OpenSprinkler › Forums › Hardware Questions › OpenSprinkler › New and looking for guidance on commercial farm application › Reply To: New and looking for guidance on commercial farm application
While it’s common wisdom that higher voltage is better for transmitting over long distance, it’s important to understand the principle behind it. What happens is that when transmitting electricity over long distance, a considerable amount of power is dissipated as heat on the wires. Assuming wire resistance is fixed, the power waste has a quadratic relationship to the current running through the wire (P = I^2 * R). So to transmit the same amount of power over the wire, it’s better to use higher voltage, because the power being equal, higher voltage means lowers current, hence lower power waste.
However, if you follow the logic above, it’s easy to see that if the current running through the wire is the same, the power waste is the same. OpenSprinkler AC and DC are both designed to supply roughly the same amount of current to the valve, hence the power waste would be about the same. Why does OpenSprinkler AC runs on 24V AC, which is much higher, while the DC version runs only on 9VDC? That’s because solenoids are naturally big inductors, and inductors present significant reactance under AC current. So even though 24VAC is almost 3 times higher, that induces roughly the same amount of current compared to powering the valve using 9VDC. As a result, you don’t need thicker wires when using OpenSprinkler DC.
Long story short, to answer your questions:
-Should I choose AC or DC valves and controller? I’ve read the documentation and FAQ, but I am still a bit unclear. There is power at the controller and at the pump, but not in between.
A: either is OK. Note that OpenSprinkler DC is actually more flexible because it can work with both 24VAC valves as well as 12VDC valves. So it gives more flexibility. Common sprinkler valves are mostly 24VAC.
-Can I run pump start relay to remotely start and stop the pump? How does it communicate with the controller (it’s about 700′ away)? I’ve attached a photo of my pump switch (located at the power pole at the creek). The analog timer is obvious. The other switches are “On-Off-Hand” and “Start”
A: a pump start relay is basically a relay that plugs into the sprinkler controller on one side (think of it as a sprinkler station), and on the other wise it connects to high voltage pumps. So when turning on that station, it turns on the water pump. Your photo didn’t attach correctly (seems too big). If you can resize it to a smaller size it should work. Or you can send it in a email to [email protected].