The circuit in the attached pic works 100%
it uses a 3021 triac driver to operate a 230v AC
relay, I tested it and it seems to work fine, but
will it stay reliable or will there be any flyback
voltage that will eventually damage the opto coupler?
do you even get flyback with AC ?
Do I need to add any components across the relay contacts
like a snubber to make them last under heavy loads or to
stop any interference?
The opto seems to work fine in stopping any interference going back
through the circuit causing false triggering etc..
The relay coil draws under 10ma and the triac in the opto is
rated at 100ma at 400V AC. and is non zero crossing.

Everyone is probably wondering why I didn't just use a Solid State Relay..
1. Too expensive
2. Requires heatsinking for heavy loads

Any help or suggestions greatly appreciated,
thanks in advance,
Wayno

 

With a signal of 5V, the current throug the LED is only 3mA. With 8V the current is 12mA. You could increase the current with a couple of mA without any risc of comming close to the absolute maximum rating of the LED's.

Without a snubber the lifespan of the relaycontact will be reduced.

You almost have a SSR. If you replace the relay with a triac you have a SSR. Propably the relay is more expensive. If you use an optocouple with zero switching you will reduce any problem with inrusch current and sparks causing interference.

 

thankyou so much this is the kind of info I needed, with the zero switching did you mean use with the relay or triac? it is in a plastic case that's why I went to a relay vs. the time to make a heatsink etc.