SparkFun Forums

[renza]

Hi,

Please excuse my lack of understanding.

I have a current transformer here. Say it's rated at 100A and puts out 0.333v when at 100A. Assuming that's RMS, then that's 0.471v peak-to-peak. I need to boost this to get the maximum resolution of my Arduino Due, which has a max input of 3.3v.

I understand that I can use an opamp to achieve what I want. I think I need around 17dB gain.

The resulting AC ouptut from the opamp should be dc biased at 1.666v so that it can be sampled by the ADC.

Not sure what opamp would be best for this, I want a pretty linear output if possible. A quad package would be Ideal as I am measuring 4CTs.

Thanks for any help provided.

[renza]

I have kinda got the result I wanted:



I have used random values for the resistors and caps. Not really sure what they should be either. Also not sure what I opamp I should select, probably want a quad channel one if possible.

[jremington]

No need to use "random values" - there are lots of web pages describing the design principles, but the design you have will certainly work. The voltage gain is 10K/2.2K = 4.5

You should choose a low voltage rail-to-rail op amp for maximum voltage swing.

[renza]

Thanks. Is the Microchip MCP6004 (I need 4 channels) suitable for this application?


http://docs-asia.electrocomponents.com/ ... 381145.pdf

[jremington]

Probably.

[krish2487]

I am not sure you even understand how to size up components for a CT. Read up on current transformer basics first. A CT is not a trivial item. a CT with no burden resistance will KILL you. So be extremely careful.

[jremington]

a CT with no burden resistance will KILL you.

This is a bit of an overstatement, and hardly possible with the sorts of CTs used, and currents encountered in domestic circuits.

A burden resistor is certainly required.