EV DC Fast-Charge Time (CC-CV Taper)
Why '80% in 20 minutes' is only the first leg.
Example
You enter
- Usable capacity (kWh) 60
- Start state of charge (%) 10
- Target state of charge (%) 100
- Charger rated power (kW) 150
- Vehicle peak DC acceptance (kW) 100
You get
- Constant-current power 100
- Fast leg (time to 80%) 25.2 min
- Total time 0.78
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeDC fast charging holds constant power (the lesser of charger and vehicle acceptance) only to about 80%, then the battery tapers to protect the cells -- modeled as three bands (0-80% full power, 80-90% ~50%, 90-100% ~25%). A 60 kWh EV from 10-100% on a 150 kW charger (100 kW acceptance) does the 10-80% fast leg in 25.2 min, then the last 20% costs another 21.6 min -- essentially the same again -- for 46.8 min total. Dividing 54 kWh by 100 kW gives 32.4 min, 14 min short, because it charges the top at power the pack never accepts. This is why fast-charge etiquette is to unplug at 80%. A planning estimate; the vehicle's charging curve governs.
Formula or tablecc_power = min(charger, acceptance); bands 0-80% at 1.0, 80-90% at 0.5, 90-100% at 0.25 x cc_power; per-band time = (capacity x band_span/100) / (cc_power x fraction); total = sum over covered bands.
Source and editionDC fast-charge CC-CV taper model (three constant-power bands), first-principles; the vehicle's charging curve governs the actual profile.
Free accessTime = energy / power per band is first-principles; the taper above 80% is inherent to lithium-ion CC-CV charging and the band powers come from the vehicle's BMS behavior.
What governsEstimate. AHJ and licensed professional govern.
API field namesusable_capacity_kwh, start_soc_pct, target_soc_pct, charger_power_kw, acceptance_kw, cc_power_kw, time_to_80_hr, time_total_hr
- Constant-current power cc_power = min(charger rating, vehicle peak DC acceptance); the pack limit usually governsDC fast charging
- Taper bands 0-80% at full power, 80-90% at ~50%, 90-100% at ~25%lithium-ion CC-CV charge curve
- Approximation breakpoints and fractions approximate a smooth manufacturer curve; chemistry and temperature shift itscope of this tile