Relay in race condition...continuously on-off.....

[amitjagtap]

Long back (5-6 yrs back) I designed a simple 555 monostable multi to drive an AC motor using a relay....I tested a circuit...relay switching was fine(without motor connection)...but when i tried with AC motor....the relay was continuously in ON - OFF state once trigger has given...I tried some solution too...but cant find out the proper soluation and reason.. and I left it as it is...

Can anybody explain me the reason and very proper solution to this...:|

 

[ted]

It would be a lot easier to answer your questions and help you if you would provide some documentation. A schematics diagram could be a good start. Also, how you constructed it (on a circuit board, "wiring in air", or whatever). Maybe you could even add a photo or two?

In general terms, I can say, however, that the problem might be related to transients generated by the AC motor. In such situation good by-passing power supply, having correct grounding, maybe some shielding of wires/circuitry, and avoiding of "magnetic pick-up loops" in sensitive places of the wiring are usually necessary for reliable operation: You got a significant source of noise and spikes in the sparking relay contacts switching an inductive load (the motor)!

 

[Senthilkumar_rjpm]

Which driver circuit you are using to drive relay? Which motor u r using ie.HP? Due to induction load (motor) it may not working properly. The simple solution is connect 440v metal oxide variastor(MOV) across motor supply & ralay contacts... it may solve ur problem...

 

[amitjagtap]

Well,
As I said I did it long back. Now i cant provide any document or photo. I can tell you how the circuit was.
It was simple 555 monostable generating a pulse for 2-3 sec. for which the AC motor should be ON.
Output of the 555 was connected to relay driver transistor (I think it was 2N2222), which supposed to drive the relay for specified time. I implemented this on a general purpose PCB.

 

[prmurthy]

Hi

Here is some interesting link for basic electronics simulation. You can build any basic electronics with 555 or 741 etc and see the results.

Circuit Simulator Applet

Thankyou