DIY High Power Smart Switch

Those plug-in smart switches that are uniquitous in the market are only good to 10 amps. (most of them) I had one on my dehumidifier project to control when the dehumidifier would turn on and off (by turning it completely off, we save energy and money on the electric bill). After a couple years of use, the “plug in” smart switch died, likely because the dehumidifier draws close to or beyond the current limit of the small relay in those switches. I looked around on the ‘Net and was hard pressed to find something that would handle higher currents. The unit is on a 20A circuit so I needed to be sure that whatever I used was rated to switch that much current. Most of the relays that are out there for “arduino” projects seem to also be limited to 10 amps as well. Boo!

I found a relay on Amazon that was capable of switching up to 30 amps! I’m thinking “this ought to last”, but I need to build a circuit that can energize a 12V DC coil. The ESP8266 module runs on 5 volts, and doesn’t put out nearly enough voltage and current to drive the coil. I needed to add a 12 volt modular switching power source, a 5 volt regulator for the ESP8266, and a MOSFET transistor pack (triggered by the GPIO pin on the ESP8266) to switch the 12 volt supply and send DC to energize the relay coil. Here’s what I used to build this industrial strength appliance smart switch:

• 5″x5″x4″ ABS IP67 rated enclosure to house the smarts
• 1 MOSFET module to switch the 12v relay on and off
• 1 12VDC buck switching DC supply module
• 1 12v coil 30A DPDT relay
• 1 Wemos D1 Mini (ESP8266 Development board)
• 1 adjustable buck regulator module (to feed the ESP8266 with 5V DC)
• 1 330uF 16V capacitor (to filter the 5V input to the ESP8266)
• 2 cable glands (used for AC in/out cable)

Of course, it goes without saying, I installed the open source Tasmota software on the ESP8266 module! I then set pin D1 to drive the relay:

12 VDC buck switching supply:

Here’s a picture of the ESP8266, 5VDC buck regulator, and MOSFET module all wired up on a PCB. This is what gives the switch its smarts and allows the automation system to control it over MQTT/WiFi:

Here you can see the large relay. It is DPDT (double pole, double throw), has a 12V coil, and the switch contacts are rated for 30A @250VAC:

This is the entire smartswitch build finished:

And of course, with power applied (it passed the smoke test!):