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RE: A few Q's
Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jim-at-jlproduction-dot-com>
Hi Terry (and others),
In regards to "skin effect"-
If that is the case (aluminum is lossy) then a large chunk of aluminum
would be a bad choice for a grounding block?
What I needed was a place to "tie in" all my RF grounds to one common
point
and then attach that point to my earth pole in the yard. This, in an
attempt to avoid multiple, long lengths of heavy cable to the ground
rod. I was going to grab a big hunk or cast iron or steel from work but
it was
suggested to me than aluminum would be a better choice. I ended up
grabbing an old cylinder head that is almost 100% aluminum.
So is this a good choice or would steel or cast iron be better after
all?
Thanks,
Jim Layton
-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, March 12, 2002 8:04 PM
To: tesla-at-pupman-dot-com
Subject: Re: A few Q's
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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