We’ve been sitting on the driveway gate opener for quite a while. A number of other projects took precedence. But we’ve finally wired it in and tested it last week.

There still need to be some finishing touches on the wiring of the IR sensor which stops the gate closing if someone or something gets in the way. Additionally, we should install a flashing yellow light at the top of the gate to warn everyone around that a car may be going in or out. But at least I can now use a remote to open the gate when we pull in or out, which is really nice at night or in bad weather.

The interesting part is that while the gate opener is designed for 220V AC, internally it drops the 220V AC down to 24VDC to drive a 24V BLDC motor and has 2x 12V lead acid batteries as a backup system in case the AC fails.

We chose this gate opener for this 24VDC drop down feature in order to try to tie it in to the 24V DC solar system we have. Easily enough, the 220V AC feeds into a transformer which feeds out through a bridge rectifier to the main circuit board. There are two terminals on the main circuit board where the rectified 24V plugs into the board, one of which has printed on it 24-30VDC and the other 0V. So we just ran a wire from one of the DC circuit breakers in our DC solar box out to the gate and plugged it into these two terminals, and voila! Solar powered gate opener.

As a final (fun) little calculation…

I wondered how much electricity the gate opener draws. So I opened and closed it a few times and read the current load at the solar controller side. While it peaked at around 5A for a moment when starting up, it settles into just under 3A for almost the entire open/close cycle, with a slowdown step at the end where it drops to less than 1A. I timed the opening and closing time at just under 15 seconds (~14.5sec).

So a single open/close cycle takes 29/3600 = 0.008 hours. Averaging 3A for 0.008 hours gets us 0.024Ah per open/close cycle. Since the batteries connected to the solar system have a nominal 220A capacity, this means we can open and close the gate approximately 9000 times on a single charge. (This assumes no solar charging is done, and we are ignoring the smaller backup batteries in the gate opener unit itself.)

Averaging 5 open/close cycles per day (which is pretty high for our normal use case), this comes out to about 5 years of usage. In other words, the gate opener has a good chance of needing replacement before it will kill the batteries, even if we disconnected the solar panels.

Of course, I don’t mean anyone to take these numbers literally since the battery has a self discharge rate that is faster than this, and lead acid batteries are normally supposed to be replaced about every 2-3 years. But you get the idea…

The only real point of this calculation is to confirm that the gate opener isn’t much of a drain on the solar powered DC electricity system. And that appears to be the case.