Relays for Home Automation

Switching things off and on again is one of the main features of home automation. It is usually achieved through electronic switches or relays that are controlled by NPN or PNP transistor outputs which in turn are toggled by even lower power and isolated microcontroller output pins.

Songle, Omron and Panasonic Relays
Songle, Omron and Panasonic Relays on a DIN rail.

Turns out that relays themselves have very different power requirements — from 0.1W to 1W or 0.8kWh to 8kWh of energy to stay “on” for a full year. I recently order samples of the following relays for switching the room lights:

And here is their power consumption which I’ve verified in my own testing:

  • 0.12W for Panasonic PA1A
  • 0.36W for Songle SRD-12VDC-SL-C
  • 0.53W for Omron G2R-1-E

So choosing a relay that matches the switching power requirements can reduce the switching energy consumption by up to 80% or more.

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