The first reply above suggests installing a fuse in series to protect the transformer/controller if there is a short in the wiring to one of the solenoids. I have 5 other irrigation controllers, and 4 out of 5 have a 1 Amp fuse in them, so other controller manufacturers have seen a need for them. In the case of the fifth one, the transformer may have become the fuse device. Over the decades, I’ve seen more fuses fail due to old age than due to a problem in the equipment they were protecting, so I view fuses as both a solution and potential problem.
Is there any fuse-type protection on the OpenSprinkler board? If there isn’t, is there any type of solid-state fuse that would do the job, or is a wire-fuse still the most economical device? Some of the 24V transformers that people might have lying around might be more likely to blow something on the board than self destruct without some form of protection.
Where’s a good place to find an inline fuse holder these days, if that is the best solution available?