Quote Originally Posted by Robin Hewitt View Post
If you want to make your own, Google for the MOC3040

An opto-isolated triac with zero crossover switching.

Add one resistor to limit the gate current and use it to drive the fat triac of your choice.

Not all SSR's feature zero cross over, but that's what data sheets are for :D
I was of the understanding that SSR weren't TRIACS but series hi-power MOSFETS. A TRIAC wont turn on a zero crossing only off, and you usually use a diac to trigger them when the voltage reaches the trigger point, about 25v or so - thats why they work in a dimmer/speed control circuit by delaying the turn on point with an RC network. An SSR is on all the time it is enabled whatever the applied volts although there is a voltage drop across them of about 0.6v and they have an Rds(on) resistance which sounds more like a MOSFET with a series diode (the reverse diode in the second MOSFET).