ultracapacitors

[Martin Jackson <mjackson@vcn.bc.ca>]

  Peter VanDerWal on ultracapacitors in AC drives

"I didn't say that they can't hold a charge for a long time, I said they
aren't EFFICIENT at holding a charge long term (from what I understand)."

  Right, but it doesn't leak down that fast.

>  Getting the power out is not hard. Getting the sensible regen
>  with climbing Cap voltage and declining motor voltage is the toughy.
>  But, the energy from one good stop is the perfect minimum charge.

".......I said that getting power out in an EV application was tough.  
If you have come up with a way to get the power out in a useful manner in 
an EV please share it with the list."

  I thought that was covered

"Because the voltage drops so quickly you can't just parallel the pack.
Putting the UC's in series with the pack is a possibility, however it
has a few problems.  As I see it; you'll need a controller that I don't
think exists yet.  One that can do regen (and somehow store the energy in
UCs instead of the pack) AND that is rated way above pack voltage AND can
handle a very wide range of input voltages.   Plus you'll need the
contactors to switch the UCs in and out of series.  Plus you'll need a whole
bunch of those very expensive UCs"

  Since we are talking blue sky here, I think we should speculate that
  series switching and the controller are not major problems. Regen isn't 
  in my scheme in the short term because I haven't heard how to do it. As 
  to expensive, these are very expensive now, but it should be reasonable 
  to produce a unit for a 'reasonable' amount in production. And 
  production can be driven by the E power industry for power factor 
  correction.

"Seems to me that it would be simpler, more efficient and MUCH cheaper
just to buy a regen controller and store the energy in the pack."

  Sounds right to me. Today

    "UCs are neat, but so are blue LEDs.  Just because it's a neat 
technology doesn't mean there has to be a way to use it in an EV."
    
  I think this is a weird viewpoint. Anything that will reduce the 
  Peukert losses and Cheaply boost acceleration is worth trying. As to 
  blue LEDs, I just got an inexpensive color portable, and the 480,000 
  blue dots are neat. Nicer than the green ones. 
    
    "As I've said before, I don't think UCs are ready for use in an EV yet.
However; if someone out there has a whole bunch of money and wants to prove
me wrong, please post the results :-)"

  I wish they were ready.
  
  LEE HART on ultracapacitors in AC drives:

"Ultracapacitors can hold a charge for months. But unlike a battery, the 
voltage falls exponentially with time. So it falls the fastest when it is 
the most charged. If it can hold a charge for 6 months, then after 3 
months you only have 10% of your energy left."

  Putting this into perspective, the loss in charge over 1 hour is small, 
  so the leakage is minor in terms of energy. So an acceleration boost is
  available for the time you're driving. And I suspect even the next day,
  the UC would still get you out of your driveway.

"Capacitor efficiency is nearly 100% for very short periods of time 
(seconds), but gets rapidly worse as time increases. It will be worse 
than batteries once you get past a minute or so."

  This is true by definition (perhaps for part of an hour rather than a 
  minute). Note that the UC is proposed as a start battery replacement 
  and a Catalytic converter prewarm power supply, but not for lights and 
  ignition.

  Peter again:

> *** I don't quite get it - I thought charge was energy, so if the
>UC loses its charge rapidly, it can't be rated to hold charge for very
>long periods. Unless the UC was holding a much-lower-than-rated voltage
>charge for a long time, right from the beginning. In which case, wouldn't
>the rating be wrong? ***

    "It INITIALLY loses it's charge rapidly (though how fast is rapid? it's
all relative)."

    Right
    
    "Let's use the old water analogy....."

  The hole is smaller than this.

    "Just because they hold a lot of energy doesn't mean that they are
particularly good at holding it or that they have a low ESR or even that
they can be charge/discharge very quickly."

  As stated earlier, the discharge rate is very fast and allows a lot of 
  Power/cu.ft.  They don't hold a lot of Energy; Range (energy) might be 
  two blocks on a UC alone. Quickly (power).
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