fhteagle Posted August 24 Share Posted August 24 (edited) Greetings all - New Shelly user here. Have it all set up with Home Assistant, but I found something curious looking at the reported data from the unit. The sensor for power flowing through the output / load seems to be way off. Volts and amps reported by the Shelly are both very close to (but usually 1 to 1.5% under) the values I get from my Amprobe ACD-14FX multimeter with clamp ammeter, certainly close enough for my purposes. However, the sensor for reported power in watts is low by a random amount ranging from ~20 to ~75%! For example, my exact readings right now are: Reported voltage: 239.9 VAC Reported amps: 7.425 A Reported power: 398.8 W ( the kWh energy counter reported by the Shelly seems to be incrementing using this value as well) Actual power (assuming a power factor of 1) should be 1673 W, which is much closer to the expected value of this motor. Shelly does not have a way to sense nor correct for power factor, right? The load is _not_ bridged through the N terminals of the Shelly. I have not yet installed an RC snubber, but that should not affect this as the reported amps are very close to multimeter values, right? Seems like a simple math / programming error in the firmware to me. Has anyone else seen this? Have a fix or workaround? Of course I can ignore the Shelly report and have Home Assistant use template sensors to calculate W and kWh, but I would prefer to make the Shelly do its job correctly if I can. Firmware on the device is 20240819-074343/1.4.2-gc2639da at the moment. Thanks Edited August 24 by fhteagle Quote Link to comment Share on other sites More sharing options...
Members thgoebel Posted August 24 Members Share Posted August 24 Power calculation in alternate current systems isn’t simply P = U * I, but P = U * I * power factor. power factor is cos φ. φ is the phase angle between voltage (U) and current (I). Especially inductive load (e.g. a motor) have power factors at approximately 0,7. You should keep this in mind doing such calculations. Quote Link to comment Share on other sites More sharing options...
tvbshelly Posted August 24 Share Posted August 24 (edited) Furthermore: As the load on a motor increases, the PF decreases because the motor draws more reactive power to produce the required torque. Conversely, the PF increases as the load decreases because the motor requires less RP to maintain the same speed and output power. To correctly determine the active and apparent power and the power factor, you can use a Shelly EM or Shelly PRO EM-50 / PRO 3EM. Edited August 24 by tvbshelly 1 Quote Link to comment Share on other sites More sharing options...
fhteagle Posted Sunday at 08:51 PM Author Share Posted Sunday at 08:51 PM Thanks for the replies. I had not expected the PF to precisely 1 but definitely did not expect worse than .9 considering the pump and its load. But, I did figure out the issue that was seriously increasing the load on the motor. Very cool and interesting that the Shelly 1PM Plus can calculate based on PF after all. Quote Link to comment Share on other sites More sharing options...
bonti Posted 10 hours ago Share Posted 10 hours ago Same question. Which shelly devices measure and display active power, reactive power, power factor? Shelly 3EM pro does but shelly pm mini gen3 does not... Which shelly power/energy meters are suitable for accurate measurements of small power consumers, like chargers , standby electronic equipment , between 0-5 W? Quote Link to comment Share on other sites More sharing options...
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