Transformer-less solution for a AC voltage meter

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dan2zep

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Hi,

I need to measure and log the power consumption of a AC device. So far I used an Arduino and an ACS712 current sensor and I assumed the voltage was always 230VAC as it's nominally stated.

However I noticed some variations on the voltage values which lead me to believe I need a more accurate measurement. My first try was using this simple circuit:



This works fine on my breadboard but will be very difficult to implement on a pcb because of the transformer size. Can't afford to have even the smallest transformer in my already cramped board.

I will appreciate any help on designing a transformer-less of measuring AC voltage as an analog signal from 0 to 5 VDC.

Thanks!
 

One possibility that you could consider is the use of a linear optocoupler, such as the IL300 for example, but even this component requires a power supply on the non isolated side, but at least in that case the current consumption of the circuitry is constant, and probably a transformerless RCD power source (Resistor/Capacitor/Diode) would be able to feed it without generating too much heat loss.
 

andre_teprom said:
One possibility that you could consider is the use of a linear optocoupler, such as the IL300 for example
Click to expand...

You mean like this circuit?



I believe the left side would be the non-isolated part (AKA the VAC input) and the left would be my analog output.

Both sides have op amps which would be the reason for your suggestion to use a capacitor power source on the right side.

andre_teprom said:
but even this component requires a power supply on the non isolated side
Click to expand...

(Please feel free to correct me if I got something wrong).

What I don't get is how to reduce the amplitude of the ac voltage in order to not damage my op amp?
 

Thank you for your reply!

I reviewed some application circuits for the IL300 and found the one you're talking about.



However I fail to understand how a 230 VAC signal can be reduced enough not to damage the input op amp.
 

Hi,

However I fail to understand how a 230 VAC signal can be reduced enough not to damage the input op amp.
Click to expand...
Usually with a 2 resistor voltage divider...

Klaus
 

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