Why does my EV refuse to charge even though the battery is not full?

This article covers the problems experienced with some EV's that occasionally refuse to charge when zappi is in ECO+.   

The car may charge for a short period but then stop charging even though the battery is full.   

This is known to happen with some versions of the VW eGolf and Peugeot e208.  Recently a similar problem has also been experience with the Porshce Taycan.

In this article:

• How do zappi and the EV communicate?
• How does zappi tell the EV to charge?
• Why would an EV refuse to charge, or stop charging early?
• Possible immediate changes to zappi settings
• Adjusting the Minimum Green Level (MGL)

How do zappi and the EV communicate?

The communications between the EV charger and the car are very basic - simply measuring a voltage on one wire (the Control Pilot) in the charge cable.  There are a number of possible states for the Control Pilot signal:

A - EV unplugged
B1 - EV plugged in, but Charger not ready to supply power
B2 - EV plugged in and Charger ready to supply power
C1 - EV plugged in and charging, EV charger wants EV to stop charging
C2 - EV plugged in and charging

How does zappi tell the EV to charge?

As soon as zappi is ready to charge the EV it will set the Control Pilot signal to state "B2".

At this point it is up to the EV whether or not to start charging.  It it wants to charge the EV will set the Control Pilot signal to state "C2" and zappi will immediately respond by turning on the output to the charging cable.

A change from B2 to C2 is initiated by the car

If zappi tries to charge (by going from state B1 to state B2) but the EV but it does not respond then it will report "Charge Delayed".

Zappi stays in state B2 which means that the car can start charging straight away if it decides to wake up (eg, if there is a timer set in the car)

A change from C2 to B2 is also initiated by the car

If zappi detects that the Control Pilot has changed from C2 to B2, this indicates that the EV has stopped the charge - ie the battery is full.

Zappi will show this as "Charge Complete

Again, the Control Pilot is left in state B2, which means that the car can start charging again straight away if it wakes up and asks for more power.  (eg if the charge is interrupted by unlocking when it was charging)
 

Why would an EV refuse to charge, or stop charging early?

Some customers report that the EV has stopped charging, even though the battery is not yet full. 

An example is one customer with a Porsche Taycan - In one reported incident the car should have continued charging - battery was only 41% full and zappi saying Charge Complete, so zappi is still sending the signal to the car to tell it to continue charging.  So the car is refusing to charge.

A similar problem occurs with the Peugeot e208 which only allows the charge to be interrupted ten times before the onboard charger blocks any further charge.  The onboard charger can usually be reset by unlocking the car, or it may be necessary to unplug the charging cable and then plugging it back in again.

The problem can often be resolved by ensuring that the zappi firmware is up to date and then adjusting the ECO+ settings

Possible immediate changes to zappi settings

One change to the zappi settings which has helped with the VW eGolf and Peugeot e208 is to adjust the ECO+ start/stop delay so that the EV keeps charging through short interruptions in the available surplus generation.  These vehicles allow the charge to be interrupted a number of times but then won't restart until the charger is unplugged and plugged back in again.

The starting point is to update the firmware to the latest version.

Then on the menu "Charge Settings - ECO+" a separate time can be set for the start and stop delay.  

Recommended values are:

• "start" delay = 30 seconds
• "stop" delay = 240 seconds

Adjusting the Minimum Green Level (MGL)

The MGL can also be adjusted to reduce the number of interruptions in the charge.

By setting this to 1% the charge will continue until there is less than ~14W surplus power available to charge the EV.  Extra power will be taken from the grid to keep the charge running