240v power direction

    I have just found this Forum and I am very interested in developing an Energy Monitor to control PV and Grid power in an eco house.     I have been experimenting with Hall effect clamps and my main problem is detecting which way the power is flowing - i.e. am I exporting or importing.  

    I see from your display pictures that you have a clear + or - indication of power flow direction.

   Having looked through most of the pages of this site (but I have not studied the software) I do not see how the OpenEnergyMonitor Arduino system does it.   Does a CT sensor behave differently from a Hall sensor and give a distinct directional output, or do you compute this from voltage/current phase angles via your mains transformer ?

    I have been playing with digital and mpu systems for years but am not well versed in 240v phase angle details.






TrystanLea's picture

Re: 240v power direction

Hello, nice plans!

There are two ways you can sense direction

1) Using a AC voltage adapter as in the Mains AC v.3 circuit.

2) If your measuring PV output and the house power consumption then we can infer direction:

Import = house - pv output. 

When import is negative it is exporting.

All the best



Paul Reed's picture

Re: 240v power direction

 You might like to see my project which acheives your objectives. I used Trystan's No2 because it gives you greater flexibility in the home wiring circuit. (seperating the immersion power circuit from normal power usage to prevent hysteresis).

I also post the readings to Pachube so I can check on generation/usage/efficiency.

faizan's picture

Re: 240v power direction

I am new to the open energy monitor,have just started the project with my SCT-013-030.as this kind of CT has the inbulit burden resistor i am not using any burden resistor.

​My problem which i am facing is with  100W bulb i am getting ct output of 14mV and i can't give it directly to my atmega 328.any suggestion on how to amplify these 14mV to my controller level.

​The other problem is, arduino is not available here can i form my own board with Atmeg 328 and other components.any suggestion Plz!

TrystanLea's picture

Re: 240v power direction

Hello faizan

The circuit you need to interface a CT with an atmega 328 can be found here:


and yes it will work if you build an atmega based board, it does not have to be an arduino.

izyte's picture

Re: 240v power direction

Hi Paul,

Your project is exactly what I am also looking for. Do you mind if I ask for the schematic diagram which shows discrete components attached to Arduino circuit. 

Thank you very much.

Robert Wall's picture

Re: 240v power direction

See "Building Blocks" for the basic theory and the emonTx Shield circuit diagrams on the Wiki for practical circuits.

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