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Re: [Fwd: [Fwd: Re: Variable Capacitance and Inductance]]
Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>
> Original poster: "David Thomson by way of Terry Fritz
> 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
Indeed. to _experimental_ procedure 100 years ago.
Much has been learned since then.
> It is not a book on physics principles, though, it is a reference
> book of innovative ideas based on hard data.
I suggest it is a book of observations, together with
best guesses as to their meanings. Some such guesses
have proven out.
>>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'm guessing the reference is to Your report of
> I posted an article on Tesla's discovery that capacitance and
> inductance are variable. His work supports his proclamation.
His observations how a variation. I suggest that the
interpretation of that observation, as of any observation
is subject to discussion and verification. All
verification since then finds the 'capacitance increases
as 'plate' (ball) is raided does not occur.
> It's pretty straightforward.
The observations may be. Interpretation can be tricky.
> Why are you shifting blame to me?
I suggest this is a technical discussion 'blame'
is not generally a factor in such discussions.
> What if I showed you the effects you report are wrong?
Several suggestions have been made to do the measurement.
It is routine in science and engineering to discuss
(question) measurements and interpretations.
>>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
>>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
> 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.
Indicates it was a well built, mechanically stable coil.
> 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.
What two materials?
Thermoelectric effects only apply to CONDUCTORS.
Hint II: I have been dealing with thermoelectric effects,
off and on, for 50 years.
> 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?
One would need to list out the construction details
of 'eveybody's' to find out.
> Even the strong air flow from the hair dryer didn't affect
> the inductance.
Air flow, as such, has no known influence.
> 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.
Also: check manufacturers spec on accuracy of meter.
0.2mH may be on the edge of its accuracy spec.
(This illustrates my comment of some days ago:
the 0.2 mH may be outside the spec, but still
indicates that SOMEthing is going on. May or may
not be 'inductance change'.)
> A flowing magnetic field affects my inductance in a meaningful
Try the same with a random piece of steel, similar in
Try the same with a random piece of copper, similar in
size. (non ferrous, tin, whatever...).
Try the same using a nonconducting (wood, plastic)
pole in place of the hand.
Think about a metal detector. Think about how they work.
(they work in a variety of ways....)
> but not temperature. I suspect you are the victim of a great
Perhaps. Perhaps the stray capacity of the hand, or
the magnet is causing a change that the meter _reports_
as an inductive change. (The meter, basically, trusts
the operator to only present an inductance (perhaps with
> 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.
On the same meter?
Meters have tolerances.
> Today this same coil in Illinois measures 4.57 mH.
On the same meter?
Meters have tolerances.
When was the meter calibrated last?
(In a professional lab, all equipment used to make
serious measurements gets regularly calibrated. The
manufacture will supply a recommended interval. 90
days to one year might be apropos for such a meter,
that's a guess.)
> I just proved that temperature doesn't cause this wide of a swing
> in inductance, at least not in this coil.
Tend to agree.
(Thruout this thread, lack of specifics has been in
evidence. Eg which coil, when, how built. Tesla built
coils on wood frames, subject to variation in temperature
and humidity. (this is not an attack on Tesla, simply
an observation of fact.) A modern coil, on a PVC form,
sealed with modern sealants is quite stable, more stable
than would have been possible in 1900.)
> 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.
At a guess (and only a guess (and not an attack)),
Something else is changing.
the meter has an internal time constant that
is interacting with the two coupled coils
forming the test piece.
> 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?
Insufficent data, but tend to concur.
> 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
I suggest it is not the 'wiring' as such (since the _wiring_
is still present, but the stray fields from the wiring, or
from some appliance or other load. One might try switching
off one load at a time, etc. At a guess, the meter is
getting fooled by some stray field.
Move meter and test piece next to lights, while lights
> But over longer periods of time, it still changes. Certain
> coil combinations are particularly sensitive to magnetic fluxuations.
Or to something. cf above for some possible somethings.
> 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.
Which, except for the earth's field, is hugely smaller than
> 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.)
I would doubt that Earths field influences that. It, while
large, is tiny compared to other effects.
> The movement of the coil relative to the sun and moon could explain
> variations in inductance if the magnetic fields are cutting the coil.
They explain differences in _indicated_ _inductance_ IF
the indicator is fooled by the effects mentioned.
Earth's fields are subject to a HUGE amount of
investigation, for their effects on Geological prospecting,
Submarine detection, etc.)
> There is at least sound scientific basis for this idea, as opposed
> to temperature effects.
As noted, temperature effects will vary with details in
'coil moving thru field' (or field thru coil)
does not change the _inductance_. It induces a voltage
and or current. This is a function of inductance, but
does not change the _inductance_. cf any engineering
text. Since the usual inductance meter uses currents and
voltages, changes in stray fields can fool the meters.
> 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 suggest they may be detected by the coils. The inductance,
as opposed to the stay currents/voltages, does not change.
(this may seem like semantic nitpicking. 'tisn't. To
understand the meter reading, need to understand what it's
> 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 predict nil, especially for a well made coil.
Suggest checking the specs on the meter for its RH spec.
> I suspect that data associated with outdoor temperature and
> humidity changes are misperceptions of the real events altering
Or altering the indication...
by fooling the meter.
> 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.
1) May or may not be affecting inductance, exactly defined.
2) Most such changes are small enough to be negligible.
3) There are whole books writ on Atmospherical and
and earth currents, for pure physics, for weather, for
communications research. Citing the titles I have would
accomplish little, as they may not be available. And
general books can easily oversimplify.