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Re: [carfree_cities] Re: Rail & Rubber

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  • J.H. Crawford
    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
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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 context of your reply.

      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
      >
      >
      >Sadly, this link doesn't work for me? :(

      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
    • Tony Brewer
      ... 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
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        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
      • Todd Edelman
        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
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          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
          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
          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






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        • J.H. Crawford
          ... 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
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            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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