AC Current Sensing without using a current shunt

tyru said:

JBarnaby,

Did you ever get the circuit figured out? I'd be very interested.

I have a similar interest. Want to use a CT to measure current (0-5 A) on a motor to detect a jam condition using an a/d on a pic micro controller. I need a circuit to convert the AC volt to DC Volt (0- 5 VDC) for the pic input.

found this at the CR micro site.

https://www.crmagnetics.com/pdf/ancrct-4.pdf

Any help would be appreciated

Click to expand...

tyru,
It looks like that is a great solution to the current measuring solution I was looking for...the only thing, the application note above does not give you is any information on the zener diodes....any one have any ideas or suggestions on which zener's to use in that circuit??

Thx

jbarnaby2000 said:

It looks like that is a great solution to the current measuring solution I was looking for...the only thing, the application note above does not give you is any information on the zener diodes....any one have any ideas or suggestions on which zener's to use in that circuit??

Click to expand...

The zeners are to protect the op amp input so 4-6V zeners should be fine.

It should be noted that the circuit in the ap note generates a DC voltage equal to the peak of the AC waveform which is not a particularly accurate way to monitor power. Any noise or distortion (such as from dimmers) will give an inaccurate reading. To get the average (not as good as RMS but better than the peak), move the output resistor from ground and connect in series with the output filter capacitor. Note that this resistor should be at least 10 times larger than the sum of R4 and R5.

Any reason not to use this convenient $3 part?

https://www.electro-tech-online.com/custompdfs/2008/05/0713.pdf

Ubergeek63 said:

Any reason not to use this convenient $3 part?

https://www.electro-tech-online.com/custompdfs/2008/05/0713-1.pdf

Click to expand...

Well, it's for DC current and he wants to measure AC.

The techs at CR Magnetics have been helping me with the values in the circuit. The CR8410 saturates at greater that 2 V. Recommended R1=20 ohm for a voltage of about 100 mV at a primary current of 5A. (Note that the 8410 has a compensated turn ration of 1012). R2=R3=10K. R4=10K R5=500K I was thinking of using a 470K with a 100K mutliturn trim resistor in series for R5 so that I can adjust the gain. Final reistor and capacitor act as a filter. They recommended a 10K with a 4.7 microfarad cap.

see diagram at: https://www.crmagnetics.com/pdf/ancrct-4.pdf

current meter circuit??

Did you get the circuit working? i am looking for a circuit to get dc from a CT so i can interface it with a ADC, i have looked at rms to dc converters and cannot find a circuit for 50hz 0 to 5 A to 0 to 5v for my ADC

Neophysics, you're responding to a thread that hasn't been updated in over a year.

crutschow said:

Well, it's for DC current and he wants to measure AC.

Click to expand...

So use the AC version of the chip