BMS

Battery management system: the car's electronics that decide how much power the battery accepts at each moment.

Explained in

EV charging fundamentals · Stop 04Why doesn't electricity flow immediately?Authorisation is approved, yet the display shows Preparing and power later falls on its own. Safety checks, the handshake and the charging curve explained.

A battery fills like a stadium: quickly while the rows are empty, more slowly once seats run out. As the battery fills, the battery management system lowers the power to protect the cells, most steeply above roughly 80%, so the last 20% take disproportionately long. That is why car manufacturers state fast-charging times from 10 to 80%.

From “Why the power falls around minute 20”, stop 04

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  1. Load managementShares a site's grid connection between the cars charging at the same time.
  2. ContactorAn electrically operated switch for high currents; in a DC charger it connects the output to the car only after both have checked the connection and matched the voltage.