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General info

Several parameters are needed to estimate time spent at charging stations and minimize overall Estimated Travel Time (ETT).

Charging curve

A function that maps State of Energy (SoE) to maximum charging power at that SoE that is used to calculate charging time. Charging time calculation assumes that the battery is already preconditioned to an optimal temperature for charging.

The charging curve is specified as a piecewise-linear function: for a specified power at a given SoE, linear interpolation is used between that SoE and the next specified SoE in ascending order. The curve is defined by 2–20 pairs of SoE and corresponding power values, with an entry for 0 kWh SoE being mandatory.

Charging curves vary significantly across vehicles, depending on factors such as cell type. For accurate charging time predictions, provide a curve based on measurements rather than relying on a typical curve. If the charging curve is unknown from measurements, use this typical curve:

  • 0% SoC: 35% of peak power
  • 5% SoC: 90% of peak power
  • 10% SoC: 100% of peak power
  • 35% SoC: 100% of peak power
  • 50% SoC: 90% of peak power
  • 70% SoC: 50% of peak power
  • 100% SoC: 5% of peak power
Example of a piecewise-linear charging curve for an 80 kWh battery with 250 kW peak power

Example of a piecewise-linear charging curve for an 80 kWh battery with 250 kW peak power

Note: For compatibility reasons, the Online Routing API also supports a piecewise-constant form, which is the default there. Nevertheless, we recommend specifying a piecewise-linear curve.

Charging connectors

Charging connectors define the physical and electrical specifications for vehicle-to-station connections. A vehicle can have multiple connectors, for example, separate AC and DC connectors, or multiple DC connectors to model different power levels at different voltages.

Station selection

The following parameters determine which charging stations are compatible with the vehicle:

  • Plug types: List of connector standards supported by the vehicle (e.g., IEC 62196 Type 1, IEC 62196 Type 2 CCS, CHAdeMO). Used to filter stations that have at least one matching connector.
  • Current type: Charging current type, AC1 (single-phase AC), AC3 (three-phase AC), or DC. Must match the current type of the charging station.
  • Voltage range: Optional voltage range for the connector. Used to select the correct charging mode when the same plug type supports different power levels depending on station voltage. For example, a vehicle that charges at up to 100 kW on a 400 V station but up to 350 kW on an 800 V station.

Effective charging power

Once a compatible station is found, the power actually delivered to the battery depends on both the station's capabilities and the vehicle's constraints. Three parameters set upper limits on what the vehicle can accept from a station:

  • Maximum power: Upper limit for the charging power accepted by the vehicle. The available power is capped at the minimum of this value and the station's rated power.
  • Maximum voltage: Upper limit for the charging voltage. The resulting voltage is the minimum of this value and the station's voltage.
  • Maximum current: Upper limit for the charging current. The resulting current is the minimum of this value and the station's current.

The available power at the station is derived from those constraints. Two further parameters determine the effective charging power used in the charging time calculation:

  • Base load: Power drawn by on-vehicle systems during charging, for example, battery thermal management or auxiliary electronics. Subtracted from the available station power before applying the efficiency factor. Typical values are 0.1–0.5 kW for AC and 0.4–1.0 kW for DC charging.
  • Efficiency: Fraction of the power that reaches the battery after losses in the charging path. Scales the lower of the maximum charging power at the current SoE and the available station power after subtracting the base load (see formula below). AC charging involves an onboard AC/DC converter with typical losses of around 10%, so values around 0.9 are typical. DC charging bypasses the onboard converter, so efficiency is typically close to 1.0.

The actual charging power at a given battery level is:

P(SoE) = efficiency × min(curve(SoE), P_available − baseLoad)

The time required for charging to a certain target SoC at a given charging station is then determined by integrating the effective power over the SoE range. The total time at a charging stop additionally includes the charging time offset, a fixed overhead for plugging in and initiating the session.

Product-specific information

For detailed information on how to configure charging parameters for specific products, refer to the following pages: