Re: [carfree_cities] Re: Rail & Rubber
- 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 context of your reply.
>> I think so. This means that street running installationsOh, sorry. I THOUGHT I had checked it. I forgot to post it.
>> should have a shed-like building; see:
>Sadly, this link doesn't work for me? :(
It IS now at:
>> about the length of the tram (say 150 feet). As mentionedNo. The PCC cars from the 1930s had the highest acceleration
>> 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)
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 ableI assumed 50 km/hr at 0.2 G, which requires 50 meters to reach
>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.)
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-capacitorsLet's have a report from an EE who really knows. I believe
>> 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.
>As I understand it, it is exactly the opposite.
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
>A battery stores electricity via chemical reactions, and thus wantswants low resistance to minimize losses to heat in the cell
>LOW resistance so the reaction can proceed unhimdered.
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J.H. Crawford Carfree Cities
- J.H. Crawford wrote:
> ...The relevant formulae are:
> 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).
Pc = 1 /(1+2RC/t)
Pd = 1-2RC/t
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.
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
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
could be powered by one of various "alternative fuels"
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
If anyone can look at the summary of the proposal, let
me know off-list. I might have to send it as an
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- Todd said:
>Related to this discussion of the supercapacitor-tram,I wouldn't necessarily rule out the use of capacitors
>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
>Or would this be solved in a hybrid, where an engine
>of some sort would take over as necessary?
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.
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J.H. Crawford Carfree Cities