RE: [Fwd: [Fwd: 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>

Hi Matt,

I'm glad to see you think Tesla was good at something.

>If a theory gives the correct answer EVERY time it is used, that's good
evidence that it's pretty at least close to correct.

Let's see if you still believe this at the end of this message.

>It was a diary and was not intended as a reference book.

Regardless of the reason CSN was written, it is a good reference book.  It
is not a book on physics principles, though, it is a reference book of
innovative ideas based on hard data.  I'll bet many of the readers of this
list own this book just for this reason.

>His experiments were straightforward and readily duplicated.  The effects
you report are not.

The effects I reported?  I must have missed that, what effects did I report?
I posted an article on Tesla's discovery that capacitance and inductance are
variable.  His work supports his proclamation.  It's pretty straightforward.
Why are you shifting blame to me?  What if I showed you the effects you
report are wrong?

>What to learn and how to go about learning it?  Explain.  Might be fun to
try.

Looks like your going to learn something about the effect of temperature on
a coil in a minute.

>> What's so wrong about admitting that a Tesla secondary coil's inductance
has
>> minute variations in inductance over time?  Does that imply the entire
>> knowledge base of physics will fall apart or something?

>No one doubts that the inductance change by minute amounts due to
temperature expansion and other mechanical effects.

_I_ doubt it.  Where do you get this information from?  Take a coil from
your shelf and connect it to your best LCR meter.  Note the inductance.
Then apply a hair dryer to the coil and raise the temperature of the
windings 50 degrees or 100 degrees.  100 degrees should account for average
temperature change at your house in one day if you live in some strange
climate.

I did this experiment.  The coil measured 4.57 mH when I started and it
measured 4.57 mH after I heated the coil with the highest setting of the
1875 watt hair dryer for 5 minutes.  The windings got quite hot, but there
was no stable change in inductance.  There were a few nanohenries inductance
while the temperature was changing and this was likely due to a
thermoelectric effect that induces a current between materials of different
temperatures.  I hear all this talk about temperature affecting the
inductance of a Tesla coil and accounting for variations in measurements.
Why doesn't my coil respond to temperature like yours and everybody else's?
Even the strong air flow from the hair dryer didn't affect the inductance.

But when I took an NIB magnet and moved it up and down the outside and away
from the coil, the inductance changed by up to .2 mH.  A flowing magnetic
field affects my inductance in a meaningful way, but not temperature.  I
suspect you are the victim of a great deception.

When I wound this coil I was in Vermont.  And as I usually do, I tested the
coil over a period of several days until the inductance was stable and then
wrote it on the bottom of the coil.  In Vermont in 1997 this coil measured
4.54 mH.  Today this same coil in Illinois measures 4.57 mH.  I just proved
that temperature doesn't cause this wide of a swing in inductance, at least
not in this coil.  There must be other factors involved.

I have a combination flat spiral / solenoid coil arrangement that varies as
much as 25mH in one second.  The meter never stays still.  Some times the
variation for this coil is just 3mH per second.  Not only is there variation
in this coil, but the amount of variation also varies.  This certainly is
not due to temperature or humidity changes, wouldn't you agree?  I have done
several tests on this coil to see what was causing this wide variation in
inductance.  I found that most of this inductance change is due to my house
wiring.  When I turn off all the power to my house, the inductance reading
stabilizes.  But over longer periods of time, it still changes.  Certain
coil combinations are particularly sensitive to magnetic fluxuations.

>Depending on the coil form and the winding geometry, changes can be a
fraction of a percent for large temperature changes.

"Fraction" is too generous.  Infinitesimal would be a better word.  My
coil's inductance changed .007% from Vermont to Illinois.  That was
measurable.  The change you are looking for due to temperature is much
weaker, if at all.  And that's from an extreme temperature change.  There
was at most a 20 degree temperature change in the room temperatures at the
times I measured this coil.  Temperature most certainly is not a significant
cause of inductance variation in a coil.  It is among the weakest factors
contributing to variable induction.  Everybody on this list with a coil, LCR
meter and hair dryer can prove this for themselves.

>What we reject outright is the thought that sunlight or moonshine or gamma
rays or whatever change the inductance.  An exception to that would be if
there were enough energy absorbed to change the temperature and hence the
coil dimensions.

Temperature has little to nothing to do with it.  That's a myth and it
should be laid to rest soon.

Tesla said he doubted moonlight had anything to do with it.  He noted that
direct sunlight affected his capacitance measurements.  He also noted the
coil's relative position with the earth, moon, and sun seemed to affect
inductance.  All of these bodies are constantly moving relative to each
other and each of them has a magnetic field.  Naturally the earth's magnetic
field is the strongest (and perhaps explains why Wheeler's formula is
empirically based and has lower values than the classic inductance formula.)
The movement of the coil relative to the sun and moon could explain
variations in inductance if the magnetic fields are cutting the coil.  There
is at least sound scientific basis for this idea, as opposed to temperature
effects.

The sun and moon are not the only magnetic forces that can affect a coil
though.  I have found that my house wiring in the walls and ceiling
significantly affects certain arrangements of coils.  There are also natural
variations in the earth's magnetic field.  Some are related to inner earth
geology, some are related to geomagnetic storms, others may be related to
flowing mineral water under ground.  The electric currents flowing through
the earth, both natural and manmade, likely cause magnetic currents that
affect coils.

I'll be subjecting my coils to intense humidity in the shower soon to see
the exact effects of humidity in a controlled environment.  I suspect that
data associated with outdoor temperature and humidity changes are
misperceptions of the real events altering inductance.  When storms pass by,
they are associated with changes in the electric currents in the earth and
atmosphere.  We need to get to the bottom of this and determine conclusively
which forces exactly affect inductance.

Dave