A question that comes up a lot in my Automatic Chicken Coop Door posts is what’s the wiring diagram with a photocell? Ask & ye shall receive!
One thing I’ll say up front while I still have your attention — the wiring diagram above is NOT WRONG. The photocell wiring is not what you’d expect. The black wire is positive, white is ground, & red is the switched output (+).
This is a “dusk till dawn” photocell which means the photocell switches on at night. It’s advertised as waterproof & the light sensitivity is adjustable. It also has fairly mediocre reviews on Amazon so if anyone has a better photocell to recommend, please do!
Here’s the parts list:
- 12V waterproof adjustable photocell
- 12V DPDT relay with base or spend a bit more and get a heavy duty relay
- 12V linear actuator, 8″ extension, IP65 rated w/ built-in limit switches & mounting brackets from eBay (or get it on Amazon)
- 12V programmable digital timer ** OPTIONAL — see timer override below.
The DPDT relay is wired as an H-bridge. This means you make an “X” with power to the normally open (NO) & normally closed (NC) terminals so they have reverse polarity from each other. The “common” terminals connect to the linear actuator.
The photocell controls the coil, the coil switches the relay & that reverses the motor. The linear actuator’s built-in limit switches take care of the rest.
IF IT OPENS AT NIGHT & CLOSES IN DAYLIGHT: Flip the leads to the linear actuator where they plug into the relay.
POWER DRAIN: Although daytime power usage is minimal (0.004 amps) when the photocell is only monitoring the light level, the photocell & relay have a constant power drain at night of 0.12 amps when both the photocell & DPDT relay coils are energized. So I recommend only using this photocell system on dedicated power.
You can still use the photocell system with a solar panel/battery setup, but you would need enough capacity to handle the power drain (12 hours night @ 0.12 amps = ~1.5 amp-hours just for operating the photocell). If you need to conserve power, use this timer-driven system instead.
Here’s a video explaining the wiring:
OPTIONAL TIMER OVERRIDE: Don’t trust the photocell? Add a timer so that closing the door happens regardless of whether the photocell works. Here’s a wiring diagram for that:
Set up one timer event:
- start time = forces the door to close
- end time = door available for photocell to open
So for example, start time of 10pm & end time of 5am.
Keep in mind the timer only overrides closing — if you have a bad photocell that doesn’t recognize daylight, the timer won’t force the door to open.
I use a system of timers instead of this photocell system, because where I live has high winds & I’m concerned the photocell wouldn’t be reliable with blowing dust & snow. The timer system also has far less power drain which is useful if you have a solar-powered coop. I change the open & close times every few months to keep pace with daylight. But the photocell method is pretty slick & if it works for you, great.
Any questions, post in the comments below. Hope this helps!