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First time poster having some problems with triggering triacs. I'm well aware of the dangers of working with mains voltage and I'm very careful.

I'm using one BT139-800 triac to switch a 35W single-phase motor and one triac for switching 3 ballasts for 6 fluorescent lamps with total power of 108 W. I'm triggering the gate of the BT139 with MOC3063 opto triac. I'm using the circuit below for both loads with the noted resistor and capacitor values.

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The problem I've encountered is that when I connect the circuit to the mains both triacs are already triggered and conducting. I've started debugging by removing the opto triac which did not solve the problem so after that I've tried removing the 360 Ohm resistor between gate and terminal. Obviously the triac did not conduct and I was able to trigger it with carefully shorting the pins with a screwdriver. Thus I figured the problem is in the resistor, but I'm not sure what its value should be. Is there an easy way of determining the correct value? Are there any other problems with the circuit?

Also how do I know that the snubber circuit has correct values? The motor has a 2.5 uF starter capacitor. I guess I could eliminate the snubber circuit for the fluorescent lamps since the ballast has a power factor of 0.98 and the opto triac is zero-crossing. Is that correct?

Cezerb
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  • The other source of trigger is a sudden dV/dt applied across anode cathode, which the snubber ought to attenuate but might not if the PFC has a large input capacitance . – Tony Stewart EE75 Jun 22 '20 at 17:30
  • @TonyStewartSunnyskyguyEE75 I find it unlikely that both triacs (for the lamps and the motor) would encounter this same problem. – Cezerb Jun 22 '20 at 17:44
  • I would not choose such a sensitive gate TRIAC when driven by a low impedance Optoisolated Triac. without a small gate cap. I wonder what layout effects have or Gate Voltage exists? – Tony Stewart EE75 Jun 22 '20 at 18:06

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From the malfunctions you mention, I think you have reversed the A1 and A2 terminals of the Triac. Try swapping them.

Giuseppe Biuso
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