The evapotron has evolved a complicated power, sensing, and control circuit. I’ll go into detail later, but for now, here are the constraints:

  • it has to contain 2 heavy lead-acid batteries, a charger, a power bus, 2 relays, and a panel with circuits + Arduino, and have an LCD readout through the top;
  • it has to take in 8x16ga cables on one side, and 2x16ga AC power lines on the other;
  • it should be weatherproof, seriously.

I got a big polycarbonate enclosure from Digikey. Great box, reasonable price, but DigiKey ripped me off on shipping, that was seriously uncool. I spent a lot of time thinking about how few cuts I could make through the box. Two cable outlets, ok, necessary, manageable with cable glands and silicone putty. But how to secure the big, unwieldy batteries to the enclosure?

I think that by making very small slits, I can zip-tie the batteries to the wall. This was the only solution that worked. I looked hard for ways to use adhesives of various kinds to secure the batteries and other pieces to the inside of the enclosure. The batteries are too heavy to be held by any adhesive, so I cut slits in the enclosure wall with a Dremel and ran a zip tie through.

I’ll clean it up with sandpaper and seal the slits with silicone before it goes live.

Here are the adhesive experiments.

The idea is that I’d adhere some kind of machine screw set in a rubber foot to the surface of the enclosure. Then I can mount a plastic plate on the screw. The busses, relays, circuits, and Arduino will all be mounted on removable panels so I can work on them outside the box.

For adhesives, I tried “Weld It,” cyanoacrylate (e.g., Krazy Glue), and plastic bond epoxy. “Weld It” failed instantly. Cyanoacrylate did a funny thing: it failed to bond rubber or plastic to the polycarbonate, but it made a very impressive bond between the head of the machine screw and polycarbonate. The epoxy (in addition to being a horrible mess to work with) made a weak bond between the rubber and the polycarbonate. Ok: solved, cyanoacrylate it is.

Here’s the current enclosure layout:

You can see the batteries held by the zip tie and by brackets that are glued to the enclosure wall. They’re removable by cutting the zip tie. Next to the battery is the charger, from which the AC connection will exit through the cable gland on that side. The plate on the floor of the enclosure holds the 12v/GND bus (white plastic+brass), the incredibly useful 5v switching regulator from Pololu, and the 5v/GND bus (wire snaps from Adafruit). The plate on the back wall will hold the circuits and Arduino. Missing is the LCD screen which will be glued to the top of the enclosure. Time to build it, but there’s never enough time.