ONCE AGAIN (THIRD TIME) I AM SENDING THIS MESSAGE BECAUSE IT DID NOT
BOUNCE TO ME (AS TO A GROUP MEMBER). NOR DID I HAVE A MESSAGE FROM THE
POSTMASTER. SOMETHING IS WRONG, PROBABLY AT THE UNIVERSITY LEVEL. THEY
ARE FIXING SOMETHING. I APOLOGIZE FOR DELAYS OR REPETITIONS.
........................................................................
Yes John, I goofed. And I agree that a capacitor nominally 1 F can in
reality have C=1.2 F. Thanks for correcting me. This takes care of my
50 % of the "non-electric" energy concern.
I am in the same boat as you, I have no answers to the described properties
of these supercaps. But some phys-L-ers are very knowledgable and can help
us to understand the situation. Here are my questions:
a) Why are the discharging and charging curves non-exponential?
b) Why is the effective R*C associated with the magnitude of I?
b) What is this residual voltage coming from inside a cap disconnected
from a source after it was shorted for one or two seconds?
c) Which parameters are involved in the "hysteresis" and why?
As a physics teacher I am sensitive to all significant discrepancies
between what we teach and what happens in reality. It bothers me that a
unit called capacitor does not discharge exponentially through a resistor.
The factor of 2 or 3 in the effective R*C (if my supercap is not a fluke)
would very significant. I would like to understand this property, at least
superficially. When a cannon ball does not follow an idealized parabolic
trajectory I can say "air resistance", when an ordinary capacitor is self-
discharging I can say "a parallel leakage resistance". What should I say
to myself when a capacitor is recharing internally or when the rate at
which V is changing does not agree with what I teach?
In my opinion supercaps are suitable for student-based research; the
equipment needed to study them is available in most of our labs. We can
take advantage of their "unusual" properties to promote student's
interest. I hope this is not the end of the thread.