RE: Variable Capacitance and Inductance

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Thanks for sharing that Bart.

I think it is interesting, regardless if the most noticeable factor
affecting a change of capacitance in humidity or a gamma ray burst, that the
amount of charge a capacitor can hold can change.  In a large sphere
capacitor, the dielectric is air.  It seems easy to see how barometric
pressure, humidity, and temperature can affect the dielectric in this case.

I assume your "main" cap is your primary cap and that it has either an oil
or mica dielectric?  How would humidity affect the dielectric of your
capacitor such that the capacity would change 6% in two days?  I wonder if
Tesla's salt water capacitors had anything to do with his 50% variation of
capacitance in a building?

As a quick test, I took two .02uF mica capacitors (both rated for 2000V) and
put them in series.  When measuring the capacitance with my BK Precision
875A LCR meter the inductance was exactly .010uF.  I then got out a hair
dryer and applied heat directly to the capacitors for 10 minutes.  The
capacitors got quite hot to the touch, but the capacitance did not budge.
The reading was still .010uF.  I then put the capacitors and meter in my
shower and let the water run continuously for 10 minutes.  The capacitance
still measured .010uF.  For the capacitor I used in this quick experiment, I
saw no effect from temperature or humidity.  I'll try this with other types
of capacitors and see what I get.

Dave


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, May 23, 2002 9:48 PM
To: tesla-at-pupman-dot-com
Subject: Re: Variable Capacitance and Inductance


Original poster: "Barton B. Anderson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Jan, Dave,

Regarding the box experiment. If the cap is in a sealed box, it is still
susceptible to temp
variations of the boxes surroundings. The capacitance "will" change as the
box is exposed to
various locations. I suspect temperature and humidity are the key players
for these changes in
capacitance. Recently I've taken measurements of my main cap, and the main
cap has changed by a
factor of ~4nF. What was measured at 61nF grew to 65nF (same meter and
leads) taken one day
following a 2 day cycle of rain (it's possible the meter is the one
affected?). Possibly premature,
but I feel the increase in humidity has affected the cap by way of the
objects around it, and those
objects were affected by the rain and temp. Unfortunately, I didn't see the
capacitance change
coming and therefore didn't log humidity or temp data to coincide.

Take care,
Bart

Tesla list wrote:

> Original poster: "David Thomson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
>
> Hi Jan,
>
> >Yes, L and C do vary, if the surroundings of the place of measurement are
> changed. If the surroundings remain absolutely fixed, exactly, L and C
won't
> change.
>
> Thanks.  That's the point right there.  Inductance and capacitance are
> affected by stellar activity, geomagnetic activity, house wiring, and the
> abundance of metal in our society and even in the ground.  Atmospheric
> conditions will affect the electrostatics of a coil and capacitor, but
there
> are many influences that affect inductance and capacitance.
>
> The observations of Tesla and others on this list of variable inductance
in
> there coils is not necessarily the result of faulty equipment, measuring
> techniques, or humidity.  It has taken a while to get to this point, but I
> think we may be there.
>
> When the environmental factors contributing to variable inductance and
> capacity are acknowledged then that opens the doors to further knowledge
in
> our art of coiling.  There are certain designs of coils that are more
> susceptible to environmental changes than others.  The combination flat
> spiral and secondary coil that I use produces a fluctuation in inductance
> readings between 5mH and 30mH each second when my house power is on.  Even
> this fluctuation varies over time.  When I measure the inductance of a ver
y
> large flat spiral coil, the inductance meter won't work.  These
observations
> are not equipment malfunctions but measurements of real phenomenon that
are
> worthy of further study by coilers.
>
> Based on the limited data I have collected so far, house current appears
to
> be the most influential factor that alters inductance and capacitance in a
> dwelling.  When my combination coil is operating I see fluctuations in its
> functioning as well.
>
> >Here's an experiment for your (maybe for others too!):
>
> This is a good suggestion.  I have also planned a similar experiment where
a
> capacitor and inductor would be stored in evacuated jars and measured for
a
> period of time.  This would eliminate the humidity and temperature
factors.
>
> Dave