How to convert output of Current transformer

[howie]

Hi,

I have to convert the output of an AC current transformer (CT: 300A / 5A)into a 0-5VDC range for monitoring an AC current panel meter.

Can someone give me suggestions or schematics regarding this?

Regards,

Howie

 

[srizbf]

connect a 1 ohm resistor in the o/p of current transformer.

take the voltage across it and give it to precision rectifier of an opamp circuit.

you will get what you want

 

[FvM]

Industry standard current transformers often don't have more than 1 VA rated power. In this case the secondary shunt resistor
must not have a resistance above 40 mΩ.

 

[howie]

connect a 1 ohm resistor in the o/p of current transformer.

take the voltage across it and give it to precision rectifier of an opamp circuit.

you will get what you want

Thanks for all your inputs.

I have a detailed discussion attached for your reference.

Regards,

Howie

 

[srizbf]

in your proposed circuit a new ct(mini ct) is to be inserted .

this insertion will affect the existing ammeter readings .(due to ct resistance).

so i dont think the proposed can be good canditate.

instead take the voltage across ammeter and apply it to precision rectifier .
but bursting of ammeter problem will not be solved here.

may require some more revisions based on the constraints.

with regards ,

srizbf
13thmay2010

 

[FvM]

this insertion will affect the existing ammeter readings .(due to ct resistance).

According to the CT operation principle, it would not affect the reading (at least not more than the specified accuracy) if
the total shunt resistance is below the specified limit. As a first point, you have to know the current transformers nominal VA rating.
As said, it may be as low as 1 VA, but also 2.5 or 5 VA are popular types. Than you have to determine the ammeter voltage drop at
nominal load. If it's below the nominal limit (VA-rating/5 A), your circuit can still add up some voltage drop to the total load. Because
the allowed resistance and voltage drop will be possibly rather low, you may want to use AC coupling for the first stage of the connected
circuit and get rid of OP offsets.

Your rectifier circuit isn't suited for AC coupling, because it draws a DC current at the input. You also should use a circuit that is able to
give a correct rectified average value, no a peak value as your circuit does. It will show incorrect readings with varying current waveforms.