Electronics > Beginners
How do home power monitors work?
FlyingMoose:
There are numerous home power monitors available on Amazon, etc. They use clamps around the mains wires to measure current but they don’t have any way to measure voltage. I was under the impression that voltage is required to calculate power. Does anyone know how these work? My friend thinks his landlord has rigged the meter to run fast and I want to suggest one of these to check, but don’t know how accurate they are. Do they just ask for the voltage (which may vary throughout the day)? The power is 3-phase delta which I measured at 227v across each pair of phases...
FlyingMoose:
The one I’m considering is the 3 Phase Efergy Elite Power Monitor.
james_s:
I have one that measures voltage using a small transformer that also powers the receiver.
Most of them only monitor current though, they know the voltage because you tell them what the line voltage is when you configure them. The voltage does not vary much in most places so just setting it to 120V, 240V or whatever you get locally is generally considered close enough. These are low cost consumer devices, not precision instruments.
FlyingMoose:
That one I was looking at says it will only work for a balanced load, which the system I’m looking at is not. There are different circuits across all of the phases.
james_s:
Mine is made by Efergy, the transmitter has sockets for two current transformers to handle the split phase panels we have in the USA. There is a spot on the board for a 3rd transformer though so presumably they make a 3 phase version.
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