SONOFF Smart Stackable Power Meter supports up to 128 20A relays

ITEAD has introduced many smart switches over the year under the SONOFF brand, and their latest SONOFF Smart Stackable Power Meter is DIN mountable and made for larger industrial applications with up to 128 devices.

The solution is comprised of the “SPM-Main” WiFi connected main unit controlling up to 32 “SPM-4Relay” units with 4 relays each using RS485 daisy-chaining.

SPM-Main specifications:

  • Storage – MicroSD card slot up to 32GB to store up to 180 days of energy usage data
  • Connectivity
    • Ethernet
    • 2.4 GHz 802.11b/g/n WiFi 4
    • RS485 master
  • Power Input – 100-240V 50/60Hz up to 50mA max
  • Dimensions – 142.5 x 90 x 66.5 mm (PC V0 material)

SPM-4Relay specifications:

  • Connectivity – RS485
  • Power Input – 100-240V 50/60Hz up to 20A per relay, 80A total
  • Power Output – 100-240V 50/60Hz up to 20A per relay, 80A total
  • Safety – Current, voltage, and power overload protection with delay function from 0 to 180 seconds to avoid false positives
  • Dimensions – 250 x 90 x 66.5 mm (PC V0 material)

SPM RS485 daisy-chainingSONOFF Smart Stackable Power Meter works with the usual eWelink app for Android and iOS to allow you to visualize the data which can also be stored in a MicroSD card. There’s also an HTTP API to read the data, which should eventually be documentation on the developer’s website. I suspect the solution may soon end up being supported by ESPHome or Tastoma open-source firmware projects provided it is indeed based on ESP8266 or ESP32 chip.

The SPM-Main communicates with the cloud through Ethernet or WiFi, and with the SPM-4Relays through RS-485 to gather data. The solution will particularly be useful for large installations for example in a shopping mall or apartment building to report the power consumption of each shop or apartment and bill them accordingly.  ITEAD also says it’s also suitable for server rooms and cryptocurrency mining operations.

RS485 WiFi Ethernet power meter

The main unit costs $29.9, while each 4-relay unit goes for $59.9, so for instance, if you were to control 128 relays, the total cost for the hardware would be $748.7, which seems reasonable for 20A relays. If you purchase this weekend, there’s also a 15% discount with HAPPYWEEKEND coupon code. Please note the items are not in stock, so it’s still at the pre-order stage with delivery scheduled to start by mid-October.

Thanks to Hedda for the tip.

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