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Been succesfully using one VAC and 3 CT:s on one emontx board about an year now. Seems to be fairly accurate. Personally dont see the need for 3 ac measurement points - but this may vary depending on how good quality your mains grid is.

Biggest problems have had with nanode rf as gateway but after changing to raspberry as RF gateway to ethernet/emoncms.org everything runs smoothly without hangups.

My full setup includes now 4 x emontx with 7 x CTs, 3 x funky temperature nodes and raspberry with RFM12B module measuring 3 phase mains, 2 heatpumps, room temperature, consumption of hot water boiler and not to forgot mk2i solar to hot water system.

So a simple setup could be e.g.

1x emontx with RFM12B

3x CT

1x AC transformer

1x raspberry with RFM12B module as gateway from radio signal to ethernet (+ethernet cable to your router)

1x psu for emontx

1x psu for raspberry

this way you would have an expandable radio network to add e.g. funky sensors as temperature nodes etc. in the future.

Personally dont see the need for 3 ac measurement points - but this may vary depending on how good quality your mains grid is.

Are you "doing the maths" to deduce instantaneous V for the other two phases, or running them in "current only" mode?  

Remember, V gets measured not just to determine its amplitude, but also to allow real power to be measured when I and V are out of phase due to reactive loads.  So each I reading needs to be multiplied by the instantaneous V reading for that phase.

Come on - its year ago when installed the standard 1 vac + 3 ct emontx script which seems to be accurate, dont remember how it is implemented, do recall there is a writeup on this board about 3 phase setup and script where operating principle is explained.

Dont see how one phase could be misaligned so badly that it would effect measurement accuracy, we seldom have reactive power devices din house like high power motors except vacuum cleaner, in theory one phase voltage could be +-10% but din reality seen only an odd volt here and there.

Dont see how one phase could be misaligned so badly that it would effect measurement accuracy

I didn't mean to suggest that.  I'm sure your 3 phases are rock-solid 120 degrees apart.   What I meant is that if you're trying to measure real power, you need to multiply I x V all along the sine wave, many times per cycle, and it would only make sense to use a V reading that corresponds to the phase belonging to the I reading.  As you say, if you're not worried about accurately measuring reactive loads,  there is no need to do that.  

yep - here is the link in case not read already how the standard script is implemented if i remember correctly...

http://openenergymonitor.org/emon/buildingblocks/3-phase-power

"If access to measure the voltages of the three phases is difficult, or you do not want to add extra hardware or use 3 emonTxs, then it is possible to measure the voltage on one phase and use this to derive an approximate value for the voltages on the remaining two phases. The method relies on the assumption that the voltages will be relatively similar and the phase disturbances small — though as we've seen above neither of these are necessarily always the case. If the power system is reasonably well balanced (which it should be), it is likely that this method will nevertheless be more accurate than simply relying on a nominal assumed voltage and power factor.

The principle is to sample the voltage of the first phase at intervals (as per the normal sketch and library routines). The measured voltage is used immediately to calculate the power etc. in the first phase, but at the same time stored. Then, ⅓ cycle later, the value is retrieved and used with the current measurement of the second phase to calculate the power there, and again ⅓ cycle after that with the current measurement of the third phase to calculate that power."

dBC, have you tried this 3phase emontx script or whats the critisism towards strategy chosen ? I found it fairly accurate and very easy to set up.

dBC, have you tried this 3phase emontx script

Nope, I don't have 3 phases or an emontx.

whats the critisism towards strategy chosen

None at all.  I was merely trying to understand what you used for V for the other two phases, and your last posting clarified that, thanks for the pointer.

Hey guys, thanks for helping. Nowadays I am using a The Owl Cm119 connected to my linux server, but I read the total amount of energy used in every 3 phases. I need usage statistics for every phase, without adding them. I am not sure, but I should get 3 different statistics graphic, and I don't know if that 3 CT + 1 emontx give me that information or the add of the 3 phases as the Owl meter does.

Sorry for my English, hope my explanation is quite good to make you understand what I want to do. So, my final questios if what should I buy to get independent reading from every phase:
Option a) 1 x emontx, 3 x CT
Option b) 3 x emotn, 3 x CT (one per every phase)

Thanks!

Option a) 1 x emontx, 3 x CT --> you also need one AC transformer
Option b) 3 x emotn, 3 x CT (one per every phase) --> you also need three AC transformers

for both options you also need a gateway to ethernet like RFM12B+raspberry or someting alike.

You can get usage statistics for each phase with both options, below is a log from my option a) i.e. 1xemontx + 3xCT + 1xACtransformer

http://emoncms.org/dashboard/view/3phase

The bottom one (phase 1) has a 1.2kW solar system and mk2i connected there so you can see that operational too. Other two phases have fairly constant loads from equipment like toaster, washcing maschine, tumble dryier etc.

Dear Petrik. Thanks for reply. Yes, I have in mind I need the AC transformer, just focused on the differences, all the gateway, raspberry,  lcd... are the same, just the emontx is the difference.

Can't see anything on your log... maybe wrong url?

Could this be the reason: Internet explorer is not really compatible with emoncms.org, maybe you could try firefox or google chrome as browser.

I use chrome, and i get a black screen. I have tried something and I think I have the correct url:

http://emoncms.org/Petrik/3phase

Is this one the right one? Seems so. It seems to show the real time V, but the graphic shows nothing. Nice example, I will try to get something similar. Thanks!

Sorry, Senano, that URL works for me in Chrome and Firefox, so the problem is your end.

If you want to measure 3 phases, voltage and current, you could add to the emonTx. There are two unused inputs, AIO4 & AIO5, available on the pcb (see http://openenergymonitor.org/emon/emontx), and if you repeat the components around AIO2 (R11, R12, R13, R14 & C10) on stripboard or similar, you can have 3 voltage inputs and 3 current inputs. You will need to make some changes to emonLib too, to use the different voltage inputs.

Ok, it must be my problem.

Well, I have ordered my kit, hope it arrives soon. However, making changes to emonlib afraids me a bit, hope this project doesn't get very hard...

Don't worry, there are plenty of people here who are willing to help you.