Stop 04 of 09 · The three flows

Why doesn't electricity flow immediately?

About 7 min · 4 questions · Energy ·

Tuesday
The situation

Authorisation approved. The display does not jump to full power. For a few seconds it shows Preparing…, then the power climbs: 40 kW, 120 kW, 240 kW.

Twenty minutes later it falls again, although nobody touched anything.

The questionWhat happens in those first seconds, and who decides how much power flows at each moment?

Guess firstWho sets the power level at any given second?RevealHide

Not the charger, and not the driver. The car's battery management system requests what the cells can safely take at that moment, depending on their temperature and state of charge. The charger offers what it and the grid connection can deliver. The lower of the two applies, every second of the session.

The physical pathFrom the grid to the cells
01
Step 01 · PhysicalGrid

The site's grid connection was planned when the site was built. Cars charging at the same time share it, which is what load management is for.

Select each step of the energy path.

Most public charge points are ACEurope · share of charge points
AC · up to 22 kW60%
DC · 23 to 149 kW21%
HPC · 150 to 299 kW10%
HPC · 300 kW and more9%

Most public charge points in Europe are AC chargers up to 22 kW, where the car's onboard charger converts the energy, about three in five stand at sites with AC only. About one in five belongs to a site with 150 kW or more. Classified by the highest rated power of each site.

What fills those seconds

Three steps run during Preparing. Only after all three does current flow.

  • Safety check. Connector lock, then the charger checks the insulation of the high-voltage system.
  • Negotiation. Car and charger exchange their voltage and current limits.
  • Precharge. The charger matches its output voltage to the battery before the close.

The industry association CharIN describes this order for the Combined Charging System: connector lock, isolation check, precharge, then charging.

Charging curvePower follows the battery, not the charger label
PhasePlateau
Approx. power230 kW

The cells can still accept almost everything the charger can provide.

An illustrative curve for one fast-charging car. The falling number at high state of charge is the battery protecting itself, not a broken charger.

Why the power falls around minute 20

A battery fills like a stadium: quickly while the rows are empty, more slowly once seats run out. As a rule of thumb, the lower the , the higher the possible power, and the range from 10 to 80% is the one that counts for fast-charging performance. Above about 80%, charging takes disproportionately long, so on a journey it pays to unplug there. The battery also needs the right temperature for high power, which is why newer cars precondition it before a fast-charging stop.

At any moment, three limits decide the power: the grid connection of the site, the converter of the station and the battery of the car. The smallest one applies.

Check your understanding

4 questions. Answer all of them to complete this stop. Each answer explains itself.

01Question 1 of 4

What happens during the “Preparing…” seconds?

02Question 2 of 4

Charging power falls from about 240 to about 110 kW by 80% state of charge. This is…

03Question 3 of 4

Why does the same car charge in 20 minutes on the motorway but in 8 hours at home?

04Question 4 of 4

A site has four 300 kW chargers but a grid connection for 600 kW in total. Four cars arrive. What must happen?

Further in other paths

  1. Load management · Stop 01Why can't every car charge at full power?Twenty charge points of 11 kW, but only 80 kW for charging: why connections are smaller than the sum of the chargers, and why that rarely matters.
  2. Charging hardware · Stop 01Why are there AC and DC chargers?Batteries store direct current, the grid delivers alternating current. AC and DC chargers differ in one thing above all: where the current is converted.
  1. ÖAMTC: Ladetechnologie und Reichweite beim E-Auto: AC and DC charging, where the current is converted. https://www.oeamtc.at/thema/elektromobilitaet/ladetechnologie-und-reichweite-beim-e-auto-35655200. Checked 13 Oct 2026.
  2. emobility.directory: Charge point operators in Europe, from national registries of 8 countries and OpenChargeMap; Switzerland, Greece, Luxembourg and Poland left out, data as of 28 Sep 2026. https://emobility.directory/. Checked 28 Sep 2026. Charging data: Bundesnetzagentur.de (CC BY 4.0); IRVE, transport.data.gouv.fr (Licence Ouverte 2.0); NDW (CC0); DGT (CC BY); Fintraffic / digitraffic.fi (CC BY 4.0); Via Lietuva (CC BY 4.0); NOBIL by Enova (CC BY 4.0); Open Charge Map contributors (CC BY 4.0), including public sector information licensed under the Open Government Licence v2.0; combined and calculated by emobility.directory.
  3. CharIN e. V.: Design Guide for Combined Charging System, version 7: charging sequence with connector lock, isolation check and precharge. https://www.charin.global/media/pages/home/technical-details-ccs-basic/8573eac41b-1645622501/design_guide_combined_charging_system_v7.pdf. Checked 13 Oct 2026.
  4. ADAC: Noch schneller Schnellladen: charging curves, the range from 10 to 80% and battery temperature, press release, 7 August 2025. https://presse.adac.de/meldungen/adac-ev/technik/noch-schneller-schnellladen.html. Checked 13 Oct 2026.
  5. ADAC: Deutliche Unterschiede beim Schnellladen von E-Autos: fast charging on the road only to about 80%, press release, 19 February 2020. https://presse.adac.de/meldungen/adac-ev/technik/deutliche-unterschiede-beim-schnellladen-von-e-autos.html. Checked 13 Oct 2026.
  6. ADAC: Noch schneller Schnellladen: charging curves, the range from 10 to 80% and battery temperature, press release, 7 August 2025. https://presse.adac.de/meldungen/adac-ev/technik/noch-schneller-schnellladen.html. Checked 13 Oct 2026.
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