Electronic – Measuring AC voltage without a transformer using a microcontroller

mainsmicrocontrollerreliabilityvoltage dividervoltage measurement

As I have no practice with AC voltages, I'm asking if the following circuit is reliable for measuring AC voltages about 110Vca and 220Vca 50Hz/60Hz.

I have already made it with a small transformer. But now, I want a more compact way, because I'm planning to do a board for logic control (like PLC) which inputs detects 110/220 as TRUE. A second application is to measure de AC network level.

I have the foolowing questions about the circuit:

a) Is reliable? If not, a fuse could be a solution to stop the things when it goes wrong? (Consider that I plan to split the ~5M resistor in two, 2.4 or 2.7M).

b) In home the pins are phase, neutral and ground. Need I to connect the phase in C4 and the neutral as my circuit ground (or the ground pin is my ground too)? If yes, what to do in case of inverted connection?

c) What type of capacitor must be used?

Circuit to measure AC voltage and simulation

Thanks in advance!

Best Answer

Welcome to EE world.

What happens if a 3kV transient occurs across your components rated for maybe 250V followed by the AC grid and your 10 kA rated breakers before they trip?

Maybe just a "pffft" or maybe it just goes bang and melts a hole in your board and hopefully doesn't start a fire.

See if you can re-arrange this old design with scaled load to get 100:1 or 200:1 part values to attenuate and either make DC signal that with a suitable time delay (100ms?) and triggers a Schottky Inverter to create AC on or off at say 75% threshold using 1.414 * Vrms min.

If this sounds like "word salad" to you, then you do not have the experience to understand.

You could be the next contestant for the global Darwin Awards. A contest to reduce the gene pool of people who make the wrong assumptions about safety..

C4 will not fail here but R11 and everything in between that and, and ,and , possibly including you if you were touching its metal enclosure from a potential arc flash. Myself I have only vaporized a screwdriver tip with sputtered copper across my plastic lens trying to pry off a staple. But it depends where you put your "insulation design" . optocoupler, wallwort supply, plastic case with no human access etc. creepage air gaps on board. etc