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Hi everyone,

Well, I have exactly the same question as Max. I read through the wiki, forum and shop to search for an answer but I'm still not sure about it.

I would like to monitor 2 x 3-phase AC power and 2 x single-phase power. Is it possible with a single EmonTX and 4 clip-on sensors? I'm ok with an approximation of the current instead of a very precise measure.

Thanks in advance,

Cedric

Hmm, I think you need 2 emonTX, because one emonTX has 4 CT inputs; you want to measure eight (2 x 3 + 2 x 1 = 8. This only holds true if my question, whether the emonTX can measure one 3-phase AND one single phase input at the same time.

I would have thought this to be an an easy questions, given all the wizards around here :)

MaxG

Although it looks as if your shopping list is complete except for a cable to power your GLCD (from the shop or locally), I don't know about the RPi so I can't comment on that. In terms of monitoring power, the emonTx V3 has one voltage input and four current inputs. Of the current inputs, three are high power (100 A) and the fourth is low power (20 A), though by changing one resistor (or adding a parallel wire-ended one - the holes are there) it can be converted to high power.

tocson

You will need 2 x emonTx V3 - the same comment of course about the input capability applies.

Both:

Be aware that using a single emonTx to measure a 3-phase supply depends on the three phase-neutral voltages being in exact balance. If they are not, the resulting measurements will be inaccurate because the sketch has to assume the two voltages that are not measured are the same amplitude as the one measured, and the phase angles too remains correct. Without knowing exact details of the supply system impedances and the loads, it is impossible to say what the inaccuracy might be.

Thanks Robert! Your order review and input is much appreciated. Can I infer that I am better off buying three emonTX (on per phase) to arrive at the best accuracy? I would have to change some sketch somewhere to add the three consumptions into a single value for the display. Also thanks for pointing out the max load for the 4th input, which O would have to change given the maximum of 5kW exceed the 20A specified. I assume can also safely derive that measuring solar consumption on a three phase circuit that the AC-AC adapter is plugged into the same phase the solar feed is connected to.

Interesting times ahead... :)

Hmm, on further thought... why doesn't the emonTX have three AC inputs -- one per phase?

The easy answer first - the emonTx was developed in the UK where a 3-phase supply to private homes is very, very rare (and those that have a 3-phase supply are usually converted industrial buildings). So in most cases it is totally unnecessary.

For a one-emonTx-per-phase solution, see MartinR's "Full-fat 3-phase monitor" You will need the emonTx V2 to use this directly, so as the physical layout of the V3 is substantially different you have an interesting problem in adding the serial communication to the emonTx V3.

As far as accuracy goes - it is totally dependent on how accurately the three phases are matched, principally in terms of voltage. There's an article in Building Blocks that explains how this happens. You need to monitor the voltages at various times of the day to see what is happening, and make a decision based on that. If they stay within a percent or two, it is likely that the overall accuracy will be acceptable. But only you know what accuracy you want. On single phase systems, I've seen claims of agreement with the supply company's meter to better than 1% after careful calibration.

Thanks for the explanation Robert. Makes sense; however, if OEM wants to be truly a world-wide solution, it should cater for these options, I think...

I have been reading through the documentation and building blocks, and understand more by the minute :)

I will have a look at the solution you've suggested -- thanks.

Cost is becoming an issue... an alternative might be this: http://www.ekmmetering.com/ekm-metering-products/electric-meters-kwh-met...