3Phase + Solar Configuration Assistance

Hi All,

I’m in the process of designing a monitoring system for a 3-Phase system which includes a single phase for solar.

I’m leaning towards Option1, is it possible to approximate the 3P load using the emonPi or must it be done with the emonTX?
Also, I’m assuming the 3 phase for the aircon would be relatively balanced, does anyone have any experience to confirm?
Besides the loss of monitoring individual circuits, is there anything else I should be wary of going for option 1 over 2?

If you have any recommendations for improving this system, please let me know.

Option 1


Option 2

I also have an off-peak HWS system, it has two elements where one is ripple controlled and the other is not.
Is it possible to measure the peak usage by running both wires through the CT as in the diagram below? I would prefer to do this than to clamp on the utility side of the meter.


As long as the wires fit comfortably and do not strain the CT that will work fine.

In your second option you seem to have the hot water heater CT (which is on red phase A) connected to to emonTx-2 which is predominantly grey phase B, is that intentional? Are you thinking of running the 3-phase FW on that emonTx?

What is the reason for asking about running the approximation sketch on the emonPi? in your option 1 diagram, both CT’s are on the red phase A. Is it because you cannot get a red phase A socket near the emonPi location? The second option looks like it would need the same voltage signal in the same/similar location.

Since you have a bias of 2 mandatory circuits on the red phase A, for option 2 to work at it’s optimum, I think you would need an emonpi and 3 Tx’s so that you could have the emonPi and one Tx on the same red phase A, this would even things up and also give you a spare blue phase C CT for the Garage or oven, so all of your circuits could be quantified, either by direct monitoring or by calculation.

The obvious benefit of the second is accuracy and number of channels, however I can see the cost does make the first option seem more appealing. The single phase PV may skew the data a little when using option 1 as might the heavy load of the HWS. But as long as you are ok with a pretty good approximation you should be fine.

I can’t answer the question about AC off-hand, I haven’t had too much experience with 3phase AC units, I assume the compressor is 3phase other wise there would be little point in being 3ph, so I would guess it’s fairly balanced, only the control electronic are likely to be on a single phase and possibly a negligible amount. (I’m pretty confident someone will correct me if I’m wrong there)

No, this is an error. My guess is that the HWS is on phase A, but since it connected internally on the utility meter, I can’t confirm.

I would like accurate measurement of all 3 Phases coming into the premises, but only approximation of the A/C load. The question was really just one of configuration. i.e. do I need to swap the emonTX and emonPi around.

Maybe I misunderstand, if I want accurate measurement of 3 Phases, do I need 3x emonTX’s each with an AC-AC measurement, or can it be done with 1xemonTX with only 1 AC-AC measurement?

I guess with option 1 I was hoping that bymeasuring all 3 phases from the meter, but then only approximating the A/C load, then this should a reasonably good outcome.

I think you are probably right, the compressor will be on 3 phase, but all electronics and probably the indoor air handling unit will be on a single phase.

Do you have a multimeter capable of reading 415v AC and are you competent working with high voltages?

Measuring from the HWS supply line, If you measure AC voltage between there and each of the phases at another location where the phases can be identified (eg dist board?) you should measure ~415v to the 2 “other phases”, you will get (close to) 0 volts when measuring between 2 points on the same phase. So of the 3 measurements, the one that is 0’ish not 415v is the phase your HWS is on.

But please do not attempt any work on high voltage circuits unless you are confident in what you are doing.

Each CT needs a voltage signal from the same phase to get an accurate power reading. This becomes more important with non-unity loads (eg the AC). To measure 3ph the ideal is to have 3 Vac signals for the CT’s to use, but that is not always possible and sometimes it’s cost prohibitive, so there are other ways of doing it, eg using a 3ph sketch that uses the ac signal of one phase to guess the other 2, this is reasonably accurate on well balanced 3 phase installs but not so much when there are differences in voltage signals between the phases.

Your first option shows multiple phases connected to one device, so I assumed you had chosen to use a 3ph sketch, accepting it’s shortfalls.

the second diagram uses a device per phase (except for the HWS), so knowingly or otherwise, you have suggested a more accurate method as each ct has a voltage signal to work with, assuming you were planning on an AC adapter for each device.

So the increased accuracy in the second diagram comes prodominantly from being 3 “per phase” devices and not so much because of the single CT in the first diag.

In the first diag, even the meter CT’s could be somewhat off (although not definite), because of the way the emonTx will guestimate 2 of the 3 phases, then to that you will (I assume) triple the AC power used, this will work as an indication and you might get pretty reasonable results, but it’s not guaranteed.

Either way, to be able to plan a system and then to get valid results, you need to know what phase the HWS is on.