Re: A few Q's

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

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

Hi Jim(?)

At 06:57 PM 3/12/2002 -0500, you wrote:
>Hi all,
>As I approach the finish line on my first coil, I have a few questions
>and afterward a comment.
>
>1) What is "Q"?
>I keep seeing references to this mystery anacronym, and have never seen
>it defined. For example This metal has a high "Q" or that capacitor has
>a low "Q". Could someone define this please?

To put it simply.  Q is a measure of some things ability to "ring".  If you
strike a clump of clay with a hammer (low Q) is just makes a thump.  If you
hit a tuning fork (very high Q) it rings for a long time.  Tesla coils are
the same way.  If they have low Q, they resonant for a short time before
the resonance is damped out.  If they are high Q, they resonant for a long
time.

High Q things have low losses while they oscillate and thus can oscillate
for a long time.

As you can imagine, giant math equations can be tied to all this too... 

>
>2)What is "SKIN EFFECT"?
>I had always thought that this was a commonly misused term referring to
>the idea that high frequency voltage passes along the outside of skin
>therefore making it a safe type of current. I know that this is at least
>partly not true and dead you will be if you happen to ground out back to
>the primary or wall outlet via your skin effect current. Recently I
>heard this term used about aluminum vs steel and it was tossed in that
>aluminum was a better choice as it has less "skin effect" Could anyone
>clarify this term?

RF currents flow in the top "layer" of a conductor.  Many conductors work
just as well if they are tubes instead of solid at RF frequencies.  At
13.56MHz, the current is mostly flowing in the first 0.0007 inch of a
copper conductor.  Inside there is no current flow.  Aluminum has a thick
oxide layer that hits this RF conduction layer causing high losses.  Copper
does too but it is not as bad.  Often a coating of silver or gold greatly
helps to prevent RF loss when high current is needed.

If the math of Q seemed complex, you have not seen nothing yet when it
comes to trying to figure out skin effect is some situations...

>
>3)Is a fluorescent bulb safe to hang on to near a coil?

No.  It does present some resistance, but it is much like holding a metal
rod to a coil.  If you get a good shock, you may crush the tube in your
hand.  A lot of people do this but it is not "safe".

>In a recent query about tuning a coil I was told that at low power(via
>my Variac) a bulb held near the toroid would help indicate proper tune
>with it's brightness(or lack thereof). Good idea or nay? 

Works well, but I would not hold it.

>Using the
>software Tesla CAD I determined that tune would be between #10 and 11
>turn so I put my clip at 10 1/2 turns. How close will this be and can I
>just "wing it" from there, or is the bulb a more accurate indicator? Is
>the latter even safe to try?

You should move the tap point around a bit in that area and find just the
best spot.  The programs are good, but not perfect, so a little fine
adjustment helps.

>
>I would like to say at this point in my project that I have a tremendous
>amount of time and energy into this. When I started this project several
>years ago I never dreamed it would be so intensive. It has been however
>one of the more compelling things I have ever attempted and without all
>of you (and coilers elsewhere) I never would have made it this far. I am
>certainly not at your level of electrical or theoretical expertise, and
>often I am just plain lost by some of your discussions, but it has sure
>been a fun trip anyway. Here's to big sparks and arks in the near future
>(like this weekend)!! Thanks to all,
>Jim L 
>http://www.jlproduction-dot-com/Tesla.html

I have notice that there are a few people that put a lot of effort into
coiling  :-))

Cheers,

	Terry


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