What is EV charger derating?
Charger derating means reducing the power available below the equipment's nominal rating, for example because of temperature limits [S3]. Low delivered power can also reflect the vehicle or site controls. Energy Saving Trust notes rapid charging can slow above 80% battery charge [S1]. Ask your operator to identify the limiting factor before changing equipment. Checked October 2026.
What is charger derating?
Charger derating is a reduction in the power available below the equipment’s nominal rating, including reductions linked to temperature conditions [S3].
Why it matters for your site: the advertised maximum may not describe the power a visitor receives throughout a session. Separate equipment derating from vehicle limits and deliberate site power allocation.
Kilowatts (kW) measure power; kilowatt-hours (kWh) measure energy delivered over time. Read charging speeds explained before interpreting a session record.
Why does delivered charging power fall?
Check the cause rather than treating every low reading as the same fault.
| Possible limit | Evidence to request |
|---|---|
| Equipment heat | Temperature record, alarms and the model’s derating curve |
| Shared power | Other active outlets and allocation settings |
| Vehicle | Battery charge, temperature and charging capability |
| Site supply | Building demand and configured charging limit |
Archived charger-module datasheets hosted by CHAdeMO specify temperature-related output reductions [S3]. They illustrate the mechanism; their thresholds are not specifications for your equipment.
Energy Saving Trust describes load management distributing available power between vehicles [S2]. It also notes that rapid charging can slow above 80% battery charge [S1], while cold batteries can accept charge more slowly [S4]. These are different explanations for a reduced reading.
How can you estimate the effect on charging time?
Illustration, not a quote: assume a vehicle needs 20 kWh and accepts constant power, ignoring losses and tapering. At an assumed 50 kW, time = 20 ÷ 50 = 0.4 hours. At an assumed 25 kW, time = 20 ÷ 25 = 0.8 hours.
That arithmetic shows why sustained output matters. Request measured session records before promising visitors a charging duration. Read power sharing and use the charging cost tool for separate price assumptions.
For building-demand controls, read dynamic load management.
Next step
Browse the glossary for related definitions.
Use the site check and customer and staff hub, then get matched with an installer that covers your area.
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Common questions
Does slower charging always mean the charger is faulty?
No. Energy Saving Trust describes power allocation through load management and reduced rapid-charging speed at higher battery charge [S1], [S2]. Check those conditions alongside equipment alarms.
Can a cold battery reduce charging power?
Yes. Energy Saving Trust explains that a cold battery accepts charge more slowly [S4]. Ask the driver about battery preparation and record the conditions before diagnosing the charger.
Do two outlets each receive the full cabinet rating?
Do not assume so. Load management can distribute available power among connected vehicles [S2]. Request total and per-outlet limits for simultaneous sessions.
Does the same temperature threshold apply to every charger?
No common threshold is established here. The archived datasheets show limits for particular modules [S3]. Ask for the output-versus-temperature specification for your exact equipment.
Can building demand reduce charging power?
Yes. Dynamic load management monitors site use and allocates available capacity to charging [S2]. Ask whether the reduction matches the configured limit and operating schedule.
Ask about your site
Sources
- Charging electric vehicles, Energy Saving Trust,Last checked 19 October 2026
- Charging profiles and site load management, Energy Saving Trust,Last checked 19 October 2026
- Archived V2G charger module datasheets, temperature and output limits, CHAdeMO Association (document host),Last checked 19 October 2026
- Battery electric vehicles, seasonal charging effects, Energy Saving Trust,Last checked 19 October 2026