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I need to monitor electricity consumption

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Good morning all,

Besides the Kill A Watt meter, is there anything else I can use that will simultaneously measure each of the circuits over a period of time so I can determine what circuit is using how much current at what time, etc.

I have different usages at different times of the day but also on different days and using the Kill a Watt meter will take a few months never mind days. :-(

Something that wont break the bank ;-)

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9 minutes ago, Antony said:

Something that wont break the bank ;-)

How big is the bank?

The Eastron SDM-630 Modbus meters are affordable (around R500 or even less, if I recall) and not bad. But I can't find a local source, you're going to have to import from elsewhere.

The next option is a Carlo Gavazzi ET112, they cost around 1k, but those meters have no LCD display and is purely modbus, so you will have to add more hardware to read it (Raspberry Pi and Venus-OS will get you started). Also needs a modbus cable which is around R500, so this is a R2.5k option.

For a basic consumption measure (if you remember it's not perfectly accurate, it's going to be off by 10% or so and does not compensate for power factor), these Efergy and OWL type clamp meters are also not bad. It will get you a basic idea of how much you use and when, just remember... it's not accurate below 40W, and it does not compensate for power factor, so don't expect it to be accurate on individual loads. I add this option because that's basically how I started this experiment. These meters aren't that cheap either, starts around R700 last time I checked.

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9 minutes ago, plonkster said:

For a basic consumption measure (if you remember it's not perfectly accurate, it's going to be off by 10% or so and does not compensate for power factor),

please excuse the question but what do you mean "it does not compensate for power factor"?


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26 minutes ago, Antony said:

please excuse the question but what do you mean "it does not compensate for power factor"?

There is a long post about this elsewhere. But let me see if I can answer this again, perhaps a bit more concisely.

The 230VAC you were told is in the wall sockets is an average value, or a so-called RMS value. If you look at it with an oscilloscope you will see the peaks are at 325V. If you mentally consider the picture of a sine wave, of you shear off the peaks and dump them into the troughs, you will end up with an equivalent straight line of 230VAC.

For a sine wave, the average is at 1/√2 (0.707) of the peak.

You may remember ohms law, that I=V/R. The expectation is therefore that if you put an oscilloscope on the CURRENT measurement, it should follow the voltage waveform precisely. The average current will be 0.707 of the peak. And if you multiply the average voltage with the average current, you will get the real power that is used.

Still with me?

The trouble is that the expectation is wrong for many loads. For many loads their current draw does not follow the voltage. The peak current measurement does not align with the peak voltage measurement, and therefore the whole simplified process of just multiplying the averages together no longer yields you the power value.

The product of the RMS values is called apparent power and is measured in VA. The actual power is called real power and is measured in watts. Apparent power is always larger or equal to the real power.

To calculate real power you must sample both waveforms and integrate over the product.

Back to cheaper energy meters: Cheaper energy meters have a clamp that sits around the cable (it measures the current in the cable), but does no voltage measurement. It assumes the voltage is 230, and it assumes the power factor is 0.9 (which is not too far off a typical residential home).

Proper power meters that install inside the DB does real power measurement. Even the old disk types cleverly has a voltage and current coil aligned in such a way that they do a kind of analog integration in the way they introduce an eddy current in the spinning disk.

So all I am saying is that if you use the cheaper meter with only a current clamp, you won't get an accurate reading. You may be 10% to 20% off. Which doesn't matter when you just want to figure out how much the house uses more or less, but does matter when you look at individual loads.

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14 minutes ago, Antony said:

I want to be able to measure multiple circuits simultaneously but recording each circuit separate, so circuit 1 for lights, circuit 2 for kitchen appliances, circuit 3 for lounge, etc.

Few options available. There's the smappee. This has a couple of current clamps, and it can also disaggregate its measurement to guess what kind of load just started or stopped. It's not cheap, you're looking at 5k or so.

The Open Energy Monitor project has hardware that you can buy, and that has more than one clamp.

What I did back in the day is a combination of the clamp meter and the plug-in meter. I moved the clamp to a new circuit every few days (inside your DB board) to get an idea of how much each circuit in the house uses. Then I used the plug-in efergy meter to individually measure loads on each circuit as necessary.

So basically you use the clamp-type meter to get an overall picture, and the plug-in meter to delve down in each circuit.

The hobbyist in me took over and I eventually built one with ten CTs to monitor each circuit. This allowed me to draw some nice pictures. Again, not the cheapest option as it needs an Arduino and 10 current clamps. I used 10 CTs of the non-clamp variety (I had to remove each wire in the DB and slide the CT over it), and they were R40 a piece already.



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