## Re: [carfree_cities] Re: Rail & Rubber

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• A reminder to everyone: PLEASE trim the junk off your posts-- those parts of the posts to which you are responding that are not necessary to understanding the
Message 1 of 29 , Jun 1, 2005
those parts of the posts to which you are responding that are

Thanks

Now....

>> I think so. This means that street running installations
>> should have a shed-like building; see:
>>
>> http://www.carfree.com/papers/05vld05452.jpg
>
>

Oh, sorry. I THOUGHT I had checked it. I forgot to post it.
It IS now at:

http://www.carfree.com/papers/05vld05452.jpg

>> about the length of the tram (say 150 feet). As mentioned
>> in the short-wire proposal, this is enough distance that
>> braking and acceleration energy can be managed through the
>> overhead wire as long as there are pickups at both ends of
>> the vehicle.

>Interesting idea, using line power to "bolt" the vehicle along. At 3
>m/s^2 (a value easily reached via electric drive, and proven to be
>human comfortable through zillions of street cars)

No. The PCC cars from the 1930s had the highest acceleration
I know of, about 2.2 m/sec2. Many modern cars cannot achieve
anything above 0.8 m/sec2. The PCC values were chosen after
extensive human-factors engineering tests and cannot, I think,
be safely exceeded.

>you should be able
>to reach 27 meters per second (62 miles per hour) in less than 90
>meters, or, 300 feet. (Assuming of course I did the math right.)

I assumed 50 km/hr at 0.2 G, which requires 50 meters to reach
running speed. I believe that anything above 50 km/hr is unsafe
and too noisy for street running, but it is common practice to
run considerably faster than this.

>> Now, there's a problem. Literature on these ultra-capacitors
>> mentions that they have achieved their incredible energy
>> density by allowing the internal resistance to be considerably
>> higher than normal. This is a warning flag for me. When dealing
>> with batteries, internal resistance is a limiting condition on
>> cell efficiency--the higher the resistance, the higher the
>> losses. I strongly suspect that the same holds true for caps.
>
>Er?
>
>As I understand it, it is exactly the opposite.

Let's have a report from an EE who really knows. I believe
that increased internal resistance always results in increased
losses. Certainly, the capacity manufacturers were reluctant
to go to higher resistance but felt forced to due to energy
density concerns.

>A battery stores electricity via chemical reactions, and thus wants
>LOW resistance so the reaction can proceed unhimdered.

wants low resistance to minimize losses to heat in the cell

Regards,

------ ### -----
J.H. Crawford Carfree Cities
mailbox@... http://www.carfree.com
• ... The relevant formulae are: Pc = 1 /(1+2RC/t) Pd = 1-2RC/t where Pc is charging efficiency Pd is discharging efficiency (always less than Pc) R is internal
Message 2 of 29 , Jun 1, 2005
J.H. Crawford wrote:
> ...
> Now, there's a problem. Literature on these ultra-capacitors
> mentions that they have achieved their incredible energy
> density by allowing the internal resistance to be considerably
> higher than normal. This is a warning flag for me. When dealing
> with batteries, internal resistance is a limiting condition on
> cell efficiency--the higher the resistance, the higher the
> losses. I strongly suspect that the same holds true for caps.
>
> Is there an EE on the list who can:
>
> find the specs (not the handwaving Mitrac literature)
> do the math on net efficiency
> report back
>
> If the efficiency is not pretty high, this system does not
> work as we intend (although it may still have its uses).
> ...

The relevant formulae are:

Pc = 1 /(1+2RC/t)
Pd = 1-2RC/t

where

Pc is charging efficiency
Pd is discharging efficiency (always less than Pc)
R is internal resistance
C is capacitance
t is full charge or discharge time at a constant current

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

The value of RC for ultracapacitors meant for vehicular use is 2 Ohm-Farads
typically. Consider three examples where the total stored energy can provide
the maximum required power for 30, 45 and 60 seconds:

t = 30, RC = 2, Pc = 88.2%, Pd = 86.7%
t = 45, RC = 2, Pc = 91.8%, Pd = 91.1%
t = 60, RC = 2, Pc = 93.8%, Pd = 93.3%

Note that is the ratio (RC/t) that determines efficiency. R and C are
intrinsic to the type of ultracapacitor, but t can be anything. Lowering the
power or increasing the size of the capacitor bank will both increase t and
hence increase efficiency.

The efficiency during accelerating or braking will be more than the above
figures because full power is not needed all the time. The efficiency when
accelerating a tram or train from 0-30 mph is likely to be 90% for t = 30
and 95% for t = 60.

Full power for 30 seconds might not seem like much, but it would be more
than enough if stations are closely spaced and the terrain is not too hilly.

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

I think this proves that ultracapacitors can be very efficient.

Tony Brewer
• Hi, Related to this discussion of the supercapacitor-tram, it would not be a possible scheme for shorter distance regional trains (typical European railbuses
Message 3 of 29 , Jun 3, 2005
Hi,

Related to this discussion of the supercapacitor-tram,
it would not be a possible scheme for shorter distance
regional trains (typical European "railbuses" )
running on non-electrifried corridors as station
distances would be too great, right? From 2 to 5km, I
think.

Or would this be solved in a hybrid, where an engine
of some sort would take over as necessary?

----

Also related: For "On the Train to the Future!"
project I am proposing a reconstructed railbus which
which would also be "distributed sources": local and
renewable things like individual windmills, biogas
from waste or factories, etc. It could be done in
conjunction with European Commission DG Research
funded programme "EU Deep" www.eu-deep.com (one of the
partners also makes the engines for a railbus renewal
scheme here in Czechia,so MAYBE I am "half way
there"!!)

If anyone can look at the summary of the proposal, let
me know off-list. I might have to send it as an
attachment.

Todd, Prague

___________________________________________________________
How much free photo storage do you get? Store your holiday
• ... I wouldn t necessarily rule out the use of capacitors for these uses. Development seems to be on-going, and the biggest shot of energy needed is to
Message 4 of 29 , Jun 3, 2005
Todd said:

>Related to this discussion of the supercapacitor-tram,
>it would not be a possible scheme for shorter distance
>regional trains (typical European "railbuses" )
>running on non-electrifried corridors as station
>distances would be too great, right? From 2 to 5km, I
>think.
>
>Or would this be solved in a hybrid, where an engine
>of some sort would take over as necessary?

I wouldn't necessarily rule out the use of capacitors
for these uses. Development seems to be on-going, and
the biggest shot of energy needed is to accelerate
the vehicle out of the station and up to cruising
speed. Maintaining the speed of a train doesn't take
very much energy (due, of course, to its high efficiency!),
and the capacitors are most efficient when the loads are
light. So, I think it could be feasible for local train
service as well.

Regards,

------ ### -----
J.H. Crawford Carfree Cities
mailbox@... http://www.carfree.com
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