In March 2015 I posted a method for making an automatic chicken coop door using two timers & a DPDT relay, but the timer setup was complicated — one timer provided power, while the 2nd timer controlled reversing polarity & had to turn on simultaneously with the power timer. Not easy.
Here’s another method of wiring the timers that’s more straightforward. One timer opens the door & the 2nd timer closes the door. One event per timer … Simple, easy, inexpensive, & should be as reliable as the old way.
This new system uses a $9 dual-SPDT relay module which replaces the DPDT relay in the old design.
Any 2-channel SPDT relay module should work. Typically they have 6 terminals on one side: NO/NC/COM for each relay, & 4 terminals on the other side: signal inputs for each relay (IN1/IN2), & power for the module (marked as +/-, or VCC/GND).
The timer wiring is the same as before — daisy chain power to each timer, & then to the module. Jump (+) to both NO terminals, and (-) to both NC terminals. Connect the actuator leads to the COM terminals. Run the output from each timer to the module’s IN1/IN2 terminals.
- Dual-SPDT relay module ($9)
- (2) 12V programmable digital timers ($5 each)
- 12V linear actuator, 8″ extension, IP65 rated w/ built-in limit switches & mounting brackets (~$55)
I’ve received several questions about my wiring diagram’s purposefully ambiguous “power supply”, so here are some different options.
Solar panel: You can use a very low-watt solar panel connected directly to the battery with a fuse, so that the solar panel acts as a trickle-charger. The problem is the solar panel also slowly discharges the battery at night, & so this system relies on whether the solar panel can generate more power during the day then it uses at night – normally not a problem, except if you live somewhere like I do without much sunshine in the winter.
Solar panel w/ controller: This uses a solar charge controller which regulates power to the battery & automatically disconnects the solar panel at night. You can use any size solar panel, although panels over 20W are probably not necessary unless you are using a different system with a higher constant power draw (like a photocell) rather than the two timers.
- 10W 12V solar panel ($30)
- 12V 7-amp battery ($17)
- 20-amp 12V solar charge controller ($20)
- inline fuse holder ($5)
Dedicated power: If you have A/C power to your coop, you can use a 12V power adapter with an amp rating higher than the power draw of the linear actuator. This method is by far the least expensive, but if the power goes out, your chicken coop door won’t open/close.
Dedicated power with battery backup: Nice method that handles power outtages. With this system you need a trickle charger (sometimes called a “battery maintainer”), and a 12V battery with an amp rating higher than the power draw of the linear actuator. As with any battery, you should definitely put a fuse on the positive lead coming off the battery.
Fuse sizing: Typically the fuse is rated 50% more than the maximum power draw of the linear actuator, so for instance if your linear actuator is rated for 5 amps max, use a 7.5-amp fuse. For a 6-amp linear actuator, use a 10-amp fuse.
Wire gauge: 16-gauge or 18-gauge wire should be fine, unless you are using more than a few feet of wire for some reason.
Wire connectors: I used spade terminals to connect wires to the timers & battery tabs. Keep in mind you’ll need to use a larger size terminal (than your wiring) when you splice 2 wires into one terminal. You can order a nice assortment of terminals on Amazon for $14, or your local hardware store typically sells individual spade terminals from the small parts drawers.
Troubleshooting: If the actuator runs backwards, switch the actuator leads where they plug into the COM terminals. If the wrong timer controls the wrong event, switch the timer output leads either where they plug into the IN1/IN2 terminals or at the timers (doesn’t matter, same result).
Circuit Details: With neither timer activated, both motor leads are (-). With one timer/relay pair switched on, one lead switches to (+), the other stays (-) & the motor either runs forward or reverse. With both timers activated, both motor leads are (+) … that shouldn’t happen with your timers set properly, but it’s fine if it does (not a short circuit).
Don’t shoot the hobbyist: I’ve only been running this new setup for a week so I can’t vouch for it’s longevity yet, but I don’t have any reason to doubt it will be as reliable as the prior design. So far I’ve only had to replace 1 timer that stopped switching after 5 years of use.
Questions for electrical engineers:
- Does this module handle EMP from the actuator motor being switched off, or ideally should I add something to manage that? There are a bunch of other components on the circuit board in addition to the two relays, not sure what it’s designed to handle.
- I’ve come across this relay module used with IN1/IN2, NO1/NC2, & NC1/NO2 each jumped together, like this, which seems to provide the same exact function as a single DPDT relay wired as an H-bridge. To me this makes very little sense — essentially using two SPDT relays to accomplish the same function as one DPDT relay, but with more complicated wiring & greater possibility of component failure. Are there any benefits to this setup over a single DPDT relay?
- Is there any benefit to using a motor reversing solenoid over this 10-amp relay module (perhaps built-in handling of EMP)? Or are those solenoids just primarily designed to handle more amps & a longer duty cycle?
Happy chicken coop dooring. Any questions or comments, let me know!