Basically, I have two 16-relay boards and one 4-relay board in which all 36 relays will all be powering car door lock actuators. The actuator I have that I'm testing with is 12VDC. I am on a limited budget, so I'm trying not to buy any unnecessary parts... Could a kind soul point me in the direction of how to power this mess? I've only worked with USB power up until this point. Any help would be appreciated! Thanks a ton, Cody
What does the datasheet say about your relays?
How do you control all of the relays (what kind of Arduino)?
Just as @ieee488 said, you have to look into the data sheet of the relay(s) to see how much power (current) one relay draws when it is activated. Then your worst case scenario is, when ALL of the relays are activated at the same time which determines the power of your 12V PSU (add the power consumption of the Arduino itself, which normally is something below 30-40mA).
You also have to keep in mind that there are power limitations (output current) of the Arduino board itself.
Common 16-channel relay boards have an onboard 5volt switch-mode supply, so you can't just multiply one coil current x16. The whole board draws about 0.6A on 12volt when all relays are on, including Arduino. Problem with 16-channel relay boards is that you can't separate Arduino supply from relay supply. Not sure what that will do when you connect two boards in parallel. Theoretical pin current for this board is 3.8mA per relay input.
This might be relevant. https://forum.arduino.cc/index.php?topic=365156.0 Leo..