Electronics > Beginners
Energy Meter power consumption advice/help
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andre123:
I've been assigned to start working on a smart energy meter project, it's been like 10 years since i put any work in AC . I would be sincerely grateful for any constructive advice. Now the 3-phase meters i'm been assigned to work on are class 1 smart meters and apparently they need to comply with IEC62053-21 power consumption limits for voltage circuits which are as follows



Also the since the metrology part/ front end which consists of ,

Current Measurement: Current transformer ( isolated from mains , no neutral reference need to be connected ).
Voltage measurements ( need to be non-isolated and the neutral needs to be connected to the ground of the system ) ofcourse any modem or communication device is to isolated.
The Main SOC (MCU+Metrology) is power hog and it apparently draws around 50 mA alone , the rest of the circuit probably another 20 mA maximum. I've been hinted to study the possibility of using dropper capacitor power supplies+ DC-DC regulators which have high input tolerance (60V) instead of transformer based AC-DC ones. I've been gathering all i can to fully understand the circuit to get 12VDC , seems i'm still going no where.

For now my questions are the following,

Which type of powersupply type (non-isolated) should i use while designing the power supply ( capacitor dropper,...etc) 10VA or 2W , based on my previous calculations 10VA @ 230V will give about 43 mA which is tiny ? I'm confused help ?

How do i calculate the power efficiency of the dropper capacitor , i'm aware of the Pout/Pin but since this has capacitor the equation is not applicable ?

All my findings and work are available here : https://www103.zippyshare.com/v/U7kgRZK8/file.html
Rerouter:
I don't personally like capacitive droppers for long lifetime products.. but in this case because of the following switchmode your not limited to that 43mA, (also plan out your worse case, e.g. the biggest brownout the thing has to work through) e.g. lets say your device uses 50mA at 5V, well if you dropped your mains down to say 12V @ 43mA, then used a switcher to 5V, you end up with about 90mA,
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