I've been trying to troubleshoot a Toro DDCWP 4 battery-powered sprinkler controller which started exhibiting strange behavior this summer. This is a basic four-station controller paired with RainBrid DC latching solenoids and valves. It has worked fine for the first three years after installation, so something new has cropped up.
The behavior is this: When one zone/station completes its cycle and turns off, another zone/station will turn on and stay on indefinitely. (Later I discovered that the unwanted station will turn off once it is directed to turn on and off by the controller.) I initially thought it was pressure problems or perhaps improperly adjusted solenoids, but hours of tinkering led to no remedy. I finally started to experiment with wiring changes and measurements with my oscilloscope.
Here is the key observation I made today...
Below is the scope capture of station 2 getting the turn-off pulse from the controller. It's clearly not a textbook-looking pulse. I assume this is due to the inductive load of the solenoid. Disconnecting the solenoid and making the same measurement shows a perfect-looking square wave pulse. Is this more or less an expected waveform? The station 2 solenoid does turn off as directed.
Below is the scope capture of station 1 which shouldn't been doing anything. You can see, however, a 1.8V spike. (Note: The voltage scale is different for these two captures. See the text in the lower-left corner of the screen.) While the voltage magnitude is relatively low, I believe this is causing the solenoid for station 1 to activate inappropriately. It's a DC latching solenoid, so it ends up staying on until sometime in the future when the controller eventually sends it a specific off pulse of its own based on the programmed schedule. When I disconnect the station 1 solenoid it doesn't activate in response to the station 2 activity. This helps to confirm for me that it's not a pressure or leak issue that I'm dealing with.
I don't have a circuit diagram available for this controller, so I don't know what is being done to prevent cross-station interference. It almost looks like a flyback issue due to the inductive properties of the solenoid, but I'm not sure how this could affect a neighbor station. Does this look familiar to anyone? Is there anything I can do to reduce this noise? Or perhaps I just need to chalk this up to a bad controller that needs to be replaced?
