outdoor junction-box and opensource sprinkler controller

[Kdub454]

I recently bought a double, outdoor-rated junction box to house a non-permanent sprinkler controller I bought online.
Ideally, the whole project (5V power supply and all) would be mounted inside the junction box, with a power cord (re-purposed outdoor extension cord) running back to an outdoor outlet.

*So I have three questions:
1.) Is permanently tying the power supply (a gutted apple 5V wall wart) to an extension cord a bad idea, and if so why?
2.) Is it a bad idea to include the power supply in the junction box instead of at the outlet, and if so why?
3.) Is using mains power and low-voltage electronics in one of these reasonable for a semi-permanent outdoor project? (it would be moved inside during off-season)

*In case one (or all) of these is a bad idea
Don't worry, nothing has been implemented yet - I'm still just in the design phase. I wanted to use this as an opportunity to learn about electronics.

Any suggestions or recommendations are appreciated.

[sokoloff]

Your sprinkler controller is likely going to "want" to have 24-ish volts of AC to run the valves anyway. (There are DC valve solenoids, but 24VAC is more common.)

Given that, I'd run a 120VAC to 24VAC transformer someplace dry, then carry the 24VAC across the yard, underground, whatever you need to do, and near the project box turn that into whatever your project needs. That could be another transformer, bridge rectifier, and linear supply, or a switching supply, depending on your interest in selecting or building the various options.

I would not run 5VDC over a long run (due to voltage drop concerns). This is much less a problem when starting with 24V than 5V, of course.

As for having high and low voltage in the same box, it's done all the time and can be done safely, but if you can manage for your box to take only 24VAC, almost every safety concern you have goes out the window, plus it happens to be what you're going to want to switch with relays to send out to each zone box anyway.

[Paul Moir]

A couple further suggestions:
A junction box is far better than an outlet box as the junction box provides no ingress of moisture via the outlet.
Put your wire entries on the bottom of the box only.  Make gravity your friend.
Use cable glands rather than connectors if at all possible.