We put an electric gate opener on the gate on our driveway. There’s been a lot of tweaking and configuring, but it basically works. The solar panels, though, are insufficient to recharge the batteries after a day of contractors coming and going — this is one of the drawbacks of living in the redwood forest; there’s lots of shade at the perimeter of our property. The gate opener control box is located in a pretty inconvenient location (up a steep slope) and anyway, the batteries are in a box that is kept closed with screws, which means that changing the batteries involves a walk through the forest, up a hill, with a screwdriver and a pair of batteries, as well as running the very real risk of dropping one of the said screws into the forest mulch and needing to grovel around for it. Also, depending on how much indirect sunlight the solar panels got, the batteries may need to be changed today. Or not.
Of course, we could run about 300 feet of low voltage wire from the PG&E box at the bottom of the driveway up to the gate controller. This would mean the batteries only get used to open and shut the gate when PG&E fails to deliver electricity. It would also cost…a lot. Either we’d be stringing wire on poles, or we’d be digging trenches and burying conduit. The electrical contractor looked at the situation and said that yeah, we could do that, but it would probably be cheaper to get new electrical service provisioned by PG&E, and have the new meter & box put on a utility pole that’s just a couple of yards away from the gate. Which would be fine, I guess, except for the price tag, the permitting process, and the time it’d take. And, of course, PG&E.
What I’d really like is for changing the batteries to be a low-cost operation. Ideally, I’d have a box with batteries inside and a socket on the surface somewhere and I’d be able to carry that box up to the gate and just unplug the existing box, plug in the new box, and take the discharged box back to the house and plug it into a trickle charger. Also, I’d like to have some kind of monitor on the batteries so that when they get low, I know to go swap the boxes, before the contractors show up and can’t get in.
Mighty Mule, the manufacturer of the gate opener, does not really believe in quick-connect stuff. The thing I want doesn’t exist, as such. So I’m building it.
System Components
Battery Box
There exist boxes which are intended to keep batteries shielded from the weather, for storage. You can get them at most auto parts stores. However, these boxes are sized for car batteries, while the batteries used by the gate opener are the size of motorcycle batteries. (They’re not actually motorcycle batteries, but close enough.) From an electrical perspective, a car battery would work, but it’s way bigger and heaver. So, I didn’t want to just buy a pair of $25 battery boxes that would wind up mostly being full of empty space (which, let’s be real, means spiders, ants, and millipedes).
I found a box that’s suitable for outdoors and which will hold the batteries: Altelix 10x8x6 Fiberglass Weatherproof NEMA 4X Enclosure with Quick Release Latches. I’ve already got four batteries, two for the gate and two to swap in. The box is big enough to hold two batteries. So, two boxes ordered.
Inside the box, I’m putting two ES7-12 batteries, wired in parallel. So, I need two red cables to go from the battery positive terminals to a Wago connector, two black cables to go from the battery negative terminals to a second Wago connector, and an SAE socket with cables to go to the two WAGO connectors. I’ll drill a hole in the side of the box and mount the SAE socket there, sealing the hole with silicone caulk. Once wired up and closed up, the box is now a big 12V battery with a convenient socket on it.
Battery Monitor
I’ve already set up an outdoor WiFi network for the far-away IoT devices, and I’ve got a Home Assistant set up to help me keep an eye on everything (because everything is far away and needs batteries). So, I went looking for a monitor and, sure enough, someone has already built this part and is offering it for sale! The GS BM1 Battery Monitor connects to the wireless network and integrates with Home Assistant. I wired it in to the gate control box, putting its leads on the incoming power cable, meaning I can set up notifications when the gate opener batteries are getting low. (As an aside, as I think about it, I think I want a couple more of these things. We have two cars that we use all the time, a golf cart that we use once or twice a week, and a pickup truck we use once every few months. I think it’d be a good idea to stick a monitor on the golf cart and on the truck and then get alerts when they get low.)
Power Cable
The last part is a long cable to connect the battery box to the gate control box. One end plugs into the connector on the battery box, and the other end plugs into a pigtail wired to the control board.