My mobility scooter has a motor controller with regenerative braking - but regeneration seems to take place even at low speeds, well under the maximum! I know it does this because if I reduce throttle at low speed going down a hill, I see the current reverse on the ammeter and the battery voltage start to climb - considerably higher than with no load.
How does the controller achieve this? Normally, charging can only take place when the motor's generated voltage exceeds that of the battery - and this cannot happen at low speed. I ask because I want to build one from scratch.