Automatic Phase Switching

Note:  This feature is only available for three phase versions of the zappi running firmware version 5.300 or above

With version 5.300 we have introduced the ability for a three-phase zappi to automatically switch between single phase charging and three phase charging in ECO+ mode as the available local generation varies.  With this feature it is possible to choose how many phases zappi uses, on the Charge Settings -> ECO+ menu.

The options are

• 1 phase - zappi will only use one phase to charge in ECO / ECO+
• 3 phases - zappi will always use three phases to charge in ECO / ECO+
• Auto - zappi will switch automatically between one phase and three phases in ECO+ as the surplus local generation available varies.

The desired mode can be selected at the bottom of the Charge Settings screen:

Important

With "Auto" selected, zappi will do a short test charge when the EV is first plugged into check the charging capabilities of the vehicle.  When you plug the EV in to zappi it will start charging at full power with three phases.  If there is insufficient surplus generation available to support the three phase charge then power will drop to ~4.2kW (or ~2.8kW for a two-phase EV such as the VW e-Up) while the countdown timer times out.

zappi will then switch to single phase charging, after the phase switching delay. For your safety and to maximise vehicle compatibility this delay is 90 seconds and cannot be changed.  

If there is insufficient surplus generation available for a single phase charge (~1.4kW) then the countdown times will run again and zappi will then pause the charge until there is enough surplus generation available.

How does the auto switching work?

Once zappi has carried out the first test charge it will then track the surplus local generation, varying the control signal (the "PWM" value) to the EV to tell it how fast to charge.

Starting with a single phase charge the power to the EV will increase until the PWM as the surplus generation increases.  Once the PWM value reaches the maximum value possible for that EV (taking into account the detected EV type as well as the device and grid limit) then a 90 second countdown timer is started.   When that timer reaches zero then zappi will switch to three phase charging:

• the charge is stopped
• there is a 90 second "Phase switching" delay to make sure that the connected EV can safely be switched to three phase charging.
• the charge will then resume in three phase mode.

Once in three phase mode, if the available power drops then the PWM value will be reduced until it reaches the minimum allowed by the EV charging standard.   For a three phase EV it will still need ~4.2kW to continue charging, with the surplus generation being topped up from the grid.   At this point zappi will show "Importing" on the display, and the ECO+ Stop time will start to countdown.

When the ECO+ Stop timer reaches zero zappi will switch back to single phase charging

• the charge is stopped
• there is a 90 second "Phase switching" delay to make sure that the connected EV can safely be switched to single phase charging.
• the charge will then resume in single phase mode.

The interruption in the charge can upset some EV's which will stop charging if the supply is interrupted too many times.  If zappi reports "Charge Delayed" after phase switching then this may be the problem and you should continue selecting single phase or three phases charging for ECO+ and not the "auto" feature.

What about the Minimum Green Level (MGL)?

The MGL setting affects the power taken from the grid when there is insufficient surplus generation available.   This will have an impact on the switch from three phase to single phase charge. 

Although there may be some circumstances where this is desirable our advice is that MGL should be left at 100% when the auto phase switching setting is selected.

Automatic Phase Switching and the Neutral Limit

The automatic phase switching does not, currently, always work when a Neutral Limit is set.

For instance - if the Neutral Limit is set to 20A and the Device Limit is set to 32A then the current supplied to the EV will be limited to 20A.  At this point zappi still thinks that the single phase current could be increased further as the Device Limit has not been reached.

We're still working on this particular feature but as a workaround, reducing the device limit to below the Neutral Limit (eg 16A) will ensure that the automatic phase switching takes place.  If this setting is not available then please continue to manually select single phase or three phase ECO+ charging until we release a new firmware update.