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Re: Wet Coils

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

Hi Dave,

At 10:13 PM 5/25/2002 -0500, you wrote:
>OK, that didn't take long.  I checked the same coil as last night, it read
>4.57mH before starting.  I placed the coil while connected to the LCR meter
>on the floor of the shower and turned on the water.  Some water droplets
>coated the outside of the coil.  After two minutes the inductance was still
>4.57mH.  So I wrapped a soaking wet towel around the coil and measured the
>inductance.  After a couple minutes the inductance did appear to increase
>just enough that the reading vacillated continuously between 4.57mH and
>4.58mH.  It did appear to change the inductance measurement somewhere
>between 10 to 90 nanohenries.  That's the best resolution I have at this
>range of inductance.
>Mind you, this is with a wet towel.  Not only is the humidity 100%, but
>there is a substantial mass of water in close proximity to the windings.
>Tomorrow I'll get a bucket and actually submerge the coil and see what
>results I get.

Cool!  So it appears that gross humidity does not appear to have any or
only a tiny affect on inductance.  I don't think this test has ever been
mentioned before.  I am sure the Q dropped like a rock but the inductance
held up.  "I" didn't think that would be the case.  Shows what I know ;o))

>>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
>Do you have an ion generator?  If so, put it next to the coil and see what
>you get.  If you don't, they sell them at All Electronics for less that $5
>each.  It's really a useful device to have on hand when working with some
>electrostatics projects.

I ran a 50kV power supply next to a coil once so that it would charge the
area near the coil, it had zero effect on the resonant frequency.  I used
very sensitive equipment that could detect less than 1Hz change.  The
resonant frequency was the same with the nearby area at zero volts above
ground or 50kV.

>>Paul can predict by computer that a lot of the Q variation is due to copper
>resistance changing with temperature
>Has this prediction been verified by manually heating the coil with
>something like a hair dryer?

It could be...  but not tonight ;-)

>>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.
>What exactly are the parameters of f1, f3, and f5?  I wondered that when
>looking at the graphs.  You wanted someone to peer review your project, I'm
>interested in fully understanding your results.

F1 is the fundamental frequency, F2 is the third harmonic and f5 is the
fifth.  As you resonant the coil you hit all those resonances.

I just remembered Paul has the page at:


>As for the rain on the roof, did you consider the effect of falling water
>producing ions?  When I placed ions next to my coil, the inductance
>measurement changed considerably.  When I placed water next to the coil
>there was barely an effect at all.  You may be misinterpreting the mechanics
>of the weather.

You may want to try the ion thing next to just a wire or maybe just the
meter itself to be sure you are not seeing radiated noise affecting the
meter.  Guess how I know to check for crap like that :o)))  I only consider
the rain as a lossy material that is abosorbing the coil,s energy and thus
dropping the Q.  No fancy ionization has been considered at least by me.

>>I must write up the details or the data will be just as sketchy as
>We don't want that.  Let's get to the bottom of this.  I now have a personal
>interest in your data and results.

I'll try to get that done.  Been writing web pages all day and burnt now...
 It is non-TC related but:


Ouch!  Unlike everyone else, the moderator can smack me for sneaking in
non-TC stuff ;o))))