All homes/businesses attached to the electrical grid have some limitation to the amount of current they can import from the grid. When charging one or more EVs, these can consume significant current so it is important to ensure that the total grid current does not exceed its limit. Hereby we not only look at the current of the EV(s), but also at the current being used by other appliances in the building. In case of a Smappee EV Wall, the required hardware to measure the grid is included. In case of an EV Wall Business or EV Base, a separate Infinity installation is needed to measure the grid.
To set your maximum grid current, you can use the 'Smart devices' card in the dashboard, or if you prefer to use the app, go to 'Settings' - 'Your Smappee monitors' - 'Load configuration' - 'Grid' - 'Maximum current'. For more information on how to set the max grid current, see this article.
It's important to keep in mind that we always use a 10% safety margin in order to prevent overloading of circuit breakers. So, if there is 63 A available on the 'grid', our overload protection will adjust the charging speeds of active charging sessions in order to prevent currents higher than 56.7 A on the grid connection. This safety margin helps us ensure that we never trip the circuit breaker, even if there is a short peak in power usage from other loads within the circuit.
The measurements and the algorithm work per phase, but the communication protocol that almost all EVs use at the moment (IEC 61851) only allows us to send 1 setpoint to the EV. It is not possible to send a different setpoint for each phase. We also cannot tell the car how many phases to use; we simply provide 3 phases and the car will choose whether it uses 1, 2, or 3 phases. At the start of a charging session, we will very briefly (only a few seconds) let the car draw full power (within the limits of the installation) in order to determine how many phases the car uses and what its maximum current is. The algorithm then remembers this information for each active charging session. This is important because, let's say that there is a single-phase EV that uses only L1, its charging speed only needs to depend on the available current on L1 and the measurements for L2 and L3 do not need to be taken into account. Note that, if you have more than one charging station, it is beneficial to use phase rotation during installation. Read more about phase rotation here.
The available current is divided among the active charging sessions, but there may be cases where there is not enough current available to provide the minimum of 6 A to all connected EVs. In this case, some sessions will need to be paused until more current is available. Which sessions are paused is based on priority. It is possible for the charging station owner to assign priorities to certain usernames (if 'Scan and charge' is used) or to certain RFID tokens (if 'Swipe and charge (free)' is used). It is also possible to assign a default priority to unknown users. By doing this, you could for example assign a lower priority to employees than to visitors. This might be useful because employees will probably be parked for a longer duration than visitors, so you might want visitors to be able to charge faster.
For the Smappee EV Line, the overload protection runs in the cloud so it is important that the charging station and the Infinity installation (where relevant) have a reliable connection to the internet.