Controlling the wallbox via KNX: How to optimize self-consumption in one-family home

When building a new house, planning charging stations or wall boxes for electric cars such as a BMW i3, BMW iX xDrive, Porsche Taycan or Tesla Model S is very important. We design and plan the electrical installation for the power supply and data connections for almost every house construction. The background: The electric house, which is a house with a KNX infrastructure and its data lines and controls, fits perfectly with an electric car and its battery storage. The advantage of the KNX Smart Home: all the intelligence and control is already there.
However, the installation of a wall box without charging control is not particularly intelligent, since expensive energy from the power grid is also used to charge the car battery. The goal should therefore be to charge as much excess energy as possible from the PV system directly into the electric car battery. At the same time, the charge control should take place automatically in the background and follow a priority when other consumers in the house (e.g. stove, dishwasher, washing machine, etc.) are switched on.

We implement the following wishes with our KNX charging control:

  • Excess energy from the PV system should charge the electric car battery directly
  • Control of the charging regulation via KNX Smart Meter and KNX EibPC
  • 3 modes of charge control: time control, current limit and capacity specification
  • Control via touchscreen visualization or KNX button in the room
  • Integration of battery storage and grid feed-in (control/limitation)
  • Accurate meter for currents and voltages (house connection tap)
  • Consumption recording kWh
  • 400 volt charging station up to 11/22 kW with high power (3-phase 11 kW (3x16A) or 22 kW (3x32A)

Our example of controlling the charge control of a wall box via KNX shows how easy it is to optimize the charge control in the house. The picture below shows the KNX visualization with the Enertex EibPC, which is certainly getting on in years and still works well.

Wallbox control in the KNX visualization: Start/Stop at the push of a button with all information on currents, voltages and state of charge

KEBA KeContact P30 X-Series: KNX connection via UDP

  • Network via switch (master/slave network) 
  • Modbus TCP (external meter), UDP (status information for KNX)
  • configuration file
  • web interface
  • Load management for master/slave of several boxes (15)
  • Adjustable current limit
  • Current and voltage
BMW i3s Wallbox KNX Smart Meterjpg
On our wall box: BMW i3s for automatic charging
Wallbox Laderegelung KNX Smart Meter
Also on load: Mini Cooper SE
BMW iX xDrive 40: Charging at a Keba Wallbox with charging control via KNX

Charging control via Enertex KNX Smart Meter and EibPC

210128 Wallbox KNX Smart Meter Enertex
Test setup for charging control: Enertex KNX Smart Meter and EibPC for intelligent control of the charging current from the PV system on the roof.
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