Re: Variable Capacitance and Inductance

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

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

Hi Dave,
Hopefully you saw my other post with the transformer connection causing the
variation. It just
happened to fall within the time frame of this topic and the associated
weather. Although it
pointed that way, it wasn't (I was a bit hasty in commenting and should
have made planned checks
before doing so). My mind hasn't changed about C or L changes with temp and
humidity. Conductors
expand/retract with temp and porous materials become more conductive with
humidity. Obviously, a
wound coil will exhibit changes far more than a sphere or sealed cap just
based on it's geometry
and exposure. The change on a sphere might be so small that it can probably
be ignored 99.9% of the
time and is probably difficult to measure.

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>
>
> 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