I’ve noticed I seem to be able to manually switch on all stations in software. However this can potentially be a problem when your valves together can draw more power than the PSU can supply. While my own setup will use (more expensive) low power valves and my PSU is able to (just) power everything, it seems strange there is no safeguard for this. Maybe by putting in a (user editable) restriction on the number of stations that can be switched on simultaneously?
As for fool proofing, it’s a good idea to have the manual mode switch. So I presume this is the reason it’s in there? However it might be too easily to defeat this safeguard. I’m not really comfortable with a way to blow up hardware in software. 😀
It seems a good idea to add an inline (easy replaceable) fuse to the secondary side of the 24VAC PSU to avoid this kind of mishap. Not all PSU’s have one (mine didn’t as I found out when taking it apart to check).
Earlier versions of OpenSprinkler firmware did have a ‘maximum concurrent station’ limit, but it turns out to be not that useful. So I removed it later.
I don’t think running multiple valves will damage the PSU — first, there is a 2A inline fuse on board which will blow if the current exceeds 2A; also, many common sprinkler transformers are not capable of delivering 2A, so what happens is that when too many valves are open at the same time, the voltage from the transformer will drop significantly and trigger a reset of the circuit, thus releasing all valves.
Thanks for the clarification Ray. I didn’t consider the transformer’s voltage drop. To protect the internal fuse I think I’m going to add a ± 1,6A inline fuse though (I have a small stock for my pinball machines), just to make sure. It’s good OS has an internal fuse, but I want to avoid the need to replace it.