guys, I tried to make an SSR for my window Air conditioner 2 Tonnes "2.5kW" the problem the Triacs get damaged instantly I tried 4 Triacs so far 2 BTA41 and 2 BTA24 I tried different circuits, I'm suspecting the Triacs to be counterfeited or something because I calculated the current to the compressor it was around 11A@240V and those Triacs can handle 41A and 24A. I mean by damaged that they fail closed, they will not turn-off even if I cut the DC from the Opto-isolator and when I checked the terminals there was continuity between MT1 and MT2.

The circuits I tried so far enter image description here

I know it's better to use contactors with AC but they are so bulky and need transformer and a big one 4A@24V to control them.

Is the problem with my parts or I'm missing something? PS: The resistors are 1W, The Opto-Isolator is MOC3063.

  • \$\begingroup\$ What do you reckon the starting current is for the motor(s)? x 2? x 5? x 10? \$\endgroup\$
    – Transistor
    Mar 18, 2020 at 22:41
  • \$\begingroup\$ Are they on a decent heatsink. Power dissipation will be very high. \$\endgroup\$
    – elchambro
    Mar 19, 2020 at 1:26
  • \$\begingroup\$ Try a 1 kW heater as test load. About 4A at 230V - but no surge current on turn on. Then if OK try some incandescent bulbs. They have start surge. Start with eg 1 x 100W bulb and work up. How many 100W bulbs can you drive safely? \$\endgroup\$
    – Russell McMahon
    Mar 19, 2020 at 7:19
  • \$\begingroup\$ @elchambro Yes there is a heatsink I custom made it myself from Aluminium and the base from copper and I attached to the evaporator side so the heat is never a problem. \$\endgroup\$
    – Noahshames
    Mar 19, 2020 at 16:44
  • \$\begingroup\$ @Russell McMahon I used BTA24 before with 3 old tungsten bulbs "Each is 80W" on Microwave sensor it works with no problem. \$\endgroup\$
    – Noahshames
    Mar 19, 2020 at 16:47

1 Answer 1


You must size your Triac for the starting currents.If you do not know the start current and are in a hurry then 6 times the run current is a good guess.

  • \$\begingroup\$ I searched for this it appears I need NTC, thanks. \$\endgroup\$
    – Noahshames
    Mar 19, 2020 at 18:54

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