Hi,
I just started a project with 32 relays I bought 2 x 16 relay 12v boards but my question is if I can connect the 12v to a computer psu (yellow wire), I dont know if the 18a of the PSU will fry the board, can you advice me please
Regards
In theory, not a problem. In practice, its clear from the fact that you asked that question that you need to spend some time understanding the basics of how electricity works. The relationship between voltage and current, for example. If you don't do that, then yes, you could fry the board by making a serious wiring error.
Some 16-channel relay boards have a 5volt buck converter fitted that powers the Arduino (not optional).
16-channel boards have optos, but no opto isolation (potentially dangerous for mains power).
8-channel boards do have that option.
Post a link to the one you have bought, and tell us what you are going to switch with it.
Leo..