Keeping ZOE’s charger alive but not charging

ZOE falls in a deep sleep about 6 minutes after she’s closed up. I have written about this before in the context of resetting the BCB. For delayed charging under charger control this can be problematic: if you connect ZOE to an unpowered charger, i.e. one with a timer in its power line, she will fall asleep and nothing but opening the doors will waker her up.

However, my charger, a KEBA P20 has a control line where you can disable charging without powering it down. I use this for timed charging, which has somewhat complicated schedules in my country: economy rates are active at night and during weekends and during some bank holidays. Easter Monday (variable date!) being one of them. I was curious how the charger kept ZOE awake enough to start charging after hours in a disabled state.

Here is how the protocol works.

1. You plug in the cable. The car is still awake and detects the PP-PE resistor of the cable and locks it. The chargerpoint also puts a +12 volt DC through a 1K resistor on the CP pin, but this is not what makes the car detect the cable.
2. The car sees the 12 volt signal and signals the chargerpoint it would appreciate a charge. It does so by applying a resistor (882 ohms) between CP and PE. This drops the voltage from 12 to 6 volts, which is detected by the charger.
3. If the chargerpoint is enabled, it will change the signal to a square wave pilot signal. The positive pulse width indicates the maximum current per lead the car is allowed to take. In my case it was 268 uS, corresponding to 16.08 amps. It will also close the contacter, connecting the car to the grid.
4. The car recognizes the pilot, closes it’s own contactors and starts charging.

If however the charger is disabled, it will not close the contactors and it will not change the CP signal to a pilot, but just keep it at a steady 12 volt, minus the drop over the 1K resistor of course caused by the car requesting a charge. ZOE stays awake enough now to recognize the transition to charging later on. I am pretty sure you need to connect your car to the powered, but possibly disabled charger before she falls asleep.

Bottom line: if you have a chargepoint that cannot be disabled but you want it to do so, insert a relay in the CP line, common to the car side, NC to the chargepoint side. The NO side should be wired through a 1K resistor to +12 volt, which you need to find somewhere in the chargepoint. The chargepoint will not see the car being connected, the car will see the keep awake signal. As always, be very careful. Live wires close by.