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On my 3 -phase charger  the Amps are adjusted, using a raspberry, according to what is given as available on the energy meter of my solar plant.

On a sunny winter day I easily get the 11 KW my EV will take: 16 Amps.

But there are frequent cloudy days or low sun conditions with solar outputs around 3KW, when I cannot charge with 3-phase on 6 Amps without topping up with grid power, which I buy 3x my selling price.

It's very easy to add a relay, run by the raspberry, on the mains line, to on and off L2 and L3.

But how how will the EV take this?

Take the following with a rather large chunk of salt as I'm not an expert in the inner workings of the various EV charging standards or of the firmware that runs OpenEVSE. However I do have an OpenEVSE, have read the descriptions of the protocols provided by Chris, and have an EE degree.

My immediate thought would be to have the Raspberry Pi disconnect the pilot so that both the EV and OpenEVSE would gracefully disconnect and stop drawing power after a short time. Then after waiting a second or two, have the Pi perform the 1-to-3 or 3-to-1 phase conversion. This way neither device experiences a sudden change in the way power is delivered and the inherent protections / fault recovery mechanisms are left intact.

As long as you provide OpenEVSE power off leg-1, I don't believe it will "care" that you're disconnected leg-2 and leg-3 of mains power. Providing a pilot disconnect should be relatively easy as it's a low-voltage, low-current line, but I would suggest a small relay for this as well rather than trying to pass that signal through the RaspberryPi or a BJT/FET in some way. You don't want to really "mess with" the pilot signal, just pass it through or not.

Alternatively could achieve the same effect as disconnecting the pilot signal by leveraging the RAPI / MQTT interface available, depending on your coding skills.

I definitely agree, as long as I do not know beforehand how the EV system reacts to a phase conversion without disconnects, sending FS and FE commands between the phase conversions is the right approach.

OpenWB support such:

https://ph22dlvbri7bbqrgjm3yxfbw7q--openwb-de.translate.goog/main/?page_id=557

it will allow to range from 3 phase charging (22kw in example) to as low as 1.3Kw single phase (6A). I don't have the link handy but I read that they pause the charging during such switch - so guess that what Paul is proposing is reasonable.

I think their WB is inverter based, rather than Jgalea's approach regarding how to disconnect the 2 phases.

OpenWB can do such - I think Paul is correct reading their documentation it seems they pause the charging during phase shifting:

CP interruption to wake up the EV (some EVs “fall asleep” after some time without charging. If the PV charging is then started, the affected EVs do not start charging. The CP interruption animates the EVs concerned to reinitialize the charge without unplugging to have to)

Automatic switchover between 1/3 phases

The automatic switchover enables the number of phases used for charging to be set depending on the charging mode. This means that charging can be carried out with just one phase in PV mode. This enables fine control, low starting power (around 1.3kW) and, depending on the EV, up to 7.2 kW maximum charging power. If the PV power exceeds the maximum charging power during single-phase charging, the system automatically switches to three-phase charging.

Likewise, with Immediate Charging, if you want to go quickly, you can charge with 3 phases and up to 22kW (depending on EV and supply line).

* The option must not be used in conjunction with the Renault Zoe or other vehicles (e.g. the new Smart) with Zoe charging technology! If one of these vehicles should be able to be charged, the option must be selected when ordering. The switchover is deactivated on the hardware side, but can be reactivated later. The switchover works without any problems with all other vehicles.

If the Tesla plug is ordered, the plug supplied is not gray as shown, but blue and has the extra button. 

Thank you Stefano for information about how other people are managing 1to3 phase switchover.

I do not see how WB can do inverter based switchover.

Anyhow, my intent is to achieve this with OpenEVSE, as I am already using one, and I will be welcoming any feedback on this forum from other OpenEVSE users trying to do the same thing.

Paul is quite right: my EV, an ID3, ignores a switchover without FS/FE commands. It just goes on charging in the initially set phase mode.

I have been running node red scripts doing the switchover during the last 3 months, whilst at the same time using PV divert on the OpenEVSE.

It works but needs improvements..

In order to avoid cloud induced frequent relay switching I have tried adding  hysteresis, averaging, time delays etc.

This may be interfering with  what is already included in the OpenEVSE.

Getting this to work is a lengthy process as  many conditions have to be met: EV at home,EV needing recharging, clouds chasing each other, myself being available...there are few low PV power days at this time of the year in my area.

I have a PV battery in the system, which should not be discharged into the EV, but could be used to limit relay cycling. There also is a heat pump storing heat in a tank during daytime and not allowed to use the PV battery. Priorities have to be set and emergency operation made possible.

So it looks like the whole system has to be integrated,  the OpenEVSE set  in Normal mode and separately fed charging current values according to excess power.

After 3 years of testing and tweaking I now have a system which is operating properly.

The OpenEVSE Eco/Normal feature is not used.

The Evse is disabled and enabled for every changeover.

Three phase is allowed as long as available power rises above the threshold power, about 4200 watts, less than 3 times every 10 minutes. Changeovers, thus, reach a maximum of around 20 per car charge.

A car diagnostic tool does not show any faults, which it does when there are frequent power interruptions.

Changeovers lag behind power by up to half a minute due to a combination of polling period for 3 power meters, nodered flow inject interval, set delays in the nodered flow and car reacting time.

A normal mode is equally built in including delayed charging.

Graph 1 shows a charge beginning in 1 phase due to frequent clouds, and ending in 3 phase.

Graph 2 shows a day with fierce winds and running clouds: 1 phase only

On a Raspberry Pi I have nodered flows, MQTT and InfluxDB.

Grafana is used for reporting.

Single phase L1 power is measured by the Evse.

L2 power is measured by a Tasmota/Sonoff power meter.

L3 power is assumed to be equal to L2.

A Tasmota/Sonoff switch is used to trigger the relay switching on and off L2 and L3.

Power exported to the grid is measured by the PV system.

Commands are sent by the nodered flows to the Evse by RAPI over http.

Evse values are obtained from my MQTT server.

Although OpenEVSE has a well working solar divert feature, I am not using it as I need to integrate my solar battery and heat pump in the logic.