Why you never get 100% back
Every stage of the recovery chain loses a slice of energy to resistance, switching and friction.
- Explain why you never get 100% back at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real braking system
Overview
Kinetic energy passes through the driveline, the motor, the inverter and the battery on its way to being stored, and each stage is imperfect. Understanding the loss chain explains why real-world recovery efficiency sits around 60–70%, not 100%.
In depth
Where the biggest losses hide
Motor and inverter losses scale with the square of current, so hard, high-current regen stops are proportionally less efficient than gentle ones. Battery charge acceptance losses come from internal resistance heating the cells, which is why a cold or nearly-full pack recovers energy less efficiently than a warm, partially depleted one.
| Gentle lift-off | Moderate braking | Hard braking | |
|---|---|---|---|
| Typical current | Low | Medium | High |
| I²R losses | Small | Moderate | Large |
| Net recovery efficiency | 70–75% | 60–68% | 45–55% |
Recovery efficiency check
- 1
Why is hard regen braking less efficient than gentle regen?
- 2
Real-world regen recovery is typically close to 100% of kinetic energy.
Key takeaways
- Every stage from wheel to cell loses some energy, typically netting 60–70% recovery.
- Losses scale with the square of current, so hard braking is less efficient per joule than gentle braking.
- Cold or near-full batteries accept regen charge less efficiently.
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