The Solar Garage Door Opener

Well, not really. More like the 12V DC powered opener. I’m sure they exist, and they probably cost an arm and a leg. But let’s see what we can do with a more conventional model; both for cost and for parts. The idea is to use a 12V deep cycle battery charged by a 100w panel with charge controller to run a garage door at a remote building. The primary use for the power is for lights inside and out, but if a suitable door opener can be added, why not?

After some googling, I found several commonly available openers (Sears/Craftsman, Champion to name a couple) that possessed a battery backup feature. Checked the batt specs and they were indeed 12v. Their description seemed to match what I was looking for (door operation with the loss of 120VAC up to a dozen or so times). But such ‘fancy’ openers also have lots of unneeded features. Would they work at all on DC? Would they be totally useless for the life of the opener? Let’s find out.

After shopping around I picked up a new, surplus ¾ HPS Belt Drive Craftsman model off that popular internet auction site. Model 9-54918 (139.3043). It came with a pair of remotes, a wireless outdoor keypad, the required electric eyes and a switch panel that included control of the lights and door plus backlit LCD display with program buttons. Hmm.

Right off the batt…let’s tear this thing apart and see what we’re working with. Well, the switch panel with all the fancy features, like motion detection and display of interior temperature, connects with only two wires, so there’s a communication protocol taking place, and it’s safe to assume microprocessors at each end. Indeed, the rear of the opener contains a circuit board with micro, relays, driver transistors, etc. And you know what else that means? Software.

Standy Curent Measurement

The drive motor itself is the type used in automotive window regulators and to cycle windshield wipers and is pretty easy to drive. +12v on the red lead and -12V on the other will drive it one direction; reverse polarity to go the other way. So, if you want a brute force drive method and have no need for wireless control, cut those leads, run them out and there you go. However, you now have no safety features nor remote operation. There’s probably a better way…and there appears to be.

First, the thing is too smart for its own good. Buttons and indicators on the rear allow for setting the upper and lower limits of the door and for entering a learning mode to communicate with remotes. When first connected to AC, a rapid flashing green led indicates battery charging. This will turn orange when fully charged. The unit also communicates by flashing the 120VAC bulbs to tell you what else is going on, such as a wiring or communication error with the photoeyes, or restoration of AC power. I would like to rewire one of the two lights for 12VDC operation, and seeing as a basic SPDT relay on the PCB turns these on and off, some hacking should be easy, but it’s not. Software detects the absence of AC power and prevents engagement of this relay except when the motor is energized, so no time delay. And while the wall control has a Light pushbutton and the remotes can be programmed to use their other buttons for remote lighting, that’s a no-go on DC only. At least the 120VAC convenience sockets are wired with spade terminals, so a little rewiring allows the second bulb to be pulled out of circuit and wired to DC as we see fit. A 555 timer triggered off the relay coil (that only energizes during motor movement) should do the trick.

D24 is in the center of the relay footprint. Sharpie + and - marks denote
coil pins that will trigger external time-delay circuit.

The photo eyes must be wired and installed, and I believe they also have serial communication to the opener. The good news is a visible LED is mounted on each to see when they’re connected and when they’re drawing power. There’s no tell-tale click of a relay when the eyes are blocked, so bypassing to conserve power is not an option. However, there’s some good news. After 5 successful door open/close cycles (aka learning mode) once power is connected, the eyes power down when the door is closed. This cuts standby current in half (0.130A drops to 0.055A in standby). That’s less than 1 watt in the quiescent state.

If you think you’ll just bypass the transformer and inject your DC there, that could work, but be aware the system voltage is in the low-20’s VDC so it’ll take more than a 12V battery to make it work. I have to assume the way the software is written that you’ll also draw more standby power going this route, as it will think it’s connected to AC.

When on DC-only several other things happen. The backlight is shut off on the wall control and the LCD lets you know you’re off the grid. The light button is disabled as well as temperature and motion sensing. Luckily the door button still works. The wireless remotes still work, too.  A “Time to Close” feature that automatically closes the door x-minutes after opening is disabled. Big deal.

While I haven’t buttoned the unit up and installed it yet, one glaring issue is that if DC power is removed while not plugged into an AC outlet (such as swapping your battery) the unit will not power-up again without momentarily seeing AC. And you can’t just leave the onboard battery in parallel with the external deep cycle source as it’s small enough to be damaged/overheat and lead to bad things. Since this should be a rare occurrence, it might be possible to wake it up with a little AC inverter plugged into my cigarette lighter should the need arise. Current would be minimal, we’re just jump-starting the micro. 

Update: The unit has been installed and works! I used 14 awg NM romex for the 12V power and I suppose voltage drop could be improved with 12 awg or larger, but honestly these openers were never designed to be "speedy" on DC; their aim was to get the job done. At less than 20' from the battery, this doesn't appear to be an issue. 

I used a 12v inverter and a pair of aligator leads to jumpstart the unit. After leaving it powered for 30 seconds, I simply disconnected the clips, put my wire nuts on the DC leads and coiled up the AC cord. Disconnect too early and it won't go into DC mode. If one really wanted a belt-and-suspender approach, one of those cheapie 150w self contained inverters could be mounted inside the opener case (plenty of room) and a toggle switch added to the exterior. The AC cord could be removed and rewired internally to the inverter. No futzing necessary. 

Also of note, this unit learns remote controls dynamically. You press the Learn button on the unit, then hold in the wireless remote button until the unit flashes its lights. Well guess what...on DC it won't flash its lights (obviously). It won't even click its relay....but it will still pair with your remote. Simply hold down your remote button for 30 sec and then see if it works. If it didn't learn it, try again but hold it down longer. Eventually it'll get through all the codes and have picked the transmitter up. And there you have it-  A custom 12V opener with remotes and minimal power consumption for the price of a discount standard model. 

(Update 12/23: It's one month later and the unit works perfectly. No resets, no outages, no issues.)