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A moving vehicle stores kinetic energy KE = ½mv². In a conventional car, braking turns all of it into wasted heat in the brake pads. An electric or hybrid vehicle instead runs its motor as a generator during braking, converting some of that kinetic energy back into electricity to recharge the battery. The recoverable amount is the change in kinetic energy between the two speeds, multiplied by the round-trip regen efficiency (motor + inverter + battery losses).
| Quantity | Formula |
|---|---|
| Kinetic energy | KE = ½·m·v² (v in m/s) |
| Energy to shed | ΔKE = ½·m·(v1² − v2²) |
| Recovered energy | E = ΔKE × ηregen |
| In watt-hours | Wh = Joules / 3600 |
Real regen efficiency is typically 60–70%: not all braking can be regenerative (hard stops still need friction brakes), and the motor, inverter and battery each lose a little. Speeds must be converted from km/h to m/s (divide by 3.6) before squaring, since energy uses SI units.
The kinetic energy of a moving vehicle is ½mv2, and because it depends on the square of speed, the recoverable amount changes dramatically with how fast you were going.
A 1,500 kg car at 100 km/h (27.78 m/s) carries ½ × 1500 × 27.782 ≈ 578.7 kJ, which is about 0.161 kWh. The same car at 50 km/h carries only 0.040 kWh — a quarter as much, from half the speed.
Not all of that reaches the battery. The energy passes through the motor acting as a generator, the inverter, and then the cell's own internal resistance, with each stage taking a cut. Typical end-to-end recovery is 60–80%, so the 100 km/h stop above returns roughly 0.11 kWh at 70%. And that energy has to come back out of the pack later, through the same losses in reverse, so the true round-trip benefit is smaller again.
Regenerative braking can only recover energy you are throwing away by slowing down. Urban driving is a near-continuous cycle of acceleration and deceleration, so a large fraction of the traction energy passes through regen repeatedly — which is why electric cars post better city figures than highway ones. Steady motorway cruising involves almost no braking; the energy is going into air drag, which nothing can recover.
It is a braking method where the electric motor acts as a generator, converting the vehicle's kinetic energy back into electricity to recharge the battery instead of wasting it as heat in friction brakes.
Typically 60–70% of the kinetic energy shed during braking, because the motor, inverter and battery each lose some energy and hard stops still need friction brakes for safety.
Use KE = ½·m·v², with mass in kilograms and speed in metres per second. Convert km/h to m/s by dividing by 3.6 before squaring.
For a 1600 kg car, the kinetic energy is about 617 kJ (0.17 kWh). At 60% regen efficiency roughly 0.10 kWh returns to the battery.
Kinetic energy grows with the square of speed, so braking from a high speed stores — and can recover — far more energy. Braking from 100 km/h has four times the energy of braking from 50 km/h.
It is most effective at higher speeds. At very low speeds the recoverable power drops and friction brakes take over, so the last few km/h usually recover little energy.
Losses in the motor windings, the inverter, and charging the battery, plus the fact that not all deceleration can be regenerative. Battery state of charge also matters — a full battery cannot accept regen.
No. If the battery is at or near 100% state of charge it cannot absorb more energy, so the car limits regen and relies on friction braking. This is why regen feels weaker with a full battery.
In stop-start city driving regen can recover a meaningful share of energy, often extending range by 10–25% compared with no regen. On steady highway driving the benefit is small because there is little braking.
Yes. Kinetic energy is proportional to mass, so heavy vehicles like buses and trucks store and recover much more energy per stop, making regen especially valuable for them.
A mode where lifting off the accelerator applies strong regenerative braking, often bringing the car to a stop without touching the brake pedal, maximising energy recovery in city traffic.
Yes. Because the motor does most of the slowing, the friction brakes are used far less, so EV brake pads and discs often last much longer than in conventional cars.
Start from kinetic energy, E = ½mv², with mass in kilograms and speed in metres per second, then multiply by the recovery efficiency. Divide joules by 3,600,000 to get kilowatt-hours.
A 1,500 kg vehicle carries about 578.7 kJ, or roughly 0.161 kWh. At 70% recovery efficiency about 0.113 kWh returns to the battery.
Because kinetic energy depends on the square of velocity. Half the speed gives one quarter of the energy, which is why high-speed stops are where regeneration contributes most.
End-to-end recovery is typically 60–80% once motor, inverter and battery losses are included. The useful round-trip figure is lower still, since the stored energy loses more on the way back out.
A fully charged pack cannot safely accept more current, so the control system reduces or disables regeneration and shifts braking to the friction brakes. The same happens when cells are very cold.
No. It handles light and moderate deceleration, but hard stops exceed what the motor and inverter can absorb, and the vehicle still needs friction brakes for emergency stops and for holding the car stationary.
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