Total newb, need help creating a prototype CT monitor

Hi there, I'm working on a project to monitor about 60, 20A 120V power circuits in a data center. I'm in the prototyping stage now and I'm a little confused about how to wire this up. I know I need a burden resistor, but I'm out of my element when it comes to electrical theory, etc. Has anyone created one of these? Do you have a diagram you could share?

The two non-invasive current sensor transformers I have are:

SCT 013-030 SCT-013-000

Any help would be greatly appreciated!  I've read the building blocks and I'm still a little confused.

Robert Wall's picture

Re: Total newb, need help creating a prototype CT monitor

The purpose of the burden resistor is to convert the current generated by the current transformer into a voltage. You only need one for your -000 CT, because the -030 has one built-in. That CT generates 1 V rms out for 30 A of primary current, and proportionately less for lower current.
The -000 CT generates 50 mA for 100 A of primary current. For an emonTx, we want to turn that into 1.1 V rms (the maximum that an emonTx can handle), so we use a 22 Ω resistor to do it (50 mA × 22 Ω = 1.1 V).

All the diagrams you need are in Building Blocks. Read it slowly, an article at a time, and allow one to sink in before you move on to the next. The diagram you're probably looking for is in "CT sensors - Interfacing with an Arduino".

But if you're really out of your depth, why not buy an emonTx ready built and tested? — especially if someone else is paying ;-)

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