Accuracy of Wireless Power Metering

Wireless "power" meters like the Efergy don't actually measure power. To keep their connection simple and cost down, they only measure peak current and they make three assumptions that are not always warranted and that lead them to overestimate the power.

  1. They assume the RMS voltage is 240 V (or whatever voltage you tell them).
  2. They assume the current waveform is sinusoidal and so RMS current is peak current divided by the square root of 2.
  3. They assume the current waveform is in phase with the voltage waveform and so power is RMS current times RMS voltage.

Assumption 1 is usually not a great source of error, but 2 and 3 can be, and are both often described as the meter ignoring "power factor".

Assumption 2 can overestimate power by a huge amount in the case of some low powered electronic devices and is likely what's happening here. The appliance only draws current in a very short "spike" at the peaks of the voltage waveform, and the "power" meter assumes the peak value of this is the peak of a sine wave of current.

Assumption 3 can overestimate power by up to 40% in the case of loads which are motors, such as pumps. A common "phantom" is a solar hot water system circulating pump for split systems (i.e. where the tank is not on the roof). A power factor correcting capacitor can be installed across these. This won't save any power, but will at least make the wireless "power" meter read more nearly correct.

The only way to know is to use a proper power meter that simultaneously measures voltage and current and multiplies their instantaneous values together, making none of the above assumptions. But these are more difficult to wire in, in the case of a permanently wired appliance, and this should only be done by an electrician.

Efergy wireless energy meter with LCD display

We install solar systems in Northern NSW and Southern QLD.

Gold Coast (from Coolangatta to Southport), Nerang and Hinterland (Beaudesert) and out West (Warwick, Stanthorpe, Killarney)

Northern NSW (Tweed Heads to Yamba, including Evans Head, Byron Bay and Ballina); the Far North Coast Hinterland (Grafton via Lismore to Murwillumbah) and out West (Casino to Tenterfield, including Drake and Tabulam, as well as Woodenbong and Bonalbo)

For larger system we also go up to Brisbane or down to Coffs Harbour and even Glen Innes. Other places by arrangement.

We are Open for Business

Rainbow Power Company would like to assure our customers that we are trading (not quite as normal). System designers are working from home and can customise a quote for you (free of charge) over the phone and online. We are still dispatching and posting items, with safety precautions in place. You can still order online or over the phone, and pick up items from RPC (our show room is closed however, and appointments must be made to pick up orders). We are still doing site inspections, keeping the recommended social distancing.

Contact us

This is the perfect time to start thinking about your power needs for the future, reducing your bills, and safeguarding against future power outages, so call today and get in before the oncoming solar rush. PH: 02 6689 1430 or send an enquiry
..stay safe and healthy, your RPC family