wildbill:
Yes, kind of.No - The relay defends you against that, but there will be spikes from the relay coil to contend with. It looks like you have diodes on your relay board to deal with that.Relay boards like that (and it looks like yours is no exception) have a jumper that lets you power the relay coils from a shared supply as Blackfin suggests or you can separate them so that the Arduino only has to power the optoisolator LED. My preference is for the latter method, but they are designed to be used either way.
So as far as I understood, leaving with only 1 power supply for powering both the Arduino and the relay module, won't give me the full opto-isolation and I risk frying the Arduino like this? Going with 2 separate power supplies is an overkill for my project. I have looked at the option of using a solid state relay and will this configuration work as proposed in the following diagram? Do I need to use a flyback diode as it was used in the mechanical relay module?
We assume that for switching AC inductive loads its much better to use SSR, since we eliminate the problem of contact welding in mechanical relays due to arcing. Am I on the right track?