In article ,
Johny B Good wrote:
However, braking a car savagely from high speed is a very different
matter. The energy produced has to be dissipated somehow. Shorting the
motor and locking the wheels as suggested by NP doesn't seem ideal to me.

It isn't. It was just a point being made on the effectiveness of
regenerative braking. A real system doesn't simply short the motor
out, it uses the motor in 'generator mode' to absorb the energy into a
battery or supercap rather than have it simply dissipated as waste
heat in a brake disk.

And as I keep on saying that's not going to be able to cope with a panic
stop from high speed.

The brakes on most cars are designed for just that - a panic stop from its
maximum speed. So well over specced for normal use in this country if you
stick to the speed limit.

--
*Hang in there, retirement is only thirty years away! *

Dave Plowman London SW
To e-mail, change noise into sound.

On 27/04/14 08:47, Tim Lamb wrote:
In message , Johny B Good
writes
The only other transmission method that occurs to me that might
compete with an all electric transmission is the use of hydraulic hub
motors in each wheel connected to a pump driven by a common motor[2].
A variable delivery swash plate type pump can provide a variomatic
auto transmission system with no need for a seperate clutch. I haven't
seen any comparative data on such a scheme though.

I think the transmission losses in a hydraulic system are on a par
with those in a conventional mechanical system. The costs are likely
to be considerably higher to produce an all hydraulic transmission
(even in mass production) for something as humble as the family car so
even assuming a similar transmission efficiency between the two
systems, it's not going to happen in anything other than specialised
vehicles (plough pulling tractors and Space Shuttle Transporters)
where the high precision of control outweighs the extra cost.

International Harvester brought out a tractor with just this system,
around 1975. I drove one here on trial. Bl--dy noisy!

I think hydraulic transmissions is MASSIVELY more lossy than a gearbox
or we would all be using it.

a good gear train should be at design load up in the high 97% range.

Its perry hard to get a hydraulic transmissions much more than 80-90%
which is why it is seldom used except when its huge advantages -
infintely variable ratios small and light motors and ability to drive
power through flexible pipes - make it more desirable than a more
efficient multi-ratio gearbox.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 27/04/14 10:35, Dave Plowman (News) wrote:
In article ,
Johny B Good wrote:
Oh yes it is.

you put a short across a leccy motor and it stops dead in its tracks mate.

I can certainly attest to that phenomenon from my own experience with
designing and building a controller board for a Philips solenoid
controlled bi-directional data cassette drive which used seperate cush
drive high quality permanent magnet DC motors (using proper carbon
brushes) on the tape drive hubs. This phenomena becomes ever more
extreme as you inrease the motor size.

On a car it is usual to short the wiper motor when it parks to make sure
they don't overshoot.

However, braking a car savagely from high speed is a very different
matter. The energy produced has to be dissipated somehow. Shorting the
motor and locking the wheels as suggested by NP doesn't seem ideal to me.

I never advocated that, merely demonstrated that that way the tprque you
claimed couldn't be achieved, could be achieved.

In practice with a battery of adequate size you take the genereated
output of the traction motor and pass it through an up converter to
charge the battery, controlling the power drawn by the convertible to
provide the desired braking.

In theory you can have a totally 'cool' braking system with idealised
components and zero resistance windings. In practice resistive losses
will result in SOME heat being generated, and then the issue is down to
how much is tolerable in terms of short duration emergency brakes and so on.

But the aim is to dump most of the energy back into the battery, not
into brakes, leaving them more or less as a 'handbrake' suitable for
keeping the vehicle stopped and secondly to deal with the situation in
which speeds are so low that its not practical t up convert the output
if the motor to fully stop it BUT even that can be catered for by
putting the system into 'reverse; and using the battery itself to retard
motion.

As you are aware current F1 power trains are using this technology to
add up to 40bhp of electrical power to the system and using
regenerative braking to pull it off the rear wheels (with some deep
issues in terms of how that affects overall brake balance)

It's far from the ideal for a road car, or remotely near where it has to
be, but its for sure being developed with that in mind. 40bhp is more
than enough for a small town car, and if the stop start nature of town
driving can harvest even 50% of the braking it's a huge increase in
effective range.

There is a massive amount of development in progress, and a '85% plus'
harvest of all braking into a battery is a long way off, but the point
I was trying to make is that it COULD be done. It wasn't just a case of
'never get enough torque' because patently you can. In the limit a
sliding tyre and a locked wheel requires NO power dissipation in the
motor or braking system. Its all now in the tyre..





--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 27/04/14 12:10, Dave Plowman (News) wrote:
In article ,
Johny B Good wrote:
However, braking a car savagely from high speed is a very different
matter. The energy produced has to be dissipated somehow. Shorting the
motor and locking the wheels as suggested by NP doesn't seem ideal to me.

It isn't. It was just a point being made on the effectiveness of
regenerative braking. A real system doesn't simply short the motor
out, it uses the motor in 'generator mode' to absorb the energy into a
battery or supercap rather than have it simply dissipated as waste
heat in a brake disk.

And as I keep on saying that's not going to be able to cope with a panic
stop from high speed.

And no mater how much you keep saying it, you are in fact wrong.


The brakes on most cars are designed for just that - a panic stop from its
maximum speed. So well over specced for normal use in this country if you
stick to the speed limit.


Actually they are not even specced for that.

You need something in the upper class of sports saloon to get that
without real fading. Especially downhill.

------------------------------------------------------------

Some numbers may be worth illustrating:

2 tonnes of let's say BMW at 100mph.

KE is 1/2 m v squared so that 160kmh squared or 1975 meters per second
squared times 1000 kg which is 1.975 megajoules which is 7.1 kWh.

That is NOT a lot.

At 1g braking, the peak power flow is, over the first second when speed
has to come down from 44.44 m/s to 34.64. m/s. is about 775KW give or
take. (about 1000 bhp).

Now a big Beemer already has an engine up in the 2-300bhp range to get a
2 tonne car to 100mph at a reasonable speed. So we could say that we
therefore need an equivalent electric motor capable of taking a 3:1 to
5:1 overload for ONE SECOND. and progressively less overload in the next
second and so on. That is eminently reasonable.

And the same goes for its controller or upconverter electronics.

These are NOT big or insoluble problems.

A battery that will take it that fast or a supercapacitor is a bigger
problem however. If we think of a 50 kWh traction battery it has a one
hour charge rate of 50KW, and we want to put 15 times that rate into it.
That's where a supercapacitor might actually work. So how BIG does a
supercapacitor have to be at say 400V to store a braking energy of 7Kwh?

energy in a capacitor in joules is 1/2 CV^2

we know we need to store 2MJ give or take in TOTAL - we can put SOME
into the battery, but lets have a capacitor for MOST of it.

V^2 = 160000 (400 squared)

so rearranging capacitor in farads is 1000000/160000 = 6.25 Farads

Or 6250000 uF :-)

super capacitors of that sort of energy storage are around with internal
resistances in the milliohm range,


They are in fact being employed by model car racers to give a bit of
extra surge to an accelerating car..because a super capacitor in
parallel with a battery has a hugely increased PEAK power.


So it's all within range really of development. Its not pie-in the sky
or requiring some undreamed of technology, as is for example renewable
energy storage. We are NOT looking for a lot of storage: just one that
can absorb the peaks.

What we need is a braking system that can at least match disc brakes -
and I would suggest that very few braking systems can do 1g at 100mph
outsider of the race track - and that requires a motor and control
system that can handle a 3 or 5 to one overload for a few seconds and
something that can absorb charge at a similarly higher rate than the
traction battery can put out.

Of course the first thing you do when moving off is to drain the super
capacitor in acceleration! then it's nice and flat if you need the
brakes. IN theory you could keep the capacitor in such a state of charge
that it could always absorbed a full emergency stop from the speed you
are going. "Capacitor to accelerate and decelerate, battery for cruising"

The F1 boys MUST be using something like this as their systems appear to
charge and discharge several times a circuit. And I know of no battery
that can in fact do that.

I do admit that batteries that will allow 500+ mile range will always be
pie in the sky, for at lest 15-20 years but a 200 mile range car built
very hi tech and using good regeneration, lightweight body and skinny
tyres - a sort of hi tech 2CV - or a hybrid that really start to get
near the 100mpg bracket, is just about within reach.

And maybe, just maybe super capacitors will start to get near batteries
in terms of energy density.



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Sun, 27 Apr 2014 12:10:35 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
However, braking a car savagely from high speed is a very different
matter. The energy produced has to be dissipated somehow. Shorting the
motor and locking the wheels as suggested by NP doesn't seem ideal to me.

It isn't. It was just a point being made on the effectiveness of
regenerative braking. A real system doesn't simply short the motor
out, it uses the motor in 'generator mode' to absorb the energy into a
battery or supercap rather than have it simply dissipated as waste
heat in a brake disk.

And as I keep on saying that's not going to be able to cope with a panic
stop from high speed.

It's a rather interesting stance that you take. On the one hand you
agree with TNP's assertion that 'shorting a motor' can result in
locked up wheels (so acknowledging the more than ample braking effect
of such electrodynamic braking), decrying such extreme braking as
being a 'Bad Thing' (which is not in dispute) and, otoh, claiming that
it won't cope with emergency stops from high speed (the very speed
region where such electrodynamic braking is at its most effective).


The brakes on most cars are designed for just that - a panic stop from its
maximum speed. So well over specced for normal use in this country if you
stick to the speed limit.

That's certainly been true for the past 3 decades or so for one off
emergency braking events. The fact that the brakes aren't up to race
conditions of use but perfectly fine for normal driving on public
roads and highways should suggest that the hub motors in an AWD
electric vehicle will likewise be perfectly able to cope with such
extremes of use.

What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

Most of the 'waste energy' is soaked up by a suitable rechargable
battery or else diverted to a substantial heatsinked resistive load
to protect the KERS battery from being dangerously overcharged _away_
from the wheels and the secondary hydraulic braking system components
at each wheel.

When you add to this the fact that the KERS control from a central
power management and control unit can intelligently control the
braking force applied by each individual wheel to avoid wheel lockup
and maintain balanced braking to prevent an out of control skid far
better than any retro add on to a hydraulic braking system, you should
see that such high speed emergency braking becomes as safe as it
possibly can be by the use of this technology.

Furthermore, unlike the 'cooked brakes' syndrome of conventional
disks, you can set off again and immediately repeat the process
without 'brake fade' kicking in on your next attempt (and all
subsequent attempts for that matter).

Contrary to your argument that electrodynamic braking cannot cope
with emergency stops from high speed, it turns out that this is the
ideal way to maximise safety under such extreme braking conditions. In
short, you couldn't be more wrong in making such an assertion.
--
Regards, J B Good

On 25/04/2014 11:35, Tim Streater wrote:
You'll be telling us next that because we have been told that
such-and-such wind farm will generate "enough power for xxx homes",
that it will actually do so.

But it will.

Occasionally

Andy

On 26/04/2014 13:09, Dave Plowman (News) wrote:
FFS, a train takes ages to stop. Lack of friction between the wheels and
track. Nothing like a vehicle on a road. Which can better 1G when braking.

Apparently the coefficient of friction steel-steel is about 0.5-0.8 -
which would give them braking as good as a truck. Or a Disco.

Not as good as a decent car though.

Andy

On 27/04/2014 20:08, Johny B Good wrote:
Contrary to your argument that electrodynamic braking cannot cope
with emergency stops from high speed, it turns out that this is the
ideal way to maximise safety under such extreme braking conditions. In
short, you couldn't be more wrong in making such an assertion.

If you google for "Electric retarder" (no quotes) you'll get lots of
stuff about electric braking systems for commercial vehicles.

Andy

On Sun, 27 Apr 2014 13:32:16 +0100, Tim Streater
wrote:

In article , Johny B Good
wrote:

brushes) on the tape drive hubs. This phenomena becomes ever more
extreme as you inrease the motor size.

Phenomenon. (see other thread).

Mea culpa! :-(
--
Regards, J B Good

In article ,
The Natural Philosopher wrote:
And as I keep on saying that's not going to be able to cope with a panic
stop from high speed.

And no mater how much you keep saying it, you are in fact wrong.

Luckily, you don't design cars. Otherwise the accident rate would be on a
steep curve.

--
*Verbs HAS to agree with their subjects *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.

--
*I feel like I'm diagonally parked in a parallel universe*

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 27 Apr 2014 23:51:47 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.

If we're talking about a family car with comparable acceleration
performance to that of a mid specced ICE powered car, then peak
acceleration will be limited by tyre grip, say a tad over 1G. The same
tyre grip consideration applies on deceleration so the same peak motor
current limit applies.

The major issue isn't with the hub motors, it's in regard to how you
dispose of that high energy surge from the recovered kinetic energy.
Ideally, none of it should go to waste but, under emergency
conditions, a significant portion might have to be dumped into a
resistive load during the first second or three of such an extreme
braking manouver from high speed.

The KERS used by F1 cars was only a bolt on afterthought. The KERS
unit only provided an additional 10 to 15% power boost (80BHP afair)
and therefore doesn't contribute as much braking force as you can get
when the prime mover is all electric.

The rules and technology used for the current season have changed
significantly according to the info page in this link:

http://www.formula1.com/inside_f1/understanding_the_sport/5280.html

HTH & HAND
--
Regards, J B Good

On 27/04/14 23:50, Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
And as I keep on saying that's not going to be able to cope with a panic
stop from high speed.

And no mater how much you keep saying it, you are in fact wrong.

Luckily, you don't design cars. Otherwise the accident rate would be on a
steep curve.

what makes you think I dont?

I see that faced with the exact calculations necessary to prove that
dynamic braking is capable of stopping a car perfectly adequately, you
simply resort or ad hominem personal abuse.,

By their actions shall ye know them

I've been designing things that WORKED all my life.

Over a very wide field indeed.

I've got a bloody cambridge DEGREE in designing stuff that works.

What have you got? a 3rd rate technicians qually, attitude, and a chip
on your shoulder.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 27/04/14 23:51, Dave Plowman (News) wrote:
In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.


It would be up to about 50mph for powerful sports car or sports saloon.
At 100mph as I pointed out its 3-5 times higher.

That isn't nonsense, that's a reasonable overload.

I accept that you cant do the calculations that I laid out, but you
might at least have the grace to accept the results.

Except you are a graceless **** with attitude...

--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

In article ,
Johny B Good wrote:
On Sun, 27 Apr 2014 23:51:47 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.

If we're talking about a family car with comparable acceleration
performance to that of a mid specced ICE powered car, then peak
acceleration will be limited by tyre grip, say a tad over 1G. The same
tyre grip consideration applies on deceleration so the same peak motor
current limit applies.

There is no family car ever built where it will break traction through
engine torque. But even the most basic is capable of doing that by hard
braking if it doesn't have ABS, etc.

To get *any* car which will accelerate as fast as it brakes means going
for some very exotic machinery indeed.

--
*How about "never"? Is "never" good for you?

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
The Natural Philosopher wrote:
On 27/04/14 23:50, Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
And as I keep on saying that's not going to be able to cope with a panic
stop from high speed.

And no mater how much you keep saying it, you are in fact wrong.

Luckily, you don't design cars. Otherwise the accident rate would be
on a steep curve.

what makes you think I dont?

I see that faced with the exact calculations necessary to prove that
dynamic braking is capable of stopping a car perfectly adequately, you
simply resort or ad hominem personal abuse.,

Covering a page with calculations to prove part of an argument is the
oldest trick in the book. But even with those you admit that what do do
with the energy generated is the real problem.


By their actions shall ye know them

I've been designing things that WORKED all my life.

Over a very wide field indeed.

I've got a bloody cambridge DEGREE in designing stuff that works.

What have you got? a 3rd rate technicians qually, attitude, and a chip
on your shoulder.

And most of your ideas are theories based on what might be possible if a
major stumbling block is overcome. Ie, half baked.

--
*All those who believe in psychokinesis, raise my hand *

Dave Plowman London SW
To e-mail, change noise into sound.

On 28/04/2014 10:42, Dave Plowman (News) wrote:
In article ,
Johny B Good wrote:
On Sun, 27 Apr 2014 23:51:47 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.

If we're talking about a family car with comparable acceleration
performance to that of a mid specced ICE powered car, then peak
acceleration will be limited by tyre grip, say a tad over 1G. The same
tyre grip consideration applies on deceleration so the same peak motor
current limit applies.

There is no family car ever built where it will break traction through
engine torque. But even the most basic is capable of doing that by hard
braking if it doesn't have ABS, etc.

To get *any* car which will accelerate as fast as it brakes means going
for some very exotic machinery indeed.

JBG and TNP have missed the difference between force and power. It
doesn't take much power to break traction from stationary, but the
amount required goes up as you get faster.

Similarly the amount of power you need to dissipate in a brake goes up
as you get faster. To slow a 1.5 tonne car at 70mph at 1G requires you
to dissipate 460KW or 620 HP. If your windings aren't built to provide
that kind of input power, they're not going to cope with shoving it back
out again.

Referring to train braking isn't that helpful - sure, powered units may
have dynamic braking, but that's not enough for the rest of the train.

On 28/04/14 10:42, Dave Plowman (News) wrote:
In article ,
Johny B Good wrote:
On Sun, 27 Apr 2014 23:51:47 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.

If we're talking about a family car with comparable acceleration
performance to that of a mid specced ICE powered car, then peak
acceleration will be limited by tyre grip, say a tad over 1G. The same
tyre grip consideration applies on deceleration so the same peak motor
current limit applies.

There is no family car ever built where it will break traction through
engine torque.

Rubbish. Even my old Bedford CA MkII VAN would do that below 5mph.

Conversely there are very few family cars that will lock wheels at 70mph
either.


But even the most basic is capable of doing that by hard
braking if it doesn't have ABS, etc.

Not at 70mph. try it.

To get *any* car which will accelerate as fast as it brakes means going
for some very exotic machinery indeed.

Or an electric motor and a supercapcitor.,



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 28/04/14 10:49, Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
On 27/04/14 23:50, Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
And as I keep on saying that's not going to be able to cope with a panic
stop from high speed.

And no mater how much you keep saying it, you are in fact wrong.

Luckily, you don't design cars. Otherwise the accident rate would be
on a steep curve.

what makes you think I dont?

I see that faced with the exact calculations necessary to prove that
dynamic braking is capable of stopping a car perfectly adequately, you
simply resort or ad hominem personal abuse.,

Covering a page with calculations to prove part of an argument is the
oldest trick in the book. But even with those you admit that what do do
with the energy generated is the real problem.

The first part was to refute your statement that an electric motor could
not do what disk brakes could.

I take it you accept that you were totally wrong?

A far as waht to do wit the energy goes well I was merely shoing that
there are some hurdles to overcome if you want to REUSE it.

If you dump it into a radiatior via a resistor and blow a fan on that
it really isn't a problem.

Its probably BETTER than disk brakes which cant store that much heat
before fading.



By their actions shall ye know them

I've been designing things that WORKED all my life.

Over a very wide field indeed.

I've got a bloody cambridge DEGREE in designing stuff that works.

What have you got? a 3rd rate technicians qually, attitude, and a chip
on your shoulder.

And most of your ideas are theories based on what might be possible if a
major stumbling block is overcome. Ie, half baked.


No they are not. I am careful to give a balanced approach showing what
isn't a stumbling block (torque) and what is (storage, if you want the
energy back).

I don't make bland qualitative statements based on ignorance and
prejudice. I make carefully qualified statements based on science
technology and engineering as it exists today.




--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 28/04/14 12:52, Clive George wrote:
On 28/04/2014 10:42, Dave Plowman (News) wrote:
In article ,
Johny B Good wrote:
On Sun, 27 Apr 2014 23:51:47 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load
current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.

If we're talking about a family car with comparable acceleration
performance to that of a mid specced ICE powered car, then peak
acceleration will be limited by tyre grip, say a tad over 1G. The same
tyre grip consideration applies on deceleration so the same peak motor
current limit applies.

There is no family car ever built where it will break traction through
engine torque. But even the most basic is capable of doing that by hard
braking if it doesn't have ABS, etc.

To get *any* car which will accelerate as fast as it brakes means going
for some very exotic machinery indeed.

JBG and TNP have missed the difference between force and power. It
doesn't take much power to break traction from stationary, but the
amount required goes up as you get faster.


I most certainly have NOT.

See the maths where I absolutely never mentioned force, is buried in et
equations for 1 g decelerations and isn't something that need be
mentioned - its obvious that to stop a car weighing 2 tonnes at 1g takes
tow tonnes(force) applied.


What is impportnt is not the force, its what the total energy and peak
power generated is BY that force as thatt defines the size of the store
and the size of the kit to transfer energy to the stire.


Similarly the amount of power you need to dissipate in a brake goes up
as you get faster. To slow a 1.5 tonne car at 70mph at 1G requires you
to dissipate 460KW or 620 HP. If your windings aren't built to provide
that kind of input power, they're not going to cope with shoving it back
out again.


I assumed that was in fact something everybody knew - even Plowperson.
So not even worth mentioning.

You seem not to have even read waht I wrote.

Summarised: about 7Kwh of energy to be stored or dumped from a 2 tonne
car travelling at 100mph to bring it to a stop.

Peak power flows of around 1000 bhp (750 KW) at the onset of braking.

1000BHP for a few instants is not that hard for a 200bhp motor that has
to be efficient at 200bhp.

(Or actually 4x50 bhp motors as we were talking about in wheel drive).

Theres a further interesting fact.

The actual torque generated by the motor is proportional to current, so
what we see in a smooth 1g deceleration is the same current flowing
through the windings as the braking happens and the output voltage
falling as the wheel RPM drops.

So the heat lost IN the motor is constant throughout the braking phase
- its the heat or power taken OUT of the motors as a generator that
varies with time.

We are in fact looking at a 5:1 at most current increase from 'peak
power' to 'peak braking'. 3 or4:1 more likely.

Say the motor is 95% efficient at peak power. Pretty crap as electric
motors go, but probably about right. 10% of the power is lost as heat.
that means that in the limit under braking is going to see 3-5 times
that, so 15-25% of the power lost as heat.

If you want to lose less, use more copper. And get more energy back.

Its a trade off between weight and performance and recovered energy.

BUT mostly you wont be using emergency stop braking so in the end you
will probably let the motor get a bit hot and suffer loss of recovered
energy in order to optimise costs and range for the 'normal' case.

IN the worst case the motor will simply get as hot as a disk brake
would, and that is within range of a cobalt magnet, if not neodymium.

(I've had a cobalt motor unsolder itself, but the magnets and (spot
welded) windings survived)...


We can do a bit more generic back of envelope stuff. Model aircraft
motors are probably the most efficient in terms of power to weight that
you are likely to come across. so lets see what a cooking garde motor is
in terms of power to weight, and work on 4x250 bhp motors. so absolutely
capable of taking the braking load.

http://www.modelmotors.cz/index.php?...e=20&line=GOLD

here we have a motor capable of handling 65A for 20 seconds off about a
40V supply. 2.6KW

It weighs 1.3kg.so 2KW per kg.


So in terms of meeting our one per wheel target of 750KW we need about
175KW per wheel and that comes to 87.5kg per wheel. For a motor that
can DEFINITELY generate ALL of that power for 20 seconds!! That's heavy,
BUT we are not wildly out of the ballpark.

And its a neodymium motor which cannot take even 100C heat.

use cobalt add cooling and it gets a lot better. Or use an
electromagnet for the field windings..

Nope. Its tough, but I don't thunk its out of order to end up with a
wheel around the 25kg mark that would do the job.


If the weight gets too great - well move it inboard then.And water cool it,



Referring to train braking isn't that helpful - sure, powered units may
have dynamic braking, but that's not enough for the rest of the train.


Well exactly. Train brakes are pretty crap by and large.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Mon, 28 Apr 2014 13:12:29 +0100, The Natural Philosopher wrote:

Conversely there are very few family cars that will lock wheels at 70mph
either.

Really...?

In article ,
Clive George wrote:
There is no family car ever built where it will break traction through
engine torque. But even the most basic is capable of doing that by hard
braking if it doesn't have ABS, etc.

To get *any* car which will accelerate as fast as it brakes means going
for some very exotic machinery indeed.

JBG and TNP have missed the difference between force and power. It
doesn't take much power to break traction from stationary, but the
amount required goes up as you get faster.

You can break traction through savage use of the clutch - but that is
using kinetic energy for that one task - not the constant torque from the
power source. Although of course once traction is lost is takes less
torque to maintain that state.

Similarly the amount of power you need to dissipate in a brake goes up
as you get faster. To slow a 1.5 tonne car at 70mph at 1G requires you
to dissipate 460KW or 620 HP. If your windings aren't built to provide
that kind of input power, they're not going to cope with shoving it back
out again.

My thoughts too. It would also depend on the motor being an equally
efficient generator - one of the other things conveniently omitted.

Referring to train braking isn't that helpful - sure, powered units may
have dynamic braking, but that's not enough for the rest of the train.

As I said the peak retardation of a train isn't in the same ballpark as a
car - if it was you couldn't have standing passengers.

I'd take this opportunity of reminding everyone that NP suggested you
could all but get rid of a conventional brake. Not even a train manages
that. And the (rare) electric fast car still has brakes comparable to an
IC engined one. Even they realise is maximum breaking effort in an
emergency is not something you experiment with.

--
*Husband and cat lost -- reward for cat

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
The Natural Philosopher wrote:
There is no family car ever built where it will break traction through
engine torque.

Rubbish. Even my old Bedford CA MkII VAN would do that below 5mph.

You really are a fool, aren't you?

--
*Yes, I am an agent of Satan, but my duties are largely ceremonial

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Adrian wrote:
On Mon, 28 Apr 2014 13:12:29 +0100, The Natural Philosopher wrote:

Conversely there are very few family cars that will lock wheels at
70mph either.

Really...?

I often wonder if he actually drives. ;-)

--
*Strip mining prevents forest fires.

Dave Plowman London SW
To e-mail, change noise into sound.

On 28/04/14 14:46, Dave Plowman (News) wrote:
In article ,
Adrian wrote:
On Mon, 28 Apr 2014 13:12:29 +0100, The Natural Philosopher wrote:

Conversely there are very few family cars that will lock wheels at
70mph either.

Really...?

I often wonder if he actually drives. ;-)

with antilock brakes..


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

In article ,
The Natural Philosopher wrote:
On 28/04/14 14:46, Dave Plowman (News) wrote:
In article ,
Adrian wrote:
On Mon, 28 Apr 2014 13:12:29 +0100, The Natural Philosopher wrote:

Conversely there are very few family cars that will lock wheels at
70mph either.

Really...?

I often wonder if he actually drives. ;-)

with antilock brakes..

On ice too - to suit your arguments. ;-)

--
*If horrific means to make horrible, does terrific mean to make terrible?

Dave Plowman London SW
To e-mail, change noise into sound.

On 28/04/14 14:46, Dave Plowman (News) wrote:
In article ,
Adrian wrote:
On Mon, 28 Apr 2014 13:12:29 +0100, The Natural Philosopher wrote:

Conversely there are very few family cars that will lock wheels at
70mph either.

Really...?

I often wonder if he actually drives. ;-)

If you ACTUALLY look at rad test on even GOOD cars you will find that
about 1.1g is as good as a top performance car gets from 70ph o a dry
road. That's around 156 feet stopping distance.

You may lock the wheels at lower speeds than 50mph, but seldom higher
than that.

Try it.




--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Mon, 28 Apr 2014 15:19:11 +0100, The Natural Philosopher wrote:

Conversely there are very few family cars that will lock wheels at
70mph either.

Really...?

I often wonder if he actually drives. ;-)

If you ACTUALLY look at rad test on even GOOD cars you will find that
about 1.1g is as good as a top performance car gets from 70ph o a dry
road.

Care to explain the relevance between that and whether the brakes can/
will lock the wheels?

Or even the role that ABS plays in whether the wheels will lock or not?

In article ,
The Natural Philosopher wrote:
On 28/04/14 14:46, Dave Plowman (News) wrote:
In article ,
Adrian wrote:
On Mon, 28 Apr 2014 13:12:29 +0100, The Natural Philosopher wrote:

Conversely there are very few family cars that will lock wheels at
70mph either.

Really...?

I often wonder if he actually drives. ;-)

If you ACTUALLY look at rad test on even GOOD cars you will find that
about 1.1g is as good as a top performance car gets from 70ph o a dry
road. That's around 156 feet stopping distance.

But not with locked wheels. The stopping distance would be considerably
longer with that.

You may lock the wheels at lower speeds than 50mph, but seldom higher
than that.

Try it.

I often wonder if you actually drive.

--
*The most wasted day of all is one in which we have not laughed.*

Dave Plowman London SW
To e-mail, change noise into sound.

On 28/04/2014 15:18, Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
On 28/04/14 14:46, Dave Plowman (News) wrote:
In article ,
Adrian wrote:
On Mon, 28 Apr 2014 13:12:29 +0100, The Natural Philosopher wrote:

Conversely there are very few family cars that will lock wheels at
70mph either.

Really...?

I often wonder if he actually drives. ;-)

with antilock brakes..

On ice too - to suit your arguments. ;-)

The load on the braking system is higher with ABS than without anyway.
The energy goes into the brakes rather than the tyres.

Referring to train braking isn't that helpful - sure, powered units may
have dynamic braking, but that's not enough for the rest of the train.

Sometimes but not always remember the underground have used this for a
very long time now as do some of the more modern EMU units..


Well exactly. Train brakes are pretty crap by and large.

Due to the actual brake system or the steel wheel on steel rails?...



--
Tony Sayer

In article ,
tony sayer wrote:
Well exactly. Train brakes are pretty crap by and large.

Due to the actual brake system or the steel wheel on steel rails?...

It's not that long ago they had simple brake blocks. Then they got discs -
long after they were common on cars.

--
*Cleaned by Stevie Wonder, checked by David Blunkett*

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 28 Apr 2014 12:52:18 +0100, Clive George
wrote:

On 28/04/2014 10:42, Dave Plowman (News) wrote:
In article ,
Johny B Good wrote:
On Sun, 27 Apr 2014 23:51:47 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.

If we're talking about a family car with comparable acceleration
performance to that of a mid specced ICE powered car, then peak
acceleration will be limited by tyre grip, say a tad over 1G. The same
tyre grip consideration applies on deceleration so the same peak motor
current limit applies.

There is no family car ever built where it will break traction through
engine torque. But even the most basic is capable of doing that by hard
braking if it doesn't have ABS, etc.

To get *any* car which will accelerate as fast as it brakes means going
for some very exotic machinery indeed.

Electric motor not 'exotic' enough then?


JBG and TNP have missed the difference between force and power. It

I haven't missed that distinction.

doesn't take much power to break traction from stationary, but the
amount required goes up as you get faster.

Torque output from a motor very closely approximates the current draw
which is the limiting factor when it comes to I squared R losses and
peak power output is determined by the maximum rpm limitation which
also approximates to the applied voltage. Similar limitations also
apply when the motor is acting as a generator in a KER system.


Similarly the amount of power you need to dissipate in a brake goes up
as you get faster. To slow a 1.5 tonne car at 70mph at 1G requires you
to dissipate 460KW or 620 HP. If your windings aren't built to provide
that kind of input power, they're not going to cope with shoving it back
out again.

Assuming the direct drive motor is designed to cope with sustained
maximum cruising speeds and capable of providing an initial 1G
acceleration, it will be guaranteed to cope with deceleration
stresses.

Your figures looked to be 'about right' initially but I thought it
best to calculate the peak horse power for myself and it turns out to
be a more modest 566.7 BHP. You've over estimated it by nearly 10%
(discrepency is actually 9.4% greater).

This isn't a large error but it does suggest you're trying to big up
the problem of high transient power delivery rate to better favour
your argument.

Assuming a constant deceleration of 1G, it will take 3.2 seconds to
come to a standstill. The motor winding current will be constant
whilst the voltage output falls linearly with reduction in speed. The
I squared R motor winding losses will therefore be essentially
constant over the deceleration period (3.2 seconds) whilst the average
power output will be half the peak (283 BHP).

Translating into watts we get 211.4 KW and into joules we get 676.44
Kj during the 3.2 seconds worth of braking to a standstill which is
enough energy to bring 2 litres of water to the boil from a starting
temperature of 20deg C.

The main issue in contention is the torque stress induced I squared R
losses in the motor windings. Handling the recovered energy is a
seperate but not insurmountable problem.

I've been googling for efficiency info on electrical motors to get a
handle on the likely energy dissipation in the motor(s) and the
indications suggest an efficiency of 95% or better for motors in the
100BHP and above range. This suggests some 20 odd KW would be
dissipated within the motor for the full duration of the braking time
(3.2 seconds).

In the case of an AWD setup, this splits the dissipation across 4
motors. since a typical braking balance between the front and back
'axles' would be in the region of 60/40, the dissipation in each motor
on the front axle will approximate to 6KW whilst those on the rear
axle will be 4KW.

Assuming equal power ratings for all four motors, this crude
calculation will under-estimate the front axle motors and
over-estimate the rear axle motors dissipation figures. More probably
the front hub motors will be dissipating 7.5KW each whilst the rear
hub motors will be dissipating 2.5KW each.

That 7.5KW over a 3.2 second period corresponds to a temperature rise
of 62 degrees C for a Kilogram's worth of copper in the motor
windings. The more copper the lower the temperature rise and vice
versa for less copper. I've no idea on how much copper by weight such
a hub motor might have but a guess at somewhere around 1 or 2
kilograms seems a plausible amount so it looks like the motors should
cope ok.

--
Regards, J B Good

On 29/04/2014 03:10, Johny B Good wrote:
On Mon, 28 Apr 2014 12:52:18 +0100, Clive George
wrote:

On 28/04/2014 10:42, Dave Plowman (News) wrote:
In article ,
Johny B Good wrote:
On Sun, 27 Apr 2014 23:51:47 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
What you're overlooking is the fact the 'generator' mode load current
will be well within the normal peak running current specificied for
its use as a motor.

What you're suggestion is peak retardation will be on a par with peak
acceleration. Nonsense.

If we're talking about a family car with comparable acceleration
performance to that of a mid specced ICE powered car, then peak
acceleration will be limited by tyre grip, say a tad over 1G. The same
tyre grip consideration applies on deceleration so the same peak motor
current limit applies.

There is no family car ever built where it will break traction through
engine torque. But even the most basic is capable of doing that by hard
braking if it doesn't have ABS, etc.

To get *any* car which will accelerate as fast as it brakes means going
for some very exotic machinery indeed.

Electric motor not 'exotic' enough then?


JBG and TNP have missed the difference between force and power. It

I haven't missed that distinction.

doesn't take much power to break traction from stationary, but the
amount required goes up as you get faster.

Torque output from a motor very closely approximates the current draw
which is the limiting factor when it comes to I squared R losses and
peak power output is determined by the maximum rpm limitation which
also approximates to the applied voltage. Similar limitations also
apply when the motor is acting as a generator in a KER system.

Irrelevant.

Similarly the amount of power you need to dissipate in a brake goes up
as you get faster. To slow a 1.5 tonne car at 70mph at 1G requires you
to dissipate 460KW or 620 HP. If your windings aren't built to provide
that kind of input power, they're not going to cope with shoving it back
out again.

Assuming the direct drive motor is designed to cope with sustained
maximum cruising speeds and capable of providing an initial 1G
acceleration, it will be guaranteed to cope with deceleration
stresses.

No. That's you making the same mistake you denied making earlier. It
needs to be able to provide the 1G deceleration at that maximum cruising
speed (and indeed all speeds), which is a whole lot harder than the
initial one or that required to maintain a maximum cruising speed.

Your figures looked to be 'about right' initially but I thought it
best to calculate the peak horse power for myself and it turns out to
be a more modest 566.7 BHP. You've over estimated it by nearly 10%
(discrepency is actually 9.4% greater).

Show me your sums. I rounded G to 10, used 750W/Hp rather than 745.7,
1600m per mile rather than 1609.344, but otherwise my numbers are
accurate. Here are some slightly tweaked ones :

a = 9.81 ms-2. Mass = 1500Kg. f = ma, force = 14715N.
Speed = 70mph = 31.3 ms-1. Power = force * speed = 460473.6W = 617 Hp.

This isn't a large error but it does suggest you're trying to big up
the problem of high transient power delivery rate to better favour
your argument.

No, it suggests you're not doing your sums right. It's not hard to do,
but seeing as you're challenging mine you'd better make properly sure
that yours are correct.

Assuming a constant deceleration of 1G, it will take 3.2 seconds to
come to a standstill. The motor winding current will be constant
whilst the voltage output falls linearly with reduction in speed. The
I squared R motor winding losses will therefore be essentially
constant over the deceleration period (3.2 seconds) whilst the average
power output will be half the peak (283 BHP).

Translating into watts we get 211.4 KW and into joules we get 676.44
Kj during the 3.2 seconds worth of braking to a standstill which is
enough energy to bring 2 litres of water to the boil from a starting
temperature of 20deg C.

Sanity check your numbers - you've got a conversion problem somewhere.
You should be getting 1/2 m v2, and you're not - 0.5*1500*31.3*31.3 = 734kJ.

The main issue in contention is the torque stress induced I squared R
losses in the motor windings. Handling the recovered energy is a
seperate but not insurmountable problem.

It's the problem Dave and I have been talking about. 450+KW is a non
trivial amount of power to sink.

I've been googling for efficiency info on electrical motors to get a
handle on the likely energy dissipation in the motor(s) and the
indications suggest an efficiency of 95% or better for motors in the
100BHP and above range. This suggests some 20 odd KW would be
dissipated within the motor for the full duration of the braking time
(3.2 seconds).

In the case of an AWD setup, this splits the dissipation across 4
motors. since a typical braking balance between the front and back
'axles' would be in the region of 60/40, the dissipation in each motor
on the front axle will approximate to 6KW whilst those on the rear
axle will be 4KW.

Assuming equal power ratings for all four motors, this crude
calculation will under-estimate the front axle motors and
over-estimate the rear axle motors dissipation figures. More probably
the front hub motors will be dissipating 7.5KW each whilst the rear
hub motors will be dissipating 2.5KW each.

That 7.5KW over a 3.2 second period corresponds to a temperature rise
of 62 degrees C for a Kilogram's worth of copper in the motor
windings. The more copper the lower the temperature rise and vice
versa for less copper. I've no idea on how much copper by weight such
a hub motor might have but a guess at somewhere around 1 or 2
kilograms seems a plausible amount so it looks like the motors should
cope ok.

Now do it from 100mph. Or even 130mph - that's a pretty common top speed
for a big family car these days. (and they come with bigger vented disks
than TNP remembers).

With that time doubled, you're up to 120 degrees extra in the copper in
a single stop. Those motors are going to die, and you still haven't
addressed the problem of shifting half a megawatt elsewhere.

Now there's no reason to not use the motors as regenerative brakes -
that in itself is sensible. The problem comes when you try and use them
to completely replace the conventional friction brakes. They can't - big
lumps of iron can take a lot more abuse than copper windings.

In article , Dave Plowman (News)
scribeth thus
In article ,
tony sayer wrote:
Well exactly. Train brakes are pretty crap by and large.

Due to the actual brake system or the steel wheel on steel rails?...

It's not that long ago they had simple brake blocks. Then they got discs -
long after they were common on cars.


Yes, but back to the original question its not much use being able to
stop the wheel from rotating unless it maintains grip with the rail.

And seeing the vids on Youtube of some poor olde kettles slipping to get
trains up some grades;!...
--
Tony Sayer

Now do it from 100mph. Or even 130mph - that's a pretty common top speed
for a big family car these days. (and they come with bigger vented disks
than TNP remembers).

Yes I suppose it is, but are any electrically powered cars those likely
to be a round for some time to come powered by chemically stored leccy
going to be doing those speeds .. that often;?..

I'm buggered if I can afford to wind my A6 up to those speeds assuming I
could find a bit of the M11 or A14 clear enough and could afford the
petrol;!..



With that time doubled, you're up to 120 degrees extra in the copper in
a single stop. Those motors are going to die, and you still haven't
addressed the problem of shifting half a megawatt elsewhere.

Yes a substantial amount of power but like lightning, hardly enough to
run a 100 watt light bulb for any real amount of time but all at once it
can do nastiness;!.

But anything on how long it would need to sustain that amount of power
dissipated in the heat rise of the windings, and the means of power
dissipation connected to same. After all its going be a while before
you'll get the car wound up to those high speeds again?. And assuming
electric breaking does come about no doubt they'll be some clever
software preventing you from doing that too often;?.

Let alone reporting your road speed directly to uncle Bill who will get
his 'puters to send out the necessary speeding tickets delivered by
electronic means to your mobbie, or the wrong sort of "points" in your
software to prevent you doing that again;!(..


Now there's no reason to not use the motors as regenerative brakes -
that in itself is sensible. The problem comes when you try and use them
to completely replace the conventional friction brakes. They can't - big
lumps of iron can take a lot more abuse than copper windings.

Iron might but brake pads?..

Has anyone done any research into this very subject for conventional
road going vehicles?.

And seeing the storage limitations I'd hardly think you'll be able to
throw that sort of power away as heat.

If anyone has got one of these new fangled motor devices how do you get
on with heating same, shirly not as much insulation wrapped around the
car as harry has round his manor house;?..
--
Tony Sayer

On Tuesday, April 29, 2014 9:07:27 AM UTC+1, tony sayer wrote:
In article 53ffa83444dave, Dave Plowman (News)
dave scribeth thus
In article ,
tony sayer wrote:

Well exactly. Train brakes are pretty crap by and large.

Due to the actual brake system or the steel wheel on steel rails?...

It's not that long ago they had simple brake blocks. Then they got discs -
long after they were common on cars.

Yes, but back to the original question its not much use being able to
stop the wheel from rotating unless it maintains grip with the rail.
And seeing the vids on Youtube of some poor olde kettles slipping to get
trains up some grades;!...

So many folk imagining that train braking is all done by wheel to track friction. Its not.


NT

In article ,
Johny B Good wrote:
To get *any* car which will accelerate as fast as it brakes means
going for some very exotic machinery indeed.

Electric motor not 'exotic' enough then?

You think a Prius exotic? Say no more. ;-)

--
*HOW DO THEY GET DEER TO CROSS THE ROAD ONLY AT THOSE YELLOW ROAD SIGNS?

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
wrote:
Yes, but back to the original question its not much use being able to
stop the wheel from rotating unless it maintains grip with the rail.
And seeing the vids on Youtube of some poor olde kettles slipping to
get trains up some grades;!...

So many folk imagining that train braking is all done by wheel to track
friction. Its not.

Care to expand on that?

--
*I'm not as think as you drunk I am.

Dave Plowman London SW
To e-mail, change noise into sound.

On 29/04/2014 10:32, wrote:
On Tuesday, April 29, 2014 9:07:27 AM UTC+1, tony sayer wrote:
Yes, but back to the original question its not much use being able to
stop the wheel from rotating unless it maintains grip with the rail.
And seeing the vids on Youtube of some poor olde kettles slipping to get
trains up some grades;!...

So many folk imagining that train braking is all done by wheel to track friction. Its not.


Apart from the fact it should correctly be called adhesion, I'd like to
see another method you could use. Airbrakes, anyone? (Not normal brakes
operated by air, but large movable plates offering air resistance). Or
maybe using eddy currents in a plate attached between the rails?

Trams used to have large electromagnets fitted under the bogie frames
almost touching the rails to increase the force between the wheels and
the track, but it was still all done by the adhesion between the steel
wheel and the steel rail. On the Paris Metro, it's all done by the
friction of rubber tyres on concrete which can give some quite fearsome
rates of acceleration and deceleration.


--
Tciao for Now!

John.