Hi Rauf,

If you are using it on window Aircon, then for a two tons capacity the the maximum rating is 20 amps. as specified for the circuit breakers.

The starting winding of the compressor takes the peak load while kicking off.

So, you need a triac worth handling 50 amps, with safety of margin large enough.

But,the surge is still a problem. Please visit Tommy Engdhal's page at the following URL and search for triacs in the lighting control/ dimmers section. There you will find many applications on how to protect the triacs.

http://www.hut.fi/Misc/Elec...index.html

If you want a high tech solution, you can go a yard further and develop a soft start and soft stop triac control motor on/off.

On start it gradually increases the RMS value (using zero crossing). The kick off torque is not much compromised as it is propotional to the peak instantaneous voltage. However, the kick off RPM will go low. The big kick off current is avoided. You can do a soft stop the same way.

Steve, you being good at motors, (recall observatory motor postings) please comment, I may be absolutely wrong. This posting was just last thing in a day's work at after midnight, dozing ......


Good Luck

Babar/