Derating means a charger deliberately lowers its own charging current because it is getting too warm. It is a built-in protection, not a fault: the charger senses rising internal temperature and trades speed for safety until things cool down. When the temperature falls, full current normally returns on its own.
Key Takeaways
- Derating is a charger’s built-in heat protection: it cuts current, then restores it when cool.
- It is not the same as battery taper near full, and not the same as a fault.
- Shade, airflow and a lower current setting on hot days prevent most derating.
- Slowdowns in mild weather, fault lights or a hot plug need professional attention.
What Derating Actually Is
Every charger converts and switches power, and that work produces heat inside the enclosure. Electronics are rated for a set operating temperature range, which you will find in the manual. If the inside of the unit approaches the top of that range, the controller reduces the current in steps. Less current means less heat, so the charger protects itself instead of shutting down completely or being damaged. A session that starts at full speed and quietly slows on a hot afternoon is usually derating at work. It is different from your car asking for less power: here, the limit comes from the charger’s own temperature sensors.
Derating, Taper or a Fault?
Three different things can make charging slow down, and they are easy to tell apart once you know the signs.
| What you see | Likely cause | What happens next |
|---|---|---|
| Speed drops as the battery passes roughly 80% | Normal battery taper, controlled by the car | Nothing to fix; see why charging slows after 80% |
| Speed drops on hot days, recovers overnight or in cooler weather | Charger derating to control its own heat | Usually self-corrects when the unit cools |
| Charging stops, a fault light shows, or the breaker trips | A fault or protection trip, not derating | Stop and investigate; persistent faults need an electrician or the manufacturer |
What Triggers Derating
- Hot surroundings. A wallbox in direct sun or a garage that bakes in the afternoon starts closer to its limit. Our guide to charging in hot climates covers siting in detail.
- High current for hours. Home charging is a continuous load, so a long session at maximum current builds heat steadily.
- Portable units in bad spots. A portable charger left on hot asphalt, in a closed car, or under a cover has nowhere to shed heat.
- Blocked airflow. Chargers stored in tight cabinets or buried under garage clutter run hotter than the same unit with space around it.
What to Do When Your Charger Derates
Start with the environment: shade the unit if you can, clear space around it, and avoid running a portable charger in direct sun. If your charger or car offers a lower current setting, using it on very hot days often holds a steadier speed than starting at maximum and being derated. Scheduling the bulk of a session for the cooler evening hours also helps. If speeds fall even in mild weather, or the unit feels excessively hot, smells, or shows damage, stop using it and contact the manufacturer or a licensed electrician. Heat in the cable and plug is a related topic — see whether EV charging cables should get hot, and our diagnosis guide if your car is charging slowly at home for other reasons.
Chargers Built for Warm, Long Sessions
Current you can set yourself is the simplest defence against heat slowdowns. The EV-ACS3210T portable charger offers 10–32 A in six steps, so you can pick a cooler setting on hot days, and it is rated IP66 for outdoor use. For a fixed installation, the EV-ACT5006T wall charger delivers up to 48 A hard-wired or via a NEMA 14-50 plug, with an IP65/IP66 enclosure for indoor or outdoor mounting.
Frequently Asked Questions
Is derating dangerous?
No. Derating is the safety system working as designed. The charger slows down precisely so temperatures stay inside its rated range. Worry instead about a charger that stops completely, shows a fault, or has a hot plug or damaged cable.
Does derating harm the battery?
No. The car simply receives less current for a while, much like charging with a smaller charger. The session takes longer, but slower charging is not harmful to the battery.
Why does my neighbour’s identical charger not slow down?
Placement is usually the difference: shade, airflow, ambient temperature and the current setting all change how much heat builds up. Two identical units in different spots can behave differently on the same day.
Related Reading
- Hot-Climate EV Charging: Protecting Chargers From Desert Heat and Sun
- Why Is My Electric Car Charging Slowly at Home?
- Do EV Charging Cables Get Hot?
- Why Does EV Charging Slow Down After 80%?
