# Which circuit is good to measure the current??

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#### Bogdan Mocanu

##### Newbie level 1
Hi,

I want to measure the current from a circuit (~20 A,AC),using Arduino.I made some schematics but I don't know if they will work,and I need the opinion of a PRO.

So,please tell me.Is my circuit ok,will I be able to measure the current with a one of two circuits from the schematics?

Thank you.  1) If the input is a sinewave then 20A RMS produces a peak current of 28.28A. Then the peak voltage across the 10 ohms current sensing resistor is 282.8V which is ridiculous.
2) The opamp will not work because it has no part number and it is not powered.
3) The opamp also will not work because its (+) input does not have a DC reference voltage from a resistor to ground.
4) The opamp will probably oscillate at a high frequency because its output has a capacitor to ground.
5) The opamp also will not work because it has no negative feedback.
6) The opamp will be destroyed by the extremely high voltage from the current sensing resistor.

Why not use a 0.1 ohm sensing resistor? Then the peak voltage from it will be only 2.828V. The diode can be inside the opamp's negative feedback loop so the diode's forward voltage will be almost cancelled.

Hi,

I want to measure the current from a circuit (~20 A,AC),using Arduino.I made some schematics but I don't know if they will work,and I need the opinion of a PRO.

So,please tell me.Is my circuit ok,will I be able to measure the current with a one of two circuits from the schematics?

Thank you.

You can use this circuit and you don't need an amplifier.
The current transformer (sensor) is 20A to 10mA.
The voltage on the resistor is 1V for every 100 ohm.
Diodes are 1N4002

https://obrazki.elektroda.pl/8700229400_1430700628.gif

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