On 20 Nov 2007 14:03:46 GMT, James Robinson wrote in
:

Larry Dighera wrote:

Orval Fairbairn wrote:

Regenerative braking is a fantasy! Batteries are not set up to take
high-wattage charging, which is what regenerative braking really is.
In addition, the assumption of RB is that braking is a slow process;
in reality, it is a rather fast process, where the energy of motion
is converted to heat, through the brakes.

You are correct to suspect the physics of regenerative braking, but
that doesn't mean it can't be done. The electricity generated by the
motor when the brakes are applied is stored in a low impedance
capacitor. There's some information about the technique used on an
electrically powered vehicle that has no brakes he

http://www.gizmag.com/go/6104/1/
Another of the tricks employed by PML is the use of a 350V, 11
Farad ultracapacitor. Capacitors are used to store electrical
energy and can release/absorb their energy 10 times faster than a
battery. Using an ultracapacitor means that acceleration or power
boost at higher speeds can get energy twice as fast at peak draw,
offering “nitro-like performance.”

Let's see. An fully-charged 11 farad capacitor at 350 volts can provide
about 15 horsepower for 10 seconds. Not exactly a huge amount of power
storage, but it is something.

I would be better persuaded by your assertion if you provided the
calculations you used to arrive at your conclusion or an objective,
credible source that supports it.

The capacitor would also weigh about 75 lb., so you would have to take
into account the energy cost of accelerating and hauling the extra weight
as a discount against the saving from recovering braking energy.

See above.

A quick calculation suggests that the extra weight hauled for 10 miles
would consume the same amount of energy as one charge cycle of the
capacitor. Accelerating that weight would use about 10% of the useful
charge of the capacitor. Thus, the capacitor has to be fully charged at
least every 9 miles, on average, to simply break even. That might give
some benefit in city driving, but would likely be a cost on a highway.

See above.

Yes, energy recovery from regenerative braking is a reality, but it is
more hype than anything else.

See above.

In the first place, you only get energy recovery when the brakes are
applied. With highway driving, braking is not that common, so the amount
of energy recovered is vanishingly small, and there might be a cost in
hauling the extra weight of the storage medium around.

In my experience, the freeway congestion within 100 miles of Los
Angeles provides ample opportunity for braking.

Second, even when the brakes are applied, you have a couple of issues:
The amount of energy recovered will only be a fraction of the energy
available from braking because of the losses in the charge/discharge
cycle.

What would you expect the efficiency of the Supercapacitor
charge/discharge cycle to be?

http://en.wikipedia.org/wiki/Ultracapacitor
Other advantages of supercapacitors compared with rechargeable
batteries are extremely low internal resistance or ESR, high
efficiency (up to 97-98%), high output power, extremely low
heating levels, and improved safety. According to ITS (Institute
of Transportation Studies, Davis, CA) test results, the specific
power of supercapacitors can exceed 6 kW/kg at 95% efficiency

With batteries, it might be less than 50 percent given the
efficiency losses at high charge rates.

Please provide the data upon which your conclusion above is based.

There is also an economic consideration. The motor and control system
has to be sized to handle the peak power flow,

While that may be a consideration for the control system, I would
expect it to be a non-issue for the motor and the conductors used in
the connecting the battery and the motor, because the time durations
involved should be brief, so any heating due to the overload would not
have sufficient time to cause harm. (Hey, I can guess too.)

and in heavy braking it
might be 10 times that required for acceleration. Consider that an
energy-efficient car might do zero to 60 in say 20 seconds, but is able
to stop from 60 mph in less than two seconds.

The prototype electric Mini Cooper and Tesla Roadster mentioned in
these links seem to do 0 to 60 mph in ~4 seconds:

http://www.teslamotors.com/performan...and_torque.php
The Tesla Roadster’s specs illustrate what it does (0 to 60 mph in
under 4 seconds)...

http://www.gizmag.com/go/6104/1/
In the MINI QED, this package offers a 0-60mph time of 3.7 seconds
and a 150mph top speed ...

I'd say that five fold error casts some doubt on your other
unsubstantiated conclusions.

The designer of a vehicle knows that the cost of the motor and control
system varies in about direct proportion to the power to be handled. He
would have to determine whether it would be economically reasonable to
provide a motor that is ten times the size and cost needed for
acceleration just to capture all of the small amount of braking energy
available.

That statement reveals a fundamental misunderstanding. While it may
be true that the active semiconductors may need to be sized for the
peak current, that reasoning is inappropriate for the motor and
conductors.

For a real-world example, look at the current hybrids. They use friction
brakes at highway speeds, and do not recover braking energy
regeneratively,

Where did you get that idea?

http://www.toyota.com/prius/specs.html
Brakes Power-assisted ventilated front disc/rear drum with
Anti-lock Brake System (ABS) and integrated regenerative braking

so you can see the designers did not figure it was worth
it to capture all of the braking energy. The same principle would likely
apply to all-electric vehicles.

With all due respect, you talk as though you have all the answers, but
fail to provide a shred of hard evidence, let alone credible sources,
to support your assertions. Lacking that, I am unconvinced of your
arguments.