A brownout is a condition where the electrical grid supply voltage drops below its normal level for a period of time, without a complete loss of power. In EV charging, brownouts can cause chargers to reduce power, pause charging, or fault if voltage remains outside acceptable limits, and they can also affect site reliability and availability rate.
What Is a Brownout?
A brownout is a sustained undervoltage event. Unlike a blackout (total loss of power), during a brownout electricity is still available, but at a reduced voltage level. Brownouts may be:
– Utility-controlled (intentional voltage reduction to manage demand)
– Caused by grid congestion, equipment issues, or long feeder lines
– Triggered by local load spikes (large motors, high demand periods)
Brownouts can vary in severity and duration, from brief periods to extended events.
Why Brownouts Matter in EV Charging
EV chargers and vehicles are designed to operate within defined voltage ranges. When voltage drops too low:
– Chargers may reduce output power to stay within safe operating limits
– Sessions may terminate if protection thresholds are crossed
– Power electronics can overheat due to higher current draw for the same power
– Communication equipment and payment terminals may behave unpredictably
– Multiple chargers on the same site can become unstable under heavy load
For fleets and public charging hubs, brownouts can reduce throughput and increase failed sessions.
How EV Charging Systems Respond to Brownouts
Typical charger and site responses include:
– Power derating: the charger reduces current to maintain stable operation
– Protective shutdown: the charger stops charging if voltage falls below minimum thresholds
– Fault reporting: events recorded in logs and sent to the back-end via OCPP
– Recovery behavior: automatic restart when voltage returns to normal (site-dependent)
– Load management response: site controller may lower total charging load to stabilize voltage
Vehicles can also limit charging if they detect unstable supply conditions.
Common Causes of Brownouts at Charging Sites
– Weak grid connection or long cable runs causing voltage drop under load
– High site demand exceeding available import capacity
– Undersized transformers, switchgear, or feeders
– Poor phase balance in three-phase systems
– Utility network issues during peak demand periods
– Sudden load changes from other equipment on site
How to Reduce Brownout Impact
Typical mitigation strategies include:
– Proper electrical design to limit voltage drop (correct conductor sizing, shorter runs)
– Site-level load management and active power throttling
– Upgrading the grid connection or transformer capacity where necessary
– Using behind-the-meter storage (BESS) to support peak loads and stabilize import
– Power quality monitoring to identify patterns and root causes
– Ensuring chargers and protections are configured correctly for undervoltage events
Key Benefits of Managing Brownouts
– Higher charging reliability and fewer session failures
– Better user experience and improved site reputation
– Higher utilization and revenue stability for operators
– Reduced wear on power electronics and protection devices
– Improved compliance with uptime and SLA expectations
Limitations to Consider
– Mitigation may require utility cooperation or infrastructure upgrades
– Brownouts can be intermittent and difficult to diagnose without monitoring data
– Severe undervoltage may still force shutdown regardless of mitigation
– Some sites face structural constraints (long runs, shared infrastructure) that limit design options
Related Glossary Terms
Undervoltage
Voltage Drop
Power Quality
Availability
Availability Rate
Load Management
Active Power Throttling
Behind-the-Meter Storage
Grid Connection Permit
Blackout