Difference between revisions of "DIY Real time mains power meter"
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=== Rough and ready === | === Rough and ready === | ||
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A quick "rough and ready" estimate of your power use can be obtained with a digital "clamp" meter. This will make a "non contact" reading of the current passing through a wire. So if you clamp it round of the "tails" that connect your electricity meter to your Consumer Unit (CU), you will get a reading of the current flowing at that moment. Multiple that number by your mains voltage (typically 240V), and you will have a an indication of the total power in watts being used. | A quick "rough and ready" estimate of your power use can be obtained with a digital "clamp" meter. This will make a "non contact" reading of the current passing through a wire. So if you clamp it round of the "tails" that connect your electricity meter to your Consumer Unit (CU), you will get a reading of the current flowing at that moment. Multiple that number by your mains voltage (typically 240V), and you will have a an indication of the total power in watts being used. | ||
Now this may be all you need, however there are a couple of sources of inaccuracy in this approach. To assess the actual power being used, you need to know the actual voltage as well as the current, so ideally we need to measure this rather than just assume it is 240V since not only will each property likely vary a little from the "normal" voltage anyway, it will fluctuate throughout the day as the load on the supply changes. The second source of error is that the multiple of volts and amps with AC power technically does not get you Watts, but "VA". The VA reading is the total "apparent power" being used. This may be different from the real power being consumed. This is because the load on your mains may not have a unity [[power factor]]. Depending on what you need to know, this may or may not matter. For knowing what size cables are required for a given load, the VA is a more useful number, since the apparent amps are are real current that needs to be carried. For working out your energy cost you will need the real power consumption in Watts not VA, since domestic electricity meters only charge for the real power consumed. | Now this may be all you need, however there are a couple of sources of inaccuracy in this approach. To assess the actual power being used, you need to know the actual voltage as well as the current, so ideally we need to measure this rather than just assume it is 240V since not only will each property likely vary a little from the "normal" voltage anyway, it will fluctuate throughout the day as the load on the supply changes. The second source of error is that the multiple of volts and amps with AC power technically does not get you Watts, but "VA". The VA reading is the total "apparent power" being used. This may be different from the real power being consumed. This is because the load on your mains may not have a unity [[power factor]]. Depending on what you need to know, this may or may not matter. For knowing what size cables are required for a given load, the VA is a more useful number, since the apparent amps are are real current that needs to be carried. For working out your energy cost you will need the real power consumption in Watts not VA, since domestic electricity meters only charge for the real power consumed. | ||
Revision as of 12:27, 25 November 2022
If you have rather fancied the nifty "in house" real time power use monitors that come with some "smart" meters, but don't fancy the rest of the smart meter, this simple project will get you some of the same functionality.
Rough and ready
A quick "rough and ready" estimate of your power use can be obtained with a digital "clamp" meter. This will make a "non contact" reading of the current passing through a wire. So if you clamp it round of the "tails" that connect your electricity meter to your Consumer Unit (CU), you will get a reading of the current flowing at that moment. Multiple that number by your mains voltage (typically 240V), and you will have a an indication of the total power in watts being used.
Now this may be all you need, however there are a couple of sources of inaccuracy in this approach. To assess the actual power being used, you need to know the actual voltage as well as the current, so ideally we need to measure this rather than just assume it is 240V since not only will each property likely vary a little from the "normal" voltage anyway, it will fluctuate throughout the day as the load on the supply changes. The second source of error is that the multiple of volts and amps with AC power technically does not get you Watts, but "VA". The VA reading is the total "apparent power" being used. This may be different from the real power being consumed. This is because the load on your mains may not have a unity power factor. Depending on what you need to know, this may or may not matter. For knowing what size cables are required for a given load, the VA is a more useful number, since the apparent amps are are real current that needs to be carried. For working out your energy cost you will need the real power consumption in Watts not VA, since domestic electricity meters only charge for the real power consumed.