Fuel Savings from Roadbed Electrification Pays for the Power

[John Fields]

On Fri, 5 Jun 2009 20:48:33 -0700 (PDT), Bret Cahill
<BretCahill@peoplepc.com> wrote:

I'm not well versed in this field, so I'm asking: If the input to a DC
motor is shorted, once it's running, why would it take longer to stop it
than to run it up using a voltage source with a higher impedance than
the brake?
---

Huh?

That what I said when he said circular furrows were impossible.

If you short any motor, AC or DC, ?it will stop faster than you can finish
the word "stop".

John Fields has an IQ of 14.

---
Considering the number of times I've skewered you, then, that puts you
at about a solid 4, yes?

JF

 

[John Fields]

On Fri, 5 Jun 2009 21:20:47 -0700 (PDT), Bret Cahill
<BretCahill@peoplepc.com> wrote:

The reality is that if fuel goes to $15 per gallon there'll be an awful
lot of us working from home.

John Fields can provide the on line entertainment by claiming circular
furrows are impossible, that adiabatic engine systems might not scale
up . . .

---
And by shooting you down with incontrovertible logic and watching you
crash and burn with no way of getting out of your plight.
---

And people who have to "be there" on the job,

If they want to get there they'll soon have to motor off the grid as
fuel costs have been increasing by 10% _a month_.

for example construction
workers (there will be construction)

We can only hope some will be working on getting energy to vehicles.

to plumbers and medics will be
making more money than egg heads.

Number crunching is so so so . . . gauche!.

---
If all you know how to do is run a spreadsheet, perhaps.

JF

 

[john joseph]

tgdenning@earthlink.net wrote:

On Jun 5, 9:35 pm, john joseph <nowh...@nowhere.nl> wrote:

I think maybe you are not reading carefully and just overreacting. I
said that electric motors can be reversed, which means that they have
as much 'stopping potential' as they have starting potential.

But they do not.

Now you are being silly. Do you understand what reversing the motor
means?

"as much stopping potential as starting potential" is incorrect. It is
not proportionate. The stopping potential depends upon the electrical
load of the system. More 'need for juice' == greater stopping power.

Using the electric motor as a brake in an automobile requires a load on
the electrical system. Granted, such is usually the case, for example
when the battery is not fully charged and an appliance or the lights are
on. Regardless, super capacitors can add to the necessary load.

But it's not proportionate. Not really.

Aside: the lights and accessories of the conventional car draw extra
horsepower than if they were off. It's related to the load on the
alternator/generator. So driving with everything on causes a minor loss
in mileage. Oh, and your alternator does not recharge the conventional
car system when you take your foot off the gas at speed because it's
engineered (using a diode) to direct the juice one-way. Removing that
diode will raise hell.

A funny and pathetic aside - At one time Volkswagen used the generator
warning light bulb (a tiny thing in the speedometer) to first energize
the alternator's field so that it would generate electricity. If that
stupid bulb burned out, then after you stopped the engine and started it
again, you just drew from the battery because the alternator was not
energized, was not charging. Lesson: if it did not come on don't just
think "aw it's just an affirmation bulb" and drive away - your battery
will discharge eventually and turn you into a pedestrian. (problem
solved with tiny resistor in circuit.)

 

[john joseph]

tgdenning@earthlink.net wrote:

On Jun 6, 9:47 am, john joseph <nowh...@nowhere.nl> wrote:
tgdenn...@earthlink.net wrote:
On Jun 5, 9:35 pm, john joseph <nowh...@nowhere.nl> wrote:
I think maybe you are not reading carefully and just overreacting. I
said that electric motors can be reversed, which means that they have
as much 'stopping potential' as they have starting potential.
But they do not.
Now you are being silly. Do you understand what reversing the motor
means?
"as much stopping potential as starting potential" is incorrect. It is
not proportionate. The stopping potential depends upon the electrical
load of the system. More 'need for juice' == greater stopping power.

Using the electric motor as a brake in an automobile requires a load on
the electrical system. Granted, such is usually the case, for example
when the battery is not fully charged and an appliance or the lights are
on. Regardless, super capacitors can add to the necessary load.

But it's not proportionate. Not really.


Ok, now I can see that you actually don't get what I am saying. By
reverse, I don't mean "reverse the function so the motor becomes a
generator". I mean "reverse the direction that the motor is trying to
turn", which will actually *use* battery juice that is already stored.

But that is not regenerative, which I presumed we were talking about; in
fact, what you propose wastes battery power in the form of heat - one of
the things we are trying to avoid with an electric or hybrid.

Remember, the original question was whether you can bring the car to a
complete stop using only electricity and no mechanical brakes. The
answer is yes.

Remember, we already settled the fact that conventional braking is still
required, so the point is academic as you point to below.

I am suggesting that there will be a combination of effects used to
provide the system load, and that over time, it will develop into a
mostly electric system which gives ABS, and mechanical brakes will be
a back-up component and for parking.

ABS today is hydraulic/mechanical with electricity only providing
control of the hydraulic valves and timing of the same. I know
electrical brakes and so far the hydraulic brake is so effective I've
never considered a fully electric alternative. I'll keep an eye out for
them.

Right now, it isn't even legal to
have a car without mechanical brakes, no matter how reliable electric
braking could be made, so the argument is purely academic.

OTOH, electric brakes are quite common in small (car sized) trailers. If
I lost power to mine, they would go into default behavior of a modest
amount of mechanical brake without controls for more or less; if they
were to fail, I'd just crank the brakes out to disable them (providing I
stopped under control).

 

On Jun 6, 9:47 am, john joseph <nowh...@nowhere.nl> wrote:

tgdenn...@earthlink.net wrote:
On Jun 5, 9:35 pm, john joseph <nowh...@nowhere.nl> wrote:
I think maybe you are not reading carefully and just overreacting. I
said that electric motors can be reversed, which means that they have
as much 'stopping potential' as they have starting potential.
But they do not.

Now you are being silly. Do you understand what reversing the motor
means?

"as much stopping potential as starting potential" is incorrect. It is
not proportionate. The stopping potential depends upon the electrical
load of the system. More 'need for juice' == greater stopping power.

Using the electric motor as a brake in an automobile requires a load on
the electrical system. Granted, such is usually the case, for example
when the battery is not fully charged and an appliance or the lights are
on. Regardless, super capacitors can add to the necessary load.

But it's not proportionate. Not really.

Ok, now I can see that you actually don't get what I am saying. By
reverse, I don't mean "reverse the function so the motor becomes a
generator". I mean "reverse the direction that the motor is trying to
turn", which will actually *use* battery juice that is already stored.

Remember, the original question was whether you can bring the car to a
complete stop using only electricity and no mechanical brakes. The
answer is yes.

You are correct that it is not a simple 1:1 relationship in a
practical sense to stop the car with the generator effect. The most
obvious reason is that you usually would like to stop faster than you
have accelerated to the current speed, and you may be going downhill
as well. This means that even if you 'short' the motor<>generator as
someone suggested, the kinetic energy of the car will be have to be
dissipated as heat at a rate that will prevent damage to the motor.

I am suggesting that there will be a combination of effects used to
provide the system load, and that over time, it will develop into a
mostly electric system which gives ABS, and mechanical brakes will be
a back-up component and for parking. Right now, it isn't even legal to
have a car without mechanical brakes, no matter how reliable electric
braking could be made, so the argument is purely academic.

-tg

Aside: the lights and accessories of the conventional car draw extra
horsepower than if they were off. It's related to the load on the
alternator/generator. So driving with everything on causes a minor loss
in mileage. Oh, and your alternator does not recharge the conventional
car system when you take your foot off the gas at speed because it's
engineered (using a diode) to direct the juice one-way. Removing that
diode will raise hell.

A funny and pathetic aside - At one time Volkswagen used the generator
warning light bulb (a tiny thing in the speedometer) to first energize
the alternator's field so that it would generate electricity. If that
stupid bulb burned out, then after you stopped the engine and started it
again, you just drew from the battery because the alternator was not
energized, was not charging. Lesson: if it did not come on don't just
think "aw it's just an affirmation bulb" and drive away - your battery
will discharge eventually and turn you into a pedestrian. (problem
solved with tiny resistor in circuit.)

 

In sci.physics Bret Cahill <BretCahill@peoplepc.com> wrote:

$10 million/mile doesn't buy much more than paving these days.

Is that $10 million per mile or mile lane?

No answer?

Here's a clue for you:

Adding one lane to the 57 Freeway for about 5 miles is estimated to cost
$140 million.

That only highlights some the cost advantages of electrification over
new highway construction:

No, it highlights the fact that road construction and maintenance is
extremely expensive these days.

It is no longer 1957.

There are a myrid of things that make todays roads expensive to build and
maintain.

<snip long winded babble that totally misses the point>

We don't need every last fuel powered vehicle off the road
immediately.

It doesn't matter what you think we need.

The reality is the median age of a car in the US is 9.4 years and
climbing.

With hybrids we can phase it in gradually thereby lessening the oil
shock.

Not unless:

A) Any changes to roads are 100% compatible with all existing vehicles.

B) All new vehicles have the same capabilities as existing vehicles.

That means "we" would have to electrify all 210,000 lane miles of
highway first, then about 10 years after that is done about half
of the cars on the road would be able to use the electricity provided.

You have yet to provide a viable scheme to achieve that.

You have yet to provide a rough cost to achieve that.

I have no interest in hearing any childish babble about spreadsheets.

The people here built a demo system without spreadsheets:

http://www.path.berkeley.edu/PATH/Publications/PDF/PRR/94/PRR-94-07.pdf

How much to put such a system on 210,000 lane miles of highway?

I assume you can come up with a pencil and an old envelope, which is
all you need to do the calculations.


--
Jim Pennino

Remove .spam.sux to reply.

 

[Bret Cahill]

$10 million/mile doesn't buy much more than paving these days.

Is that $10 million per mile or mile lane?

No answer?

Here's a clue for you:

Adding one lane to the 57 Freeway for about 5 miles is estimated to cost
$140 million.

That only highlights some the cost advantages of electrification over
new highway construction:

EVs and hybrids can charge up where ever the road bed is electrified,
that is, where ever it was cost effective to electrify, and then run
off the battery if a 5 mile stretch is prohibitively expensive to
electrify. 100% coverage isn't necessay for a motorist to be able to
fuellessly access 100% of a region. Ramps might not be cost effective
either.

This isn't true for conventional new highway construction where they
don't have the option to "merely omit" ramps and new lanes which
require condemning / buying expensive land downtown.

But we keep overlooking the real advantage of electrification:
convenience. Battery only EV travel will soon be competitive with
liquid fuel on an overall [capital + operating] _per mile_ basis when
fuel reaches something like $6 - $8 gallon.

The problem is even then electric only travel still won't be
_convenient_.

You charge up at home and if you go more than a few dozen miles your
EV is either stuck or your hybrid is right back to liquid fuel.

Everyone within 40 miles of an electrified freeway however -- about
99.99% of the population -- could charge his Volt at home, drive 40
miles to the freeway, recharge as he goes down the freeway, and then
drive another 40 miles without ever using any liquid fuel.

.. . .

You think the U. S. would continue to import a half trillion dollars a
year in oil when motorists could be powered from the grid?

If it is cheaper in the long run, yes.

Very very iffy at best considering the supply is diminishing and
global demand is increasing.

No one believes we'll be paying a half trillion in 2012.

It'll be more like $2 trillion / year.

If we are lucky.

As T. Boone Pickens pointed out, it's the greatest transfer of wealth
in the history of civilization.

And no one except you believes that we'ld continue to spend trillions
on over seas oil over the next 10 years when we didn't have to.

No matter what you do today, we will still have to for at least 10 years.

I don't deny that it may already be too late for many people to
survive soaring oil prices But this is no reason not to al least try.

Even if the entire highway system were somehow magically electrified
by tomorrow morning, it would take about 10 years before the majority
of existing vehicles were replaced.

We don't need every last fuel powered vehicle off the road
immediately.

With hybrids we can phase it in gradually thereby lessening the oil
shock.

It's critical that all new vehicles be series hybrids ASAP or we
really will be up the creek.

And you still have to be able to get out of your garage and to the
freeway, assuming you are going to use the freeway at all.

That's why the Volt has a 40 mile battery - only range.


Bret Cahill

 

[Androcles]

"John Fields" <jfields@austininstruments.com> wrote in message
news:vvqk251o7rb5ifrc43sdqss6htmqi43vmk@4ax.com...

On Sat, 6 Jun 2009 03:47:58 +0100, "Androcles"
Headmaster@Hogwarts.physics> wrote:


"John Fields" <jfields@austininstruments.com> wrote in message
news:7lkj25hof1airoq6rgodu1reqcupd0rj3p@4ax.com...
On Fri, 05 Jun 2009 20:35:23 -0500, john joseph <nowhere@nowhere.nl
wrote:

tgdenning@earthlink.net wrote:
On Jun 5, 7:28 pm, john joseph <nowh...@nowhere.nl> wrote:
tgdenn...@earthlink.net wrote:
On Jun 5, 3:02 pm, John Stafford <jstaff...@winona.edu> wrote:
On 6/5/09 1:26 PM, in article
o6idnVqzaun2_rTXnZ2dnUVZ_gJi4...@giganews.com,
"Bill Ward" <bw...@ix.REMOVETHISnetcom.com> wrote:
Again you've lost me---you are obviously misinterpreting what I
said.
Braking is done by the electric motor; for most of the braking
period
you are recovering the kinetic energy, which is why it is called
regenerative braking. The ultimate implementation would have no
disc
brakes at all. If you need further explanation please let me
know.
Motor/generators are transducers, not brakes. That means you can
only
slow down, not come to a complete stop. If the electronic
controller
failed, you couldn't even slow down. How big a market do you
expect
for
cars without brakes?
True. Thanks for the affirmation, Bill.
But motors can be reversed, and so you can certainly come to a
complete stop using only the motors. However, as I said, there can
be
a simple type of brake, since you need something for parking.
No they cannot! Not in real world applications! Try it! Try using
only
engine braking. Engine braking has far more stopping potential than
an
electric motor. But it still is far from enough!

I think maybe you are not reading carefully and just overreacting. I
said that electric motors can be reversed, which means that they have
as much 'stopping potential' as they have starting potential.

But they do not.

---
I'm not well versed in this field, so I'm asking: If the input to a DC
motor is shorted, once it's running, why would it take longer to stop it
than to run it up using a voltage source with a higher impedance than
the brake?
---
Huh?
If you short any motor, AC or DC, it will stop faster than you can finish
the word "stop".

---
My point exactly, which was directed at the "But they do not."

[have as much 'stopping potential' as they have starting potential]

comment.

Let us assume we apply a low voltage to an unloaded DC motor
and it takes 10 seconds to accelerate to 1000 RPM, overcoming
inertia (or we could just load it with a heavy flywheel or propel
a train). Force = mass * acceleration.
With a higher voltage we can reach 1000 RPM in 5 seconds,
we've increased the force so we increase the acceleration.
Now we disconnect the supply and short the terminals on the motor.
It grunts and stops in a few milliseconds no matter what voltage
we used to accelerate it. All the kinetic energy of the flywheel
or train is dissipated in the windings which heat up rapidly.
deceleration = -Force/mass.
Therefore they have MORE stopping potential than starting potential.

Incidentally, I've actually done this with a tapping machine that
was snapping taps as it cut threads and bottomed in a blind hole.
The usual solution is to break torque mechanically, but I tripped
the breaker on increased current as the motor slowed and shorted
the motor with normally closed contacts on the breaker.
That was many years ago.

 

[zzbunker@netscape.net]

On Jun 5, 1:21 pm, Bret Cahill <BretCah...@peoplepc.com> wrote:

Government pays to electrify 100,000 miles of freeway at a cost of $10
million/mile. Convenient grid powered coast to coast travel becomes
possible.

As there are roughly 210,000 lane miles of freeway in the US, what about
the other half?

The #1 and 2 lanes are for those who have already charged up in the #3
and # 4 lanes.

They are also for motorcyclists who don't want their tires to get
trapped in the slot, high mpg "clown cars" and rich folk who can
afford $25/gallon fuel.

$10 million/mile doesn't buy much more than paving these days.

Is that $10 million per mile or mile lane?

I suppose all the electification equipment capital and installation costs
are free?

By your numbers rebuilding the entire Eisenhower system would be 2.1
trillion.

We spend that every 4 years on foreign fuel.

The idiots don't know anything about that, Since the only thing the
idiots
even know about it is the Suez Canal. Which is why the people with
post 19th Century
brains build GPS, Cruise Missiles, AUVs, Thermo-Electric Cooling,
Microwave Cooling,
Atomic Clock Wristwatches, On-line Publishing, Biodiesel, and Gas
Turbine Engines rather
than train stations for the idiots anyway.

At $3/gallon fuel

By 2012 the payback time will be one year.

Now, maybe you have liver cancer or some other short life terminal
disease and gummint spending for something that has a 1 year payback
time is of no benefit to you.  You've already cashed out your 401 K.

In that case, we understand.

Bret Cahill

 

[Bret Cahill]

Kinetic energy increases with the square of velocity so regenerative
braking from 65 mph to 25 mph recoups up to 85% of the energy that
would otherwise be lost with friction braking.

There just isn't much energy to recoup at low speeds so friction
brakes are green at these speeds.

Regenerative braking is particularly valuable with heavy trucks on
long mountain grades. A one ton li-ion battery can get a 40 ton truck
up a 6,000 verticle ft climb and then be recharged on the descent.

A 80,000 lb truck going 45 mph down a 6% grade without compression or
regenerative braking must dissipate over a MW of heat in eight 50 lb
friction brake drums. Each drum is being heated 120 BTUs/sec but the
drum only has a total heat capacity of 5 BTUs/ degree F.

The temperature is increasing 25 degrees F every second.

After a few seconds the drums are red hot and the diameter increases
by an eighth of an inch and the brake pads no longer engage the drum.

The rabbits are all waiting at the bottom of the canyon hoping it's a
lettuce truck.


Bret Cahill

 

[John Fields]

On Sat, 6 Jun 2009 19:04:11 +0100, "Androcles"
<Headmaster@Hogwarts.physics> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:vvqk251o7rb5ifrc43sdqss6htmqi43vmk@4ax.com...
On Sat, 6 Jun 2009 03:47:58 +0100, "Androcles"
Headmaster@Hogwarts.physics> wrote:


"John Fields" <jfields@austininstruments.com> wrote in message
news:7lkj25hof1airoq6rgodu1reqcupd0rj3p@4ax.com...
On Fri, 05 Jun 2009 20:35:23 -0500, john joseph <nowhere@nowhere.nl
wrote:

tgdenning@earthlink.net wrote:
On Jun 5, 7:28 pm, john joseph <nowh...@nowhere.nl> wrote:
tgdenn...@earthlink.net wrote:
On Jun 5, 3:02 pm, John Stafford <jstaff...@winona.edu> wrote:
On 6/5/09 1:26 PM, in article
o6idnVqzaun2_rTXnZ2dnUVZ_gJi4...@giganews.com,
"Bill Ward" <bw...@ix.REMOVETHISnetcom.com> wrote:
Again you've lost me---you are obviously misinterpreting what I
said.
Braking is done by the electric motor; for most of the braking
period
you are recovering the kinetic energy, which is why it is called
regenerative braking. The ultimate implementation would have no
disc
brakes at all. If you need further explanation please let me
know.
Motor/generators are transducers, not brakes. That means you can
only
slow down, not come to a complete stop. If the electronic
controller
failed, you couldn't even slow down. How big a market do you
expect
for
cars without brakes?
True. Thanks for the affirmation, Bill.
But motors can be reversed, and so you can certainly come to a
complete stop using only the motors. However, as I said, there can
be
a simple type of brake, since you need something for parking.
No they cannot! Not in real world applications! Try it! Try using
only
engine braking. Engine braking has far more stopping potential than
an
electric motor. But it still is far from enough!

I think maybe you are not reading carefully and just overreacting. I
said that electric motors can be reversed, which means that they have
as much 'stopping potential' as they have starting potential.

But they do not.

---
I'm not well versed in this field, so I'm asking: If the input to a DC
motor is shorted, once it's running, why would it take longer to stop it
than to run it up using a voltage source with a higher impedance than
the brake?
---
Huh?
If you short any motor, AC or DC, it will stop faster than you can finish
the word "stop".

---
My point exactly, which was directed at the "But they do not."

[have as much 'stopping potential' as they have starting potential]

comment.

Let us assume we apply a low voltage to an unloaded DC motor
and it takes 10 seconds to accelerate to 1000 RPM, overcoming
inertia (or we could just load it with a heavy flywheel or propel
a train). Force = mass * acceleration.
With a higher voltage we can reach 1000 RPM in 5 seconds,
we've increased the force so we increase the acceleration.
Now we disconnect the supply and short the terminals on the motor.
It grunts and stops in a few milliseconds no matter what voltage
we used to accelerate it. All the kinetic energy of the flywheel
or train is dissipated in the windings which heat up rapidly.
deceleration = -Force/mass.
Therefore they have MORE stopping potential than starting potential.

Incidentally, I've actually done this with a tapping machine that
was snapping taps as it cut threads and bottomed in a blind hole.
The usual solution is to break torque mechanically, but I tripped
the breaker on increased current as the motor slowed and shorted
the motor with normally closed contacts on the breaker.
That was many years ago.

---
I've done the same thing on an orbital welder in order to make sure the
weld head is indexed properly at the end of a weld, but let's go back
and review what's going on here.

Somebody wrote:

"I think maybe you are not reading carefully and just overreacting. I
said that electric motors can be reversed, which means that they have
as much 'stopping potential' as they have starting potential."

That, to me, means that they can be stopped in _at least_ as much time
as it took to get them up to speed.

Then someone else wrote:

"But they do not."

That, to me, means that the poster thought a motor can't be stopped in
the time it took to run it up, and it would always have to take more
time.

Not believing the second poster, since I've plugged a few motors in my
time, I asked why it would take longer to stop the motor than to start
it.

Interestingly, you took exception to my position even though you agree
with it!

What's up with that?


JF

 

On Jun 6, 1:24 pm, Bret Cahill <BretCah...@peoplepc.com> wrote:

Kinetic energy increases with the square of velocity so regenerative
braking from 65 mph to 25 mph recoups up to 85% of the energy that
would otherwise be lost with friction braking.

There just isn't much energy to recoup at low speeds so friction
brakes are green at these speeds.

Regenerative braking is particularly valuable with heavy trucks on
long mountain grades.  A one ton li-ion battery can get a 40 ton truck
up a 6,000 verticle ft climb and then be recharged on the descent.

A 80,000 lb truck going 45 mph down a 6% grade without compression or
regenerative braking must dissipate over a MW of heat in eight 50 lb
friction brake drums.  Each drum is being heated 120 BTUs/sec but the
drum only has a total heat capacity of 5 BTUs/ degree F.

The temperature is increasing 25 degrees F every second.

After a few seconds the drums are red hot and the diameter increases
by an eighth of an inch and the brake pads no longer engage the drum.

The rabbits are all waiting at the bottom of the canyon hoping it's a
lettuce truck.

Bret Cahill

Ok Bret. So tell me why I don't want 4 small motors recharging 4
battery modules, on this truck, rather than a big honking motor and
battery pile that will need water cooling to deal with delta-T.

Surface area---another point for the modular side.

-tg

 

[Bill Ward]

On Sat, 06 Jun 2009 17:38:55 -0500, John Fields wrote:

On Sat, 6 Jun 2009 19:04:11 +0100, "Androcles"
Headmaster@Hogwarts.physics> wrote:


"John Fields" <jfields@austininstruments.com> wrote in message
news:vvqk251o7rb5ifrc43sdqss6htmqi43vmk@4ax.com...
On Sat, 6 Jun 2009 03:47:58 +0100, "Androcles"
Headmaster@Hogwarts.physics> wrote:


"John Fields" <jfields@austininstruments.com> wrote in message
news:7lkj25hof1airoq6rgodu1reqcupd0rj3p@4ax.com...
On Fri, 05 Jun 2009 20:35:23 -0500, john joseph <nowhere@nowhere.nl
wrote:

tgdenning@earthlink.net wrote:
On Jun 5, 7:28 pm, john joseph <nowh...@nowhere.nl> wrote:
tgdenn...@earthlink.net wrote:
On Jun 5, 3:02 pm, John Stafford <jstaff...@winona.edu> wrote:
On 6/5/09 1:26 PM, in article
o6idnVqzaun2_rTXnZ2dnUVZ_gJi4...@giganews.com, "Bill Ward"
bw...@ix.REMOVETHISnetcom.com> wrote:
Again you've lost me---you are obviously misinterpreting what
I said.
Braking is done by the electric motor; for most of the
braking period
you are recovering the kinetic energy, which is why it is
called regenerative braking. The ultimate implementation
would have no disc
brakes at all. If you need further explanation please let me
know.
Motor/generators are transducers, not brakes. That means you
can only
slow down, not come to a complete stop. If the electronic
controller
failed, you couldn't even slow down. How big a market do you
expect
for
cars without brakes?
True. Thanks for the affirmation, Bill.
But motors can be reversed, and so you can certainly come to a
complete stop using only the motors. However, as I said, there
can be
a simple type of brake, since you need something for parking.
No they cannot! Not in real world applications! Try it! Try
using only
engine braking. Engine braking has far more stopping potential
than an
electric motor. But it still is far from enough!

I think maybe you are not reading carefully and just overreacting.
I said that electric motors can be reversed, which means that they
have as much 'stopping potential' as they have starting potential.

But they do not.

---
I'm not well versed in this field, so I'm asking: If the input to a
DC motor is shorted, once it's running, why would it take longer to
stop it than to run it up using a voltage source with a higher
impedance than the brake?
---
Huh?
If you short any motor, AC or DC, it will stop faster than you can
finish the word "stop".

---
My point exactly, which was directed at the "But they do not."

[have as much 'stopping potential' as they have starting potential]

comment.

Let us assume we apply a low voltage to an unloaded DC motor and it
takes 10 seconds to accelerate to 1000 RPM, overcoming inertia (or we
could just load it with a heavy flywheel or propel a train). Force =
mass * acceleration. With a higher voltage we can reach 1000 RPM in 5
seconds, we've increased the force so we increase the acceleration. Now
we disconnect the supply and short the terminals on the motor. It grunts
and stops in a few milliseconds no matter what voltage we used to
accelerate it. All the kinetic energy of the flywheel or train is
dissipated in the windings which heat up rapidly. deceleration =
-Force/mass.
Therefore they have MORE stopping potential than starting potential.

Incidentally, I've actually done this with a tapping machine that was
snapping taps as it cut threads and bottomed in a blind hole. The usual
solution is to break torque mechanically, but I tripped the breaker on
increased current as the motor slowed and shorted the motor with
normally closed contacts on the breaker. That was many years ago.

---
I've done the same thing on an orbital welder in order to make sure the
weld head is indexed properly at the end of a weld, but let's go back
and review what's going on here.

Somebody wrote:

"I think maybe you are not reading carefully and just overreacting. I
said that electric motors can be reversed, which means that they have as
much 'stopping potential' as they have starting potential."

That, to me, means that they can be stopped in _at least_ as much time
as it took to get them up to speed.

Then someone else wrote:

"But they do not."

That, to me, means that the poster thought a motor can't be stopped in
the time it took to run it up, and it would always have to take more
time.

Not believing the second poster, since I've plugged a few motors in my
time, I asked why it would take longer to stop the motor than to start
it.

Interestingly, you took exception to my position even though you agree
with it!

What's up with that?

Some of the confusion may be due to the original claim of regenerative
braking. If you actively reverse current to the motors, you should
produce the same torque either direction, but at the cost of consuming
battery power.

Recovery of the decel energy requires some non-trivial impedance matching
to put it back into the battery, and would decrease in efficiency as the
velocity decreased, I would think. At zero, there would be no retarding
force.

IMHO, regenerative braking is a good idea, but it's not reliable enough
to be the primary braking system, because of its dependence on the
electronic controller. Initial brake pedal force should invoke
regeneration, but should be backed up by reliable hydraulic brakes past a
threshold force indicating driver dissatisfaction with current stopping
performance.

 

[Androcles]

"Bill Ward" <bward@ix.REMOVETHISnetcom.com> wrote in message
news:kL-dnS7kNMv4s7bXnZ2dnUVZ_jhi4p2d@giganews.com...

IMHO, regenerative braking is a good idea, but it's not reliable enough
to be the primary braking system, because of its dependence on the
electronic controller.

The is how Americans stop trains:
http://www.railway-technical.com/brake2.shtml#DynamicBrakes

Typically American, the energy as wasted as heat.

This is a British train:

http://ro.altermedia.info/images/eurostar-chunnel-train-4.jpg

Overhead is a catenary. It has a high voltage.

IYHO, regenerative braking is a good idea.
It's not your idea though.

What do you not think stops the Eurostar?

Your opinion, however honest it may be, is about as useful as a tit on a
bull.

 

[Bill Ward]

On Sun, 07 Jun 2009 04:56:03 +0100, Androcles wrote:

"Bill Ward" <bward@ix.REMOVETHISnetcom.com> wrote in message
news:kL-dnS7kNMv4s7bXnZ2dnUVZ_jhi4p2d@giganews.com...

IMHO, regenerative braking is a good idea, but it's not reliable enough
to be the primary braking system, because of its dependence on the
electronic controller.

The is how Americans stop trains:
http://www.railway-technical.com/brake2.shtml#DynamicBrakes

Typically American, the energy as wasted as heat.

This is a British train:

http://ro.altermedia.info/images/eurostar-chunnel-train-4.jpg

Overhead is a catenary. It has a high voltage.

IYHO, regenerative braking is a good idea. It's not your idea though.

What do you not think stops the Eurostar?

Your opinion, however honest it may be, is about as useful as a tit on
a bull.

Too bad you are so pathetic you need to snip context to appear to have a
point. But I'll give you a sorely needed clue - most people see right
through your dishonest tactic. I won't even bother to repost, I'll just
mention that the original subject was regenerative braking on
automobiles, and I was clearing up some confusion on the issue.

Trains were not at issue.

You are a disgrace to the good name of J. K. Rowling. Shame.

 

[qqq_qqq]

Bill Ward wrote:

On Sun, 07 Jun 2009 04:56:03 +0100, Androcles wrote:

"Bill Ward" <bward@ix.REMOVETHISnetcom.com> wrote in message
news:kL-dnS7kNMv4s7bXnZ2dnUVZ_jhi4p2d@giganews.com...

IMHO, regenerative braking is a good idea, but it's not reliable enough
to be the primary braking system, because of its dependence on the
electronic controller.
The is how Americans stop trains:
http://www.railway-technical.com/brake2.shtml#DynamicBrakes

Typically American, the energy as wasted as heat.

This is a British train:

http://ro.altermedia.info/images/eurostar-chunnel-train-4.jpg

Overhead is a catenary. It has a high voltage.

IYHO, regenerative braking is a good idea. It's not your idea though.

What do you not think stops the Eurostar?

Your opinion, however honest it may be, is about as useful as a tit on
a bull.

Too bad you are so pathetic you need to snip context to appear to have a
point. But I'll give you a sorely needed clue - most people see right
through your dishonest tactic. I won't even bother to repost, I'll just
mention that the original subject was regenerative braking on
automobiles, and I was clearing up some confusion on the issue.

Trains were not at issue.

You are a disgrace to the good name of J. K. Rowling. Shame.

Billowbwap: are you now bothering people in newsgroups other than
alt.global-warming after we successfully scared you away?

Hint: Bill needs the treatment, I mean THE treatment, where you confront
him with the facts.

Q

--
Ultimately to survive we should blow up our Moon, the particles
in orbit that remain help to combat global warming.

 

[Androcles]

"Bill Ward" <bward@ix.REMOVETHISnetcom.com> wrote in message
news:BZudndIIueoc0bbXnZ2dnUVZ_rSdnZ2d@giganews.com...

On Sun, 07 Jun 2009 04:56:03 +0100, Androcles wrote:

"Bill Ward" <bward@ix.REMOVETHISnetcom.com> wrote in message
news:kL-dnS7kNMv4s7bXnZ2dnUVZ_jhi4p2d@giganews.com...

IMHO, regenerative braking is a good idea, but it's not reliable enough
to be the primary braking system, because of its dependence on the
electronic controller.

The is how Americans stop trains:
http://www.railway-technical.com/brake2.shtml#DynamicBrakes

Typically American, the energy as wasted as heat.

This is a British train:

http://ro.altermedia.info/images/eurostar-chunnel-train-4.jpg

Overhead is a catenary. It has a high voltage.

IYHO, regenerative braking is a good idea. It's not your idea though.

What do you not think stops the Eurostar?

Your opinion, however honest it may be, is about as useful as a tit on
a bull.

Too bad you are so pathetic you need to snip context to appear to have a
point. But I'll give you a sorely needed clue - most people see right
through your dishonest tactic. I won't even bother to repost, I'll just
mention that the original subject was regenerative braking on
automobiles, and I was clearing up some confusion on the issue.

Actually the original subject was Fuel Savings from Roadbed
Electrification,
I'm so glad you've cleared up that confusion.

Trains were not at issue.

You are a disgrace to the good name of J. K. Rowling. Shame.

What do you not think stops the Eurostar?
(Ward's answer is a blank stare, not even a dropped jaw)

Fuck off, your miserable opinion is about as useful as a pitot tube on a
snail.

 

[Androcles]

"Bret Cahill" <BretCahill@peoplepc.com> wrote in message
news:0a342839-8210-43b0-8ff4-abb2e81276ff@f19g2000yqo.googlegroups.com...

The is how Americans stop trains:
?http://www.railway-technical.com/brake2.shtml#DynamicBrakes

Typically American, the energy as wasted as heat.

That's nothing.

You ought to see them water the banks of the freeway in the middle of
a "state of emergency" drought.

We might not have water to flush the toilet but, by golly, we're going
to look at something greener than brittle bush when we drive to work.


Bret Cahill
==========================================
Well, to be fair, American rail is not extensively electrified as it is here
so the energy has to be dumped somehow, but that's no excuse for
Ward's ignorant bigotry. That he imagines he can limit the debate
on energy efficiency referred to in the thread title to road vehicles
demonstrates the very narrow-mindedness he accuses others of.

He claims to have designed control systems and drivers for stepper
motors but hasn't ever seen one used for vehicle propulsion or
regeneration, and also claims "regenerative braking is a good idea,
but it's not reliable enough to be the primary braking system,
because of its dependence on the electronic controller."

If he really was as capable as he boasts he'd design a controller
for a car.
The guy is not even a decent devil's advocate pointing out what the
problems might be, he's an opinionated fuckwit still living in the
20th century.

 

[Bret Cahill]

Too bad you are so pathetic you need to snip context to appear to have a
point. �But I'll give you a sorely needed clue - most people see right
through your dishonest tactic. �I won't even bother to repost, I'll just
mention that the original subject was regenerative braking on
automobiles, and I was clearing up some confusion on the issue.

Actually the original subject was �Fuel Savings from Roadbed
Electrification,
�I'm so glad you've cleared up that confusion.

That's nothing. One poster has been insisting for over a week that
the soaring cost of oil is irrelevant to the cost of electrification.
It makes you wonder why he even clicked on this thread in the first
place.

Is some virus going around that compromises their basic reasoning
ability?

Are these people really this dumb/irrational in person and if so, how
do I manage to avoid meeting them on the street?

Maybe their case workers have them all posting here to _keep_ them off
the street.

If that's true then it's a good thing.


Bret Cahill

 

[Bret Cahill]

The is how Americans stop trains:
�http://www.railway-technical.com/brake2.shtml#DynamicBrakes

Typically American, the energy as wasted as heat.

That's nothing.

You ought to see them water the banks of the freeway in the middle of
a "state of emergency" drought.

We might not have water to flush the toilet but, by golly, we're going
to look at something greener than brittle bush when we drive to work.


Bret Cahill