Dave Plowman (News) wrote:

A little bit of easily obtainable research will show that even a modest
town car will approach or even exceed 1G when braking from 30 mph if
required to do so, but even the most powerful can't approach this in
acceleration. So to provide motor/generators for each wheel which could
provide this sort of retardation would be neither practical or cost
effective.

Not only that, even if you have a 30kW motor, and you can arrange to
capture all the regen energy from breaking at maximum motor speed (i.e.
unlikely), how long will it take to come to rest at max braking? Under 5
secs that is for sure. How much extra charge can you get in your battery
- 0.8Ah best case!

Most of the energy you have put into accelerating you big pile of
batteries has been lost to heat and air resistance (proportional to the
third power of the velocity!). So even capturing all the available enegy
from the regenerative breaking you will get back a small fraction of
what you put in.

On top of which 30kW of breaking (the best you could hope for from the
motor) is useless for anything other than gentle breaking. For real
world useful breaking you will need to use the discs, and hence end up
loosing most of your kinetic energy as heat.


--
Cheers,

John.

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