturation from switching on at the wrong part of the cycle. Switch on at mains peak as Benta says... and also switch an equal number of positive and negative half cycles. You're going to need to add intelligent mains cycle / zero crossing detection to make it reliable I'm afraid. --- End quote --- the OP could use this nice trick to switch the triac on close to the peak of the AC voltage (image originally posted by BravoV) |
| SebiTNT:
I finally had the time to make the requested input current measurements. Please find these attached. Is this really a saturation related issue? Sometimes I'm getting a "normal" sinewave output and sometimes not. Wont't the transformer be saturated every time? Edit: For me it looks like something is rectifying the input current. |
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