Setup Emonpi in Japan (split phase similar to North America)

Living in Japan (with split-phase similar to North America) and trying to setup a smartEV charger using an emonpi and OpenEVSE.

  1. If I am only interested in monitoring import/export from the grid (not how much solar I am making), do I need the emonPi solar option with a CT to monitor solar generation from the inverter? I mean- can I simply use 2 CTs on my mains to monitor if buying or selling (does the CT monitor which direction the current is flowing)?

  2. If I do need the CTs on the solar to monitor import/export, then limited to the 2 CT inputs on the emonpi. From what I read on the ‘Use on North America’ page, I need to parallel 2 CTs for the mains (split phase) and use (maybe) 1 CT for the solar.

  3. If #2 is my option, then the easiest to understand setup is at:
    https://community.openenergymonitor.org/uploads/default/optimized/2X/b/b21a65e45a094cadd17df58d763351594c646ddc_2_690x388.jpeg

BUT, I searched quite a bit and unable to find a 100A:0.5V split core current transformer.

Can anyone recommend which CTs to use for the mains for a split phase system. Hopefully a pair of CTs that may not need to be calibrated and/or modified (burden

***************Useful post from Thomas Dunbar ***********

I used an EmonPi and three CTs. (two WC3-100-MV500 and one WC1-025-RV001)
For grid sensing, I used two 100A:0.5V Wattcore split core current transformers. I installed them per Figure 3a and connected them per Figure 5C on the “use in North America” page linked to earlier.


  1. This may also be an issue. Is this something I need to check?

***************From same post from Thomas Dunbar ***********
“When I ordered by EmonPi, I said I didn’t need the default CT and in return, they removed the surface mount resistors”


Welcome, Paul, to the OEM forum.

The “bundles”, e.g. the solar option, are just that. If you’re not interested in knowing the contribution from the P.V., you can indeed use the two c.t’s on your two incoming feeds, and provided you also have the a.c. adapter, you can determine the direction of power flow.

That is the other way to do it. You lose the ability to know the contribution of the two incomers separately, you gain the ability to know the P.V. input.

This is one reason why we are moving to 0.333 V output c.t’s for the emonTx V4. C.T’s that are capable of 1 V or 1.1 V output with or without an internal burden are hard to find.
Another option for the P.V. infeed might be to count pulses, if you have a generation meter with a pulse output - optical or S0. That’s not an option for your main supply, because generally you get no usable indication when exporting energy.
And yet another - if your generation meter has a data output that’s usable, that can be sent to the emonPi, but it will require an interface to connect to a USB input on the emonPi.

If you have c.t’s with an inbuilt burden, i.e. the output is quoted as a voltage, then you must NOT have the burden inside the emonPi. The Shop is always open to negotiation, so they can remove the burden resistors if you ask. There are also holes to replace with wire-ended resistors of a different value, should that be needed. If asked, The Shop might be able to do this for you.

Thank you for the advice. I used the 2 CTs that came with the emonpi from the shop and connected to CT1 and CT2 inputs on the emonpi. Appears to be working fine for checking import/export.

I initially set the emonhub.conf to 100 V as Japan is 100 V but realized this is a switch setting, not the actual voltage.
After setting too 110V, all worked OK.
emonhub.conf calibration=110v
So I am guessing that the USA AC-AC Adapter (for 120V) works OK in Japan with 100V outlet.

Next is to set up the EVSE charger.

To monitor solar generation, seems it will be easier to use the EmonTX (when the latest version is out.) rather than the emonpi. The emonTX has 4 CT inputs, so I can use 2 for the solar and 2 for the mains (split-phase) I hope.

Yes, that should be OK.

If you’re using the emonTx V3.4, No.4 c.t. has a different burden (120 Ω) so it’s derated to 16 A when used with the YHDC SCT-013-000. You can convert it by adding 27Ω in parallel with the 120 Ω burden on the pcb.

The emonTx V4 will have 6 inputs, BUT these aren’t directly compatible with your YHDC c.t’s (yes, I know, but it’s better in the long run). You’ll need a separate burden (6.66 Ω, 0.1 W, or 3×20 Ω in parallel) to convert the 50 mA output of a YHDC c.t. to 0.333 V. You could use the emonPi on one pair and an emonTx on the other - the potential problem is the readings won’t be synchronous, so the sum or difference won’t necessarily be correct.

Thanks. I’ll order the emonTx v.4 when it becomes available. Will purchase new CTs that are shipping with the emonTx v.4 so I don’t have to worry about making any changes to the hardware/software (do-able, but a bit of a learning curve).

Next task is to get my emonPi working with the OpenEVSE WiFi EV Charging Station so I can charge my EV with 100% solar! Fun stuff.