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.
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!