We have a fan coil unit in our server room where I work that utilizes a microcontroller to control temperature and humidity. I have an HVAC and electrical background so I am familiar with instrumentation and controls but I am still on a learning curve with electronics and semiconductors. The project I am working on is building and programing a microcontroller (which operates on 5vdc) to replace the unreliable existing one that is already in place. I have completed the programming and touch screen interface for the controller and am now in the stage of designing a shield (interface board) for the controller so it can operate several 24 vac contactors, relays and a few pump down liquid line solenoids that are on the fan coil unit.
Originally I was going to use triacs with octocouplers but found a solid state relay (AQW212EH) in a DIP package that would allow me to install more outputs on the shield. Here is where my lack of experience comes in. Looking at the data sheet for this relay, pins 1,2,3 & 4 are used for the inputs and 5,6,7 & 8 are used as the outputs. While physically looking at the relay there is a small circle in the corner of the dip package. I assume that this is the anode of pin 1.
So with all of this information and assuming I wired this circuit correctly going off of what I assumed was pin 1 and looking at the Data sheet for the solid state relay I came to the conclusion that connecting 5vdc through a 560 ohm resistor to the input side of relay (anode), the LED reverse voltage of 5V, the Peak forward current of 1A and the LED forward current of 50 mA would be more than sufficient to safely drive the relay. On the output side I connected 24 vac to what I assumed was pin 8 and then pin 7 was connected to the coil of a 24 vac 30 amp contactor. This in theory I assumed would drive the contactor, but alas I let the smoke out of my relay.
Can someone tell me if pin one on the relay is what I assumed it was? If it is, am I using the correct relay for this application (do I need some sort of snubber for this circuit)? If this is not the correct relay to use does anyone have a suggestion on which one I might try?