I know I’m late to the party on this, but I had the same issue with an RPI3 and the 16 relay sainsmart board. I read that others were having the same issue apart from OpenSprinkler and solved it by connecting the 3.3v gpio pins instead of the 5v pins on the RPI3. I tried it out and it worked. And in my case, the PI3 is being powered from the 3.3v pins, so only the 24vac and 12v dc psu needed.