emonTx three phase guide (UK)


I am about to purchase the emonTX and an emonBase to monitor our three phase power supply but I’ve done a bit of reading on the forum and have come across the need to update the firmware on the TX, buy a USB cable/dev board and generally do some messing around.

I’m up for the challenge but was wondering whether there was a resource to follow?

Also, we have L1-3 +N so I’m guessing I should go for the 4CTs however we don’t really use much power and I doubt we’d ever exceed 25A on each phase so I’m wondering whether the lower, more accurate CTs would be more appropriate? Is that a possibility for the emonTX, or, how inaccurate are the 100A CTs at lower load?

Many thanks,

Welcome, Ben, to the OEM forum.

All the information about the 3-phase PLL sketch is in the pdf file that’s part of the zip file you download.

You don’t of course need a c.t. on the neutral - if that’s what you were thinking - but you can use the 4th channel to monitor a “special” load one of the phases.

All c.t’s are inaccurate at low currents - it’s inherent in the way the magnetics work. But for what it’s worth, I can see a 6 W change in 100 W when I turn my audio amplifier on and off, and that’s with an emonPi on a single phase supply.
You could use the lower rated YHDC c.t’s, but you’d need to modify your emonTx and as it’s basically the same c.t. but with the burden resistor inside, then although you get a higher voltage out and so the ADC in the emonTx has more resolution, the transformer errors are greater. I doubt whether, for the way we use it, there’s any overall gain, because we’re interested in the phase error of the c.t. as well as the ADC errors.

It’s actually very hard to find low current split-core c.t’s, especially ones with a high output voltage that we need.

And yes, you will need to buy the programmer (from the shop at the same time as you buy the emonTx and emonBase), and you’ll need to set up the Arduino IDE to compile the sketch and upload it - after editing it and setting all your options.

Thank you Robert!

I’ve ordered all the stuff and will report back soon :slight_smile: