As I started to seriously think about replacing my AquaLink I knew that I had to figure out all of the electrical characteristics of the Jandy JVA Valves as well as the Pentair Whisper Pumps and the relays that controlled them.
I determined that the pumps run on 208v and draw a fair amount of current. That being the case I knew that I would not be connecting them to the Pi directly.
I checked out my existing Aqualink and determined that the relays were still in good working order so I decided to use them. They are 24V DC dual pole single throw (DPST). Here it is if you need to buy some.
I still had an issue with controlling even these relays. The coils required 24VDC to activate. The Pi supplying only 3.3v or 5v just doesn’t have the ability to drive them. Even if it could I would need to dampen the fly-back voltage/current when the relay released as that would most certainly blow the Pi up. You know, that magnetic field collapsing through a coil induces a voltage and current. See : Electromagnetic Induction
Granted, I could go and build a circuit to interface between the Pi and the relay, but my electronics skills are a bit rusty for dealing with discrete components. The thought of blowing things up along a trail of trial and error was not appealing to me. So off to Mr. Google for some ideas.
I decided that I would use an intermediate relay that could be driven directly from the Pi. In fact this relay board would perfectly serve the valve actuators as well. You can get these relay boards in a variety of configurations. I opted for the 8 Channel because I would use at least 4 even in the most conservative utilitarian design. I’ll describe my challenges with this board in a future post — but don’t be concerned, they work predictably and are easy to set-up and use.