Zaptec Pro chargers support the legacy wake-up mechanism described in section A.5.3 of IEC 61851-1. This article explains how the wake-up mechanism works in Zaptec Pro chargers, particularly in scenarios like pre-heating for electric vans and trucks.
How Zaptec handles charging and wake-up requests
Zaptec Pro chargers are designed to manage power allocation dynamically through cloud-based coordination. Here’s how the system behaves during and after charging sessions, including its support for the wake-up mechanism:
Post-charging state: Standby with power signal active
When the car has completed its initial charging session, the charger pilot singal (PWM) will stay ON (in state B2) unless:
- The station operates in standalone mode.
- A command from the cloud disables charging.
- An error interrupts the process.
Resuming charging: Pre-heating or similar requests
When the car signals a need to resume charging (state C2), the process unfolds as follows:
- EVSE transition to C1: The charger immediately transitions to state C1, indicating to the car that power isn’t available yet. This gives the system time to request power allocation from the cloud load balancer. The charger does not close the contactor in this case).
- Power allocation: Once power is available, the charger transitions to state C2, closes the contactor, and charging resumes.
This typically takes only a few seconds but can take longer if power isn’t available immediately (e.g., due to high building power consumption).
Key state transitions
- B2 → C2: Car signals a need for charging (e.g., for pre-heating).
- C1 → C2: Power is allocated; the contactor closes, and charging should resume.
- C2 → C1: Charger requests power from the load balancer.
If the power request is successful, the charger returns to state B2 or C2, depending on the car's response.
Zaptec’s wake-up mechanism
If the car does not initiate charging after transitioning from B1 → B2, the charger triggers a wake-up sequence:
- The pilot signal is temporarily turned off, cycling through the states: B2 → B1 → F1 → B2.
- If the car still doesn’t respond, the EVSE takes no further action.
In most cases, this indicates the car no longer needs to charge (e.g., the battery is full). However, if the car requires charging for features like pre-heating and doesn’t respond, this may result in the feature not working as intended.