Power derating is the intentional or automatic reduction of a charger’s maximum output power below its rated level to protect equipment and maintain safe, reliable operation. Derating is typically triggered by conditions such as high temperature, limited cooling capacity, component protection thresholds, or electrical constraints.
In EV charging, derating can apply to AC chargers, DC fast chargers, cables, connectors, or entire sites.
Why Power Derating Matters in EV Charging
Derating protects hardware and helps prevent faults, downtime, and safety risks. It matters because it can:
– Prevent overheating of power electronics, cables, and connectors
– Avoid damage to components and extend equipment lifetime
– Maintain charging continuity instead of shutting down completely
– Affect user experience and site throughput (sessions take longer)
– Influence site planning in hot climates or high-utilization depots
Common Causes of Power Derating
Power derating is typically caused by one or more of the following:
– High ambient temperature or direct sun exposure
– Internal temperature limits reached (power modules, heatsinks, capacitors)
– Cooling system limits (fan failure, blocked airflow, low coolant flow)
– Connector or cable overheating (high contact resistance, worn pins)
– Input voltage limits or unstable grid conditions (undervoltage events)
– Site-level constraints via load management (operational derating)
– Long-duration high-load operation leading to thermal saturation
How Power Derating Works
Derating can be implemented in several ways:
– Step derating: power drops to predefined levels when thresholds are crossed
– Linear derating: power gradually reduces as temperature rises above a set point
– Dynamic derating: real-time adjustment based on thermal models and sensor feedback
– Cable/connector derating: output is limited to protect the connector temperature sensor or cable rating
If conditions worsen, derating may progress to a full stop to prevent damage.
Where Derating Is Seen Most Often
– DC fast chargers in hot weather or direct sunlight
– High-utilization hubs with continuous high-power sessions
– Fleet depots with sustained overnight charging in enclosed areas
– Sites with restricted ventilation or dirty filters/blocked airflow paths
– Installations using long or heavily loaded cables and connectors
How Operators Reduce Unwanted Derating
Common mitigation measures include:
– Improve airflow and ventilation (cabinet placement, clearances, filter maintenance)
– Add shading/canopies and avoid direct sun on cabinets where possible
– Maintain fans, pumps, and coolant systems proactively
– Use appropriate liquid-cooled cables for higher continuous DC currents
– Monitor connector wear and replace high-resistance plugs early
– Use peak shaving and load management to avoid sustained thermal saturation
Benefits (When Managed Correctly)
– Protects equipment and increases lifetime
– Maintains service continuity instead of sudden shutdowns
– Reduces fire and safety risks from overheating
– Helps meet reliability targets under variable site conditions
Limitations and Practical Considerations
– Reduces charging speed, increasing dwell time and potentially causing queues
– Can reduce revenue and user satisfaction if frequent or unpredictable
– Needs clear monitoring and fault codes so derating isn’t mistaken for “slow chargers”
– Should be considered in site performance guarantees and SLA planning
– Thermal conditions vary by installation; identical chargers can derate differently depending on placement and environment
Related Glossary Terms
Thermal Management
Heat Stress Derating
Liquid Cooling
Liquid-Cooled Cables
Power Modules
IGBT Modules
Power Curtailment
Peak Shaving
Power Quality
Charger Utilization