According to the basic principle of working of SCR, should get trigger after getting gate signal.I have connected two antiparallel scr's with gate short & not connected to any signal,but scr's are getting triggered & motor is running without any gate signal with input connected to the supply(230ac) & output connected to motor.So can someone help me about this?

 

Sounds like you are exceeding the breakover voltage for the SCR.

 

You cant tie both gates together as they will get their trigger from the other thyristors cathode, you have to use two separate trigger circuits, one for each cycle,


Use a triac they work better

http://www.google.co.uk/imgres?imgu...-uxJUJ-7CMGf0QW-qoC4DQ&ved=0CCcQ9QEwAQ&dur=29

 

Maybe a Triac would work?

 

SCRs will false trigger on high DV/DT signals.

 

SCRs will false trigger on high DV/DT signals.

Perhaps a further clarification - that would relate to the anode-to-cathode dv/dt.