OpenEnergyMonitor Community

OpenEVSE DIY Tethered 3-phase

Hi Glyn
Finally I found the problem.

I need a resistor between Ground and PP wire, car side.
PP is not connected to the main board.
In my case the cable is 6mm2 = 32 A and my type 2 plug is also 32A.
The resistor to work with this intensity must be 220 Ohms.
I put a 240 Ohms because I had it at home.
It charge !!! :slight_smile:

Now the problem is the firmware energy calculation in kWh.
Look at the print screen. The charging current was between 16 and 17 Amps all the time in 3 phase. Voltage was around 400V. Thats about 11kW for 1h41 min. The energy must be around 18,7 kWh and no 2,62 kWh as represented.

Can you arrange that calculation please?
Kind regards


Ah, that’s good to hear. Most EV connectors come with the resistor pre-installed. This is the first time I’ve heard of a connector being supplied without a resistor. Did you make up your own cable? For anyone else following this thread here is some more info on resistors in charging cables:

This only applies to Type-2 cables, Type-1 cables don’t have a resistor at the car end, at least not connected as standard between PP and GND. A resistor is connected via the switch on the connector which signals the EV to stop drawing current when the switch is pressed :


Enabling #define THREEPHASE in open_evse.h should enable three-phase energy calculation. This should be enabled as standard if you are running three-phase FW. Could you show me a screenshot of the openevse UI showing the controller FW? It should end in .3P if it is indeed running 3ph firmware.

Hi Glyn
Yes I did my own cable and installed a type 2 plug.
how I do that?:
Enabling #define THREEPHASE in open_evse.h should enable three-phase energy calculation. This should be enabled as standard if you are running three-phase FW. Could you show me a screenshot of the openevse UI showing the controller FW? It should end in .3P if it is indeed running 3ph firmware.

the FW you send me to install is openevse-3ph.hex in may 2019

Apologies, I must have made a mistake. I’ve just recompiled a special OpenEVSE FW with THREEPHASE enabled. The firmware version is 5.1.0.EU.3P. See attached:

firmware.hex (85.8 KB)

Sorry Glyn
I just uploaded the new firmware and the calculations are again for monophasic, not triphasic (see pictures attached).
Power 3p = 400V x AMPS x SQRT(3)

Are you saying that is what the calculation is, or what it should be?

If your line-line voltage is 400 V, hence the line-neutral voltage is 231 V (400 ÷ √3), the total power is 3 x VLN × IL = 3 x VLL × IL ÷ √3 = VLL × IL × √3

As you can see on the screen shots the calculated power is 230V (V line-neutral) × I = power in monophasic system and I’ve a triphasic.
In the calculation formula it’s missing cos(FI). Do you know the cos (FI) value for this charger ?

Can you please implemented the following formula to the 3 phasic system FW ?
Power = 400V x I x sqrt(3) x cos (FI)

This is how threephase energy is calculated:

- P(3ph) = V(LN) * I * 3
- V(VL) = 230V (line to neutral voltage)
- V(LL) = V(LN) * √3 = 230 * 1.75 = 400V

Hi Glyn
Thanks for your patience.
Please take a look of my screen shot
Intensity = 12.76 A and Power = 2935 W
That means Voltage = 2935 / 12,76 = 230 V, and not 230V x 3
Then your software to calculate the energy is correct but there is a bug:
THREEPHASE is not active in the firmware and it continue to calculate as a Monophasic system.
Kind regards

Glyn I have a second question:
In the formula we miss COS (FI)
Power = Voltage LN x Intensity x 3 x COS (FI)
do you know the value of COS (FI) in this charger?

probably TREEPHASE it’s not defined at open_evse.h


Please try again with the FW attached, I have explicitly defined THREEPHASE

openevse-3ph.hex (85.8 KB)

If this doesn’t work you could try building the FW yourself. Three-phase calculation works for the EmonEVSE.

Hi Glyn
Thanks for your patience
Now it works
Thanks a lot

Fantastic! Very sorry, for all the hassle. The mistake must have been at my end.


I know that this is an old thread, but have a question about 3-phase installation and setting the THREEPHASE constant. Is it possible to change it on the fly? For example have some toggle in the web ui to be able to switch it to either 1-phase or 3-phase? Basically I have 2 cars (one has single phase charger and the other has 3 phase charger) and I would like to be able to switch the param on and off based on which car is currently charging. Ideal solution would be to add one more current meter (on L2 or L3) so that the software knows automatically if I’m charging 1 or 3 phase car.

Thanks in advance.

I’ve just had a 3 phase EmonEVSE installed and despite the firmware being reported as, I too see only single phase energy calculations both in the UI and the MQTT feed to my EmonCMS.

I’m also unsure therefore if the PV divert is going to be observed correctly on the grounds that the value I’m returning about grid import/export is for all three phases, not just one.

I see the reference in this thread to the constant THREEPHASE being defined, but no detail on how to set this? I would also expect that to have been set correctly in this firmware?

The OpenEVSE UI displays real-time charging current, which is the same for both single and three-phase e.g 32A 1P = 7kW / 32A 3P = 22kW. However, the kWh/wh reported on the OpenEVSE UI and Emoncms will show the correct energy calculation for 3P.

Solar PV divert is based on current, therefore should work the same for both single and three-phase.

Hi Glyn,

thanks for replying.

I get the 32A bit. But on the emonCMS, there is only one energy calculation and it only shows the power for a single phase on my 3 phase unit. Please see attached screenshot showing the consumption at circa 3.7kW, the unit is actually charging at 11kW. This is the reasoning for my query.

I’ve had to add the energy feed to each of my 3 phase monitors to get my total usage correct.

Thanks for the screenshot, I can see the issue. The charging power shown on Emoncms is calculated in Emoncms input processing, the amp current Input is multiplied by 230V to display the power, this should be multipled by 3x for three-phase.

To change this, open up Emoncms Inputs and click the spanner icon next to openevse ‘amp’ feed:

Then change 230 to 230V x 3 = 690

The power will now be displayed correctly. Alternatively, for more accurate power reading, you could multiple by emonPi VRMS feed x3

The ev_energy Feed should be correct for three-phase since this energy is calculated on the openevse.

To make this easier for new users, I’ve added a three-phase device template which will do this automatically, but since you already have your Feeds setup it’s probably easier to adjust manually. Thanks for reporting this issue.