Ray et al.,
Thanks for the info. This may be a red-herring; since I’ve posted this I’ve noticed wifi drop-outs even when no zones are engaged.
That said, if I want to power the pi directly via that micro-usb, do I need to modify the OSPi to disable its 5v supply?
Doing a bit of research I ran across this describing the additional power requirements, especially regarding the built-in wifi. ( http://raspi.tv/2016/how-much-power-does-raspberry-pi3b-use-how-fast-is-it-compared-to-pi2b ). The description said that using the built-in wifi seemed to use 40mA idle and 100mA at peak. I’m not sure how that compares to the USB wifi dongles.
I’m running Ubuntu 15.10 on my pi. I don’t see anything especially relevant in my console log about the dropouts. I’m going to setup munin to log/graph wifi signal. My hope is that should let me figure out if this is genuinely correlated to the sprinkler timing or just periodic crappy signal.