How does a backend tell a charger how much power to use?
The controller recalculates for fourteen cars: ten on three phases, four on a single phase, and all four of those on L1. Every car gets the same current, and L1 may carry 116 A.
Within seconds, every charge point receives its new limit, and the cars' onboard chargers follow.
The questionHow does a limit travel from the controller to the car?
A meter at the connection reports the building's current load.
Select each step to see what happens.
116 A on L1 shared by fourteen cars
8.3 A on three phases, ten cars
8.3 A on L1 only, four cars
L1 at 116 A, L2 and L3 at 83 A
A composed example, computed with 230 V per phase. L1 carries all fourteen cars and reaches its limit first, so the total stays below 80 kW while L2 and L3 have room. Why all four single-phase cars sit on L1 is the subject of stop 05.
Profiles at three levels
has carried since version 1.6 of 2015. In OCPP 2.0.1 it is a functional block of its own: functionality that lets the operator, or indirectly a third party, influence the current or power of a session, or limit what a charging station offers. The charge point passes a limit to the car through the control pilot of the cable: high duty cycles of its signal set the maximum current. Limits can be set:
- for the whole station, as a ceiling for everything behind it,
- as a default for every new session,
- for one session, for example to follow a schedule until the car leaves.
When the connection drops
A charger that loses its backend can no longer receive new limits; it then works with the profiles it already holds. That is why sites keep a safe default in every charger: a limit that applies to new sessions whenever nothing else is known. that runs on site, in a local controller, keeps working even when the internet does not.
Since 13 April 2024, new public charge points in the EU must be capable of smart recharging.
The car can talk too
With , the car can report its energy need and planned departure time, so the backend can build an accurate profile for the session. OCPP 2.0.1 supports this exchange in full. More on that conversation in Plug & Charge.
Check your understanding
3 questions. Answer all of them to complete this stop. Each answer explains itself.
How does a charge point tell the car how much current it may draw?
The charging cable carries a control signal that sets the maximum current for the onboard charger.
Since which version has OCPP supported smart charging?
OCPP 1.6 introduced smart charging; 2.0.1 made it a functional block of its own.
Why do chargers keep a default limit for new sessions?
Without a backend, no new profiles arrive. A safe default keeps the site below its limit.
- OCPP Open Charge Point Protocol: the open protocol between a charger and its operator's backend. EV charging fundamentals, stop 03 Glossary
- Load management Shares a site's grid connection between the cars charging at the same time. EV charging fundamentals, stop 04 Glossary
- ISO 15118 International standard for the digital communication between car and charger, the basis of Plug & Charge. EV charging fundamentals, stop 08 Glossary
- Smart charging Charging whose power is adjusted in real time, based on information received electronically, for example from the grid operator or a price signal; EU law calls it smart recharging. Bidirectional charging, stop 01 Glossary
- IEC: IEC 60038:2009, IEC standard voltages, foreword: the 230/400 V system (free preview by VDE Verlag). https://www.vde-verlag.de/iec-normen/preview-pdf/info_iec60038%7Bed7.0%7Db.pdf. Checked 13 Oct 2026.
- Open Charge Alliance: What is new in OCPP 2.0.1? Whitepaper, version 1.0, March 2023. https://openchargealliance.org/wp-content/uploads/2024/01/new_in_ocpp_201-v10.pdf. Checked 09 Oct 2026. Licence: CC BY-ND 4.0.
- Open Charge Alliance: What is new in OCPP 2.0.1? Whitepaper, version 1.0, March 2023. https://openchargealliance.org/wp-content/uploads/2024/01/new_in_ocpp_201-v10.pdf. Checked 09 Oct 2026. Licence: CC BY-ND 4.0.
- CharIN e. V.: Design Guide for Combined Charging System, version 7: pulse width modulation on the control pilot, high duty cycles set the maximum current. https://www.charin.global/media/pages/home/technical-details-ccs-basic/8573eac41b-1645622501/design_guide_combined_charging_system_v7.pdf. Checked 13 Oct 2026.
- Open Charge Alliance: OCPP 1.6 edition 2 (2017), section 3.13.4 Smart Charging Use Cases (load balancing, local smart charging) and section 3.13.6 on smart charging when a charge point goes offline; free download. https://openchargealliance.org/download-ocpp/. Checked 13 Oct 2026.
- EUR-Lex: Regulation (EU) 2023/1804 (AFIR), Article 5(8). https://eur-lex.europa.eu/eli/reg/2023/1804/oj. Checked 09 Oct 2026. © European Union, reused under Commission Decision 2011/833/EU.
- Open Charge Alliance: What is new in OCPP 2.0.1? Whitepaper, version 1.0, March 2023. https://openchargealliance.org/wp-content/uploads/2024/01/new_in_ocpp_201-v10.pdf. Checked 09 Oct 2026. Licence: CC BY-ND 4.0.