Relay problems

[StudentSA]

Good day,

I do not have a circuit diagram at the moment but picture this, 555 timer in monostabe 10s pulse operation -> drives a small 12V relay -> This in turn completes an AC circuit that drives a AC Power Relay which drives an AC Alarm siren.

My system works fine until I connect the AC load (siren). If the siren is disconected, then the 555 triggers and drives the small relay which drives the big relay for 10 sec only then stops until retrigged.

When the siren is connected the 555 triggers the small relay then the big relay then the siren ... BUT... fails to unlatch after the 10s and continues forever.

What could the issue be? - (I have a 1N4007 as a flyback diode in the small relay)

Thanks,
StudentSA

 

[MikeMl]

10uF bypass with short leads, directly across the Vdd to Vss pins????

100nF bypass from 555's FM input pin to ground????

 

[StudentSA]

Thanks Mike, I will try your suggestions.

 

[Boncuk]

Also try a snubber circuit across the AC switching relay.