The current firmware allows multiple valves to open at the same time. Is there any limitation in the OpenSprinkler hardware board that would max out the number of simultaneous valves? Does each valve have its own triac or other power control circuit for instance? I realize you would have to size the transformer big enough for the in-rush currents.
Which raises another question, since in rush current is 2-3 times as high as steady state current for the valves, it would make sense if the OS firmware were to stagger opening the valves by one second. So if five valves were opened “simultaneously”, it would do so over 5 seconds. Or could you use the per station Station Delay? If you gave each non-sequential station a different station delay (like 1, 2, and 3 seconds for three stations), then would the non-sequential stations each open 1 second apart?
You are right that each zone has its own triac, which is rated 800mA, and that’s necessary because each zone needs to be switched independently.The power adapter does have to be beefy enough to support the number of concurrent running zones. Most people probably won’t need more than 2 to 3 simultaneously running zones, so the inrush current isn’t that much of a problem. If you do want to run many zones simultaneously, what you mentioned about staggering them makes sense. In fact, this is already implemented for remote zones — any virtual zone (including HTTP stations, RF remote station etc.) that’s scheduled to open at the same time with other zones will all be staggered with 1 second delay between each other, for the simple reason that you can’t simultaneously send out multiple HTTP or RF commands at the same time. So that staggering implementation can be easily modified to support the physical zones.