Charging with Session Targets

Setting Session Targets

eDRV provides developers the ability to start sessions in a fire and forget mode. This means that eDRV's session intelligence takes care of the post session monitoring for you in specific use cases, allowing you to shape the session once at start time.

You are free to design sessions in any combination of the following targets:

  • Energy (kWh)
  • Time (Minutes)
  • Money (Amount)
  • energy_start_time (UTC time)
  • energy_stop_time (UTC time)

For e.g. you may choose to start delivering energy within a session at 6Pm and have it stop when 30kWh has been delivered.

Let us go through each of these available targets in a little more detail.

Energy Target

Energy (kWh): E.g A session is started via a POST /sessions API call with an E kWh limit.
eDRV attempts to stop a session when session.metrics.energyConsumed >= E*1000
(No default session energy target)

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Use Case: Session with an Energy Target

When charging a fleet delivery vehicle, refuel the battery with the expected energy required for a round trip delivery.

Time Target

Time (Minutes): E.g A session is started via a POST /sessions API call with a T minutes limit.
eDRV attempts to stop a session when session.metrics.energyPeriod >= T*60.
(Default session time target is 12 hours)

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Use Case: Session with a Time Target

Where operators prefer to discourage drivers from squatting on a connector.

Cost Target

Money (Amount): E.g A session is started via a POST /sessions API call with a $M limit.
eDRV attempts to stop a session when session.cost.amount >= M
(No default session money target)

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Use Case: Session with a Cost Target

Prepaid EV charging, where the driver has paid for $M of charging.

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Accuracy of Session Target Detection (Energy, Time, Cost)

Please note that the chargestation sends energy reports every 30sec-1min to eDRV and it may take another 30seconds for the chargestation to respond to a session stop command from eDRV.

Because of this delay, consider adding some padding to the values when setting targets (Energy, Time, Cost) for a session. Most of the real-world charging sessions last for hours at a time in which case adding a couple of minutes (time) or 0.5 kWh (energy) padding to your targets may be advisable.

When testing with session targets with very short sessions (e.g. 2 minutes) please look out for unexpected behavior.

Energy Start Time

energy_start_time (date-time): E.g A session is started via a POST /sessions API call with a 2022-02-07T12:00:00.000Z energy start time.
Although the session may have started earlier, the charge station starts the energy flow to the EV at UTC time = 12:00.

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How to use Energy Start Time or Energy Stop Time

Session start_time or stop_time do not work if the session does not start (i.e. session.started= true)
For e.g. if the driver forgets to plug in the cable, the session will not start and the start_time target will fail (we cannot break the laws of Physics).

We recommend that you build your driver facing application UX as follows:

  • Request the driver to first plug in the cable
  • Detect cable plugin via chargestation.connector_status.updated webhook
  • Use /session POST with start_time or stop_time to start a new session

Energy Stop Time

energy_stop_time (date-time): E.g A session is started via a POST /sessions API call with a 2022-02-07T18:00:00.000Z energy stop time.
Although the session may have started earlier, and the EV may already be receiving energy, the charge station shuts off the energy flow to the EV at UTC time = 18:00.

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Use Case: Session with Energy Start and Stop Time

In many parts of the world, electricity costs vary by time of day (e.g. nighttime charging is 15% cheaper than daytime charging). The application may choose to offer nighttime (12:00Am - 06:00Am) charging to drivers as a means of saving money. With Energy Start and Stop Time the driver experience look like:

The driver returns home at 6pm, plugs in and starts a charging session. Although the session starts at 6Pm, the energy flows to the EV only between (12:00Am - 06:00Am).