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RE: Variable Capacitance and Inductance

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Dave,

At 06:42 PM 5/25/2002 -0500, you wrote:
>Hi Terry,
>>Maybe I missed something here since I don't know where inductance vs.
>temperature effects got started...
>Dave T.>>At least one person on this list has proposed to run a test over
>time to see if there were indeed a variation in inductance in a coil.
>Terry F.>>Done that ;-)
>>>Humidity (especially rain) seems to affect surrounding structures causing
>>great losses.  Temperature affects copper losses directly...

Oh! :o))  A short memory is a wonderful thing ;-))  Actually that test
shows Q and the coil's resonant frequency changing.  We think the Q may
have some to do with the variation in the copper's resistance with
temperature since indoor experiments tended to suggest that.  But not
totally sure without like a steel chamber to absolutely isolate the coil
from other effects.

>I was talking about a test for variation of inductance in a coil and you
>gave your link.  The most relevant chart on this link is titled "Frequency
>variation with temperature".  If this wasn't the chart that showed the
>variation in inductance, which one is it?

Resonant frequency here also depends on the capacitance (like Medhurst
capacitance) and the things that affect it which I "think" is the major
factor rather than changing inductance.  Sorry if I confused there.  I
probably don't have enough data to say too much for sure other than I
"think" things are what I think ;-))

Did you ever try a coil that was wet or maybe even underwater to see if
inductance would change?  That woudl be sort of interesting especially if
it did.  I'll search around here to see if I have a coil that can be soaked
too and try...

>Ed said: "No one doubts that the inductance change by minute amounts due to
>temperature expansion and other mechanical effects.
>>From Ed's statement, it doesn't take much to gather that variable inductance
>due to temperature is a well established scientific fact.

Jim was thinking of such effects as the torroid and coil expanding and
contracting and how that would affect the resonant frequency in the QVAR
test.  Not sure if he concluded anything there.

>For all the data you collected, and for your statement above that somebody
>(you and Paul) has already identified the causes of variable inductance,
>please tell me plain and simple; What is the cause you have identified
>(proven, discovered, whatever the correct term may be) for the variable
>inductance in a coil?

I think the inductance is stable but water in the woodwork and such is
affecting the capacitance of the secondary a little causing the variation
in frequency.  Paul can predict by computer that a lot of the Q variation
is due to copper resistance changing with temperature but surrounding
humidity in the house woodwork is having an effect too.  Rain on the roof
has a dramatic effect!!  Note that the variation is only 0.1%  What does
have us stumped is the q of f1 stays stable but f3 and especially f5 vary a
lot.  We don't know why...  We took the data, and at least I just sit and
stare at it...  I have not seen the light yet, but I am still staring...  I
must write up the details or the data will be just as sketchy as Tesla's...
 I can just hear them 100 years from now "Yep!, Terry and Paul sure took
some great data there but to bad we don't know what of..."  

A lot of detail is at: