wrote:
On Jan 1, 1:24Â*pm, wrote:
wrote:

http://nextbigfuture.com/2009/12/sup...enable-electri...

--
Mark

Practical, manufacturable high temperature superconductors would enable
a whole bunch of neat things and would be as spectacular as a cure for the
common cold, lasting peace in the Middle East, and controlled fusion, and
is just as likely to happen in the near future.

I recently read up on some work being done with graphene
supercapacitors. I IRC, it was at Caltech. What was interesting is how
they performed at lower temperatures (e.g. room temp.). Also, charging
times were impressive. Still in the realm of research, so it wasn't
clear to me how well it would scale beyond smaller applications
(consumer electronics, for example.


Supercapacitors are great for things like keeping your clock from flashing
on every minor power failure, but not that great for real power application.

The basic physics of capacitors says the energy density can never be as
good as existing batteries. Graphene makes them better but it will take
yet to be invented materials to match batteries.

Capacitors are also a poor choice for running something like a motor because
of their discharge curve.

While a battery's discharge curve is basically flat until it gets close to
full discharge, then takes a big dive, a capacitor discharge curve is a
straight line between fully charged and zero.

Motors operate over a narrow voltage range. Electric motor speed control
is done by pulsing the motor voltage on and off, not by varying a constant
voltage.

Now it is possible to build a thing that will take in a lower voltage and
output some constant higher voltage to keep a motor happy.

The problem with that is it is more complexity subject to failure, not
good with airplanes, and it would require big, heavy, high current
transformers, which ups the weight a good bit.

My wild assed guess is that if electric airplanes ever become practical
without Star Trek technology, it will likely be through a fuel cell that
is yet to be invented.