Why this Simple Watt Meter for 220 Volt Circuit works?

Thread Starter


Joined May 12, 2020

I'm just a begginer student. I found this circuit of a wattmeter that works only with resistors. Can someone explain to me how the 33k resistor give a voltage of 1 mV to 1 Watt? I did not understand why these resistor values has been chosen and why the it measures only in the 33k resistor.

Link: https://everycircuit.com/circuit/5290189996163072/simple-watt-meter-for-220-volt-circuit

I made a version (only changing one resistor value) at Fasltad: http://tinyurl.com/y7uqu8n4 (the url was too big).

Can someone help me? Thank you!


Audioguru again

Joined Oct 21, 2019
Two parallel resistors are 470m ohms each. That is 0.47 ohms each. They make what is called a "shunt" in a current meter. They pass most of the current and the 33k and 7.5k voltage sensing resistors pass only a small current.