current transformer voltage output

[kareba]

Hello all,

Can someone help me with designing a voltage output from a secondary current transfomer of 60/5 ratio. I need a 0-5v DC output. 5v when the ct sense 60A primary current.

I've tried using a diode (1n4148) bridge but the output voltage get saturated. 60 A return 4.3V but 30 A returns correct 2.5V.

If anyone knew any working schematic please direct me.

 

[IanP]

Measure AC voltage across the 5Ω burden resistor ..
If you face problems with I/U conversion close to the max current you’ll have to decrease the value of the burden resistor ..
Otherwise, try the attached circuit that seems to be much better alternative to the passive bridge rectifier ..

Precision Rectifier Circuit for CT Signal Conditioning
**broken link removed**

Rgds,
IanP

 

[kareba]

Thanks IanP,

What is the recommended zener diode model?

 

[kareba]

I've constructed the circuit in **broken link removed**

im using r1 = 1ohm from 200 watt pot. no zener diode were used.

the output voltage was still get saturated with a value of 60A:3.8V when second opamp adjusted to match 30A:2.5V.

When adjusting 60A:5V the 30A output rise to 3.7V.

When using clamp meter the ratio of input current to output current is linear.Primary 60A produce 5A secondary and 30A produce 2.5A secondary.

From circuit constructed, current to voltage is not linear.

The pic below is my CT, label shows VA:5, ratio: 60/5A, 50/60Hz.

Pls help me get a linear current to voltage relationship. 0-60A with output of 0-5V DC.

Thank you

 

[FvM]

I didn't notice the 5A output range (common with industry standard CT) previously. 1 ohm burden resistor is most likely still too high.
A typically transducer power rating is 1 or 2.5 VA, requiring 40 or 100 mohm maximum burden resistance respectively.
You may want to select an even lower value to increase linearity.

 

[bubulescu]

You can always try a Rogowski coil for the best linearity. Either that or your circuit, it may be better to use an ideal rectifier. There is a very simple and effective solution published by intersil.