Heat generation during fast charging
I²R losses, entropic heat and why the curve tapers.
You'll learn
- Explain heat generation during fast charging at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real pack
Overview
Rapid charging is a thermal problem disguised as an electrical one. Every kilowatt of loss becomes heat inside a sealed box.
In depth
Charging simulator
Change chemistry, power and starting temperature and watch heat build.
Chemistry
Pack capacity75 kWh
Charger power150 kW
Ambient temperature20 °C
State of charge20 %
Driving / auxiliary load0 kW
Power accepted
150.0kW
Pack voltage
368V
Current
408A
Pack temperature
29.2°C
Efficiency
94.7%
Heat generated
8.32kW
Charging curve150 kW peak
0%50%100%
Time to 80%
18 min
Formula
P_loss = I² × R_internal
Loss rises with the square of current, so the last few percent of charging power costs disproportionate heat.
Example: 300 A through 15 mΩ generates 1.35 kW of heat inside the pack.
Charge 10–60% on road trips
The power curve is highest and the heat lowest in the lower half of the pack. Two short stops usually beat one long one.
Key takeaways
Remember this
- Losses scale with the square of current.
- Taper protects the cells from heat and plating.
- Lower-SOC charging is faster and cooler.
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