Re: Regenerative Braking?


daestrom wrote:
"BobG" <bobgardner@xxxxxxx> wrote in message
news:1141842105.410326.270820@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
This sounds like snake oil. Lets say the battery bank is 48V. We're
driving along at 40mph, maybe humping 35V into the motor.... now take
foot off the gas... motor is outputting about 30V lets say.... to get
this back into the battery, you need to hump it up above 48V right? And
to load down the motor to apply braking, you would need a low impedance
load to hook across the motor that would absorb that 30V.... maybe a
bank of boostcaps, but then you need a separate dc to dc converter to
get it out of the boostcap bank and back into the batteries?


There are several ways to boost the output voltage of the motor/generator
while braking so that the energy can be reclaimed. The obvious one is to
increase the magnetic field strength. That method has been used with
regenerative braking systems in stationary machinery for many years.

You seem to have *assumed* a particular type of motor (permanent magnet
perhaps?).

daestrom

Agreed. I work with machinery that provides regenerative braking down
to a full stop. Friction brakes are provided for added safety and to
prevent motion when already stopped. These drives have an efficiency
of about 95%. Most of the current hybrid cars use small motors that
cannot slow the car as quickly as you often need to. Consider the
distance covered to accelerate a 3000 lb car from 0 to 60 mph with a 20
hp motor. Using that same motor as a generator will require the same
distance to stop the car. BTW a 40 hp car weighing about 2000 lbs
accelerates to about 60 mpy in a quarter mile.

.

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