Emoncms adding feeds together?


I'm just trying to get Martin's 3 phase setup (3 EmonTX connected via I2C) to work, but I have a problem when calculating feeds on Emoncms:

Martin's script sends power and voltage, I want to have current too. First I log the power value(s) into a feed, then I divide it by the voltage to get the current (logging it in a feed too). After that I multiply it again to get the power again and calculate the kWh/d. Now my problem: I want to add the 3 power values of every phase together to get the total power of the system, but how can I do that without affecting the calculation of kWh/d (for each phase) because i is possible to add another feed but not to subtract a feed.
 Is it possible to save a value somewhere and get it back later in the calculation of a feed? If yes, how can this be done?

I've added a screenshot of the input. The normal calculation power to feed, current to feed, power (kWh/d) is done in 1-7, with 8&9 I want to add up the power values of phase 2 & 3, to get the total value for the total power feed.


I think I will edit the firmware for the EmonTX too to get only current and voltage, so there is no need for the EmonTX to calculate power and for the Raspberry to divide it again to get the current values out f the power values. This would save a lot of calculation => faster execution, maybe lower power consumtion on EmonTX.

MartinR's picture

Re: Emoncms adding feeds together?

Wouldn't it be easier just to add Irms to the emonTx payload? It's calculated anyway with the call to calcVI().

The current you are calculating will only be equal to Irms if the power factor is 1

Good to hear that you have the hardware working.


TrystanLea's picture

Re: Emoncms adding feeds together?

The Power to kWh/d input processor returns the power value unchanged. So it should be possible to do something along the lines of:

Log to feed: power1

power to kwhd: kwhd1

+ input: power2

+ input power3

Log to feed: totalpower

power to kwhd: totalpower_kwhd

jb79's picture

Re: Emoncms adding feeds together?


@TrystanLea: Perfect, that would simplify my calculations a lot. Meanwhile I also found out that the power to kWh/d doesn't change the power value. But is it possible to add "- feed xy" to one of the following versions of EmonCms?

I could also be useful to update the documentation of the input processing: http://openenergymonitor.org/emon/node/297. Some of the functions there are still not documentated.

Another question: Is there a version number in EmonCms anywhere or is the modular version the same as in the middle of December (no changes since the release)?


After reinstalling the software on the 3 EmonTx several times and also testing some single EmonTX scripts it seems that is is working stable most of the time. But there are some problems to solve for me:

1.) Calibration: How to get the correct phase calibration values?

2.) sometimes I get values of about 65xxx from one of the slave boards, that destroys every measurement because if they were real, the power has to be about 100kW at that time. In a graph I can only see this spikes, the rest is at about 2-3% of that => can't be seen. So I think there has to be a "filter" on the master-EmonTX to eliminate these high values, maybe by sending the old, plausible values until the actual value comes back into a plausible area, lets say about 8kW per phase that would perfectly fit the value of the main fuses in my house (I think they are 35A)

3.) Testing the Range of the EmonTx because 1 single version will be mounted into my gardenhouse, 25m away from the house. Maybe it can help to put the Raspberry in the attic to get a better connection...


My test setup hosted on the RaspberryPI:


On the test-dashboard you can see the actual power consumtion of my house, but 2 voltage sensors are missing (ordered in shop, allready on the way). So there is only one phase measured by the 3 phase 3xEmonTx system with Martin's firmware. 3 additional CTs will be installed soon for measuring the power consumtion of the heat-pump system, option for 3 phase PV system with another 3 CTs in the future.

The second system has temperature sensors. Sensor 1 is hanging outdoor under the office window, sensor 2 is under the office table (PC), sensor 3&4 are also indoor next to the window. CT (Solar) is hanging on the halogen desk lamp (values are wrong because they're calculated for 230V but the lamp has only 12V...).

MartinR's picture

Re: Emoncms adding feeds together?

I don't think any of your problems are related to the 3-phase part of your system, they're just general emonTx  issues which have been answered in other posts.

The 65xxx values are correct, they're just small negative values.There was an old version of  EmonCMS that didn't handle negative values correctly.


TrystanLea's picture

Re: Emoncms adding feeds together?

Jurgen, Emoncms has only just been updated since the middle of december (2 hours ago). best way to check is to look at the github repo lists the last time it was updated there https://github.com/emoncms/emoncms

We did discuss creating some form of version numbering a while back but Im no further with it im afraid.

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