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Old 02-06-09, 03:33 PM
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Originally Posted by safe View Post
Hmmmmm... no responses...
Regeneration does not need to be implemented as a drag brake. There are ebikes out there that sense brake lever position and activate regeneration when the lever is first activated, but before the brake itself is engaged. I recall reading about one system with multiple level of regeneration operated this way.

There is very little downside to this type of regeneration when applied to a direct drive hub motor, but the benefit is limited by the efficiency of the motor (likely to be about 50% during acceleration and braking, for a net result of 25% energy return) and the charging current limit on the battery. Real world energy recovery is likey to be limited to single digit percentages (ignoring the use of cutting edge technologies like ultracapacitors).

Personally, I would rather have a bike that pedals freely - without having to overcome motor cogging torque - than regenerative braking. The regeneration systems I am familiar with use direct drive hub motors that are a drag when riding without power. Geared motors (hub or otherwise) typically freewheel and cannot be used with regeneration, but they have no cogging torque and their higher efficiency should make them competitive with most regenerative systems.

From the technical standpoint the equations that apply to the motor in the forward direction are the same equations that apply in the reverse direction. A motor can either work as a motor or a generator depending on whether the current flows in or out. (in other words within a simulation it's pretty easy to see what takes place)
Because there are losses, the equations are not generally reversable. Operating as a motor, you have E_mechanical = E_electrical * efficiency, but as a generator the equation becomes E_mechanical = E_electrical/efficiency. If you want a more technically oriented discussion, check out the forums at endless sphere.
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