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Re: [TCML] Tim's Qs was: can you connect the secondary *directly* to the primary
Yep - I am looking at the scrap bin at work and picking out my bits of
phenolic and delrin to make a nice flat primary that was designed using
JAVAC already. I have been pacing myself - I promised that I wouldn't build
a huge coil to zap the neighbors until I had got a small coil working ... :)
Judging from what I have been reading - the small coils with the relatively
high first resonance frequency are problematic to build. I suppose that the
experience will be frustrating but instructional.
On Nov 16, 2007 8:45 PM, Scott Bogard <teslas-intern@xxxxxxxxxxx> wrote:
>
> Tim,
> Yes, that off axis inductance is probably killing you, a new primary
> should help, I would recommend a flat spiral primary over a helical, it made
> a big differance on my first coil.
>
> Scott Bogard.
>
> > Date: Fri, 16 Nov 2007 19:39:03 -0800
> > From: btmeehan@xxxxxxxxx
> > To: tesla@xxxxxxxxxx
> > Subject: Re: [TCML] Tim's Qs was: can you connect the secondary
> *directly* to the primary
> > CC:
> >
> > Thanks for the advice!
> >
> > I heard so much bad stuff about the wood for the spark gap, so I ditched
> it
> > and got a scrap piece of delrin and bored some holes in it for the spark
> gap
> > (until I get a better one at the hardware store this weekend).
> >
> > I have 2 foil capacitors (I guess - they aren't electrolytic, and they
> > aren't the pancake shaped ceramic ones ... they are about the size of a
> > cigarette lighter). They are 0.01 microfarad 8kV rated, in series, so I
> > figued that they were 0.005 microfarad 16kV or so. (Now that you guys
> > mention it - I never checked the capacitance to see if it was punched
> > through yet).
> >
> > The NST is 120V pri / 9000 V sec, 30mA, 270 VA. I am using a Variac to
> vary
> > the input also.
> >
> > I went back to measure the secondary. It is 989 turns of 28AWG on a
> > 1.5inch diameter phenolic tube. The height of the windings is about
> > 12.5 inches and there is 1 inch of tube above and below the windings.
> > JAVATC said that it should have a Q in my configuration near 200.
> >
> > I have a nice topload - a spun aluminum toroid from (
> > http://hometown.aol.com/futuret/page1.html) which measures roughly 2.5inch
> > minor diameter, 6 inch major diameter.
> >
> > I went back and ran with a ground connection to the secondary and got no
> > sparks again, so I decided that I would scrap my primary and go back to
> the
> > drawing board with JAVATC. When I ran it with the "tune my coil" box
> > checked and a test helical primary I noticed something else that was
> > probably messing me up. JAVATC said that with a 2-inch radius primary
> coil
> > I should have 6.8 turns, and that the inductance of the primary coil
> > was 5.7microhenry, and with 2 feet of primary leads (that were
> > 0.857 microhenry) ... however I had a lot more than 2 feet of cable
> there -
> > I had about 5 feet, and I coiled it up to prevent it from getting
> tangled up
> > and in the way ... so the primary leads probably had at least as much
> > inductance as the primary coil if not more.
> >
> > So, I'm probably going to be making some nicer secondary stands, and a
> > better RF ground needs to be located ...
> >
> > Thanks for all the tips
> >
> > On Nov 16, 2007 11:05 AM, <Mddeming@xxxxxxx> wrote:
> >
> > >
> > > Hi Tim,
> > >
> > > A complete answer to your questions will require more information
> than
> > > you provided. See comments interspersed below:
> > >
> > > In a message dated 11/16/07 1:56:03 A.M. Eastern Standard Time,
> > > btmeehan@xxxxxxxxx writes:
> > >
> > > "This is my first tesla coil, I built it without consulting any
> sensible
> > > source of information on the web."
> > >
> > > This is far more common than you'd think.
> > >
> > >
> > > "All I had was a healthy respect (fear) of high voltage and a neon
> sign
> > > transformer."
> > >
> > > A little fear and a lot of respect is healthy at this point. What
> voltage
> > > NST? What current rating?
> > >
> > >
> > > "I made a spark gap out of two screws and a u-shaped block of wood."
> > >
> > > NOT GOOD! At ~10 kV and above, wood, with any degree of humidity, is
> > > CONDUCTIVE!! Several heavy coats of varnish or polyurethane helps, but
> > > it's still
> > > better to use HDPE or similar plastic. For your gap, use 2 brass bolts
> > > head to
> > > head, or two round brass lamp finials, or two brass drawer pulls, or
> two
> > > round brass door knobs, etc. You can also use short sections of copper
> > > pipe in
> > > parallel but your sum of all gaps should not exceed 2kVrms/mm. Also
> use
> > > plenty
> > > of air flow, vacuum cleaner, fan, pressure hose, etc.
> > >
> > >
> > > "The choke coils are wound on a 3.5" long 3/8" diameter slugs of
> ferrite
> > > and they had a 1millihenry reading on the LCR meter at the office. I
> put
> > > them
> > > there to protect the NST, but I
> > > have since found out from members of this list that there are much
> better
> > > ways to do that."
> > >
> > > Ditch the choke coils, use a terry filter if you can, but at least use
> a
> > > safety gap. See the archives for details.
> > >
> > >
> > > "The secondary that I built had a 1.5" diameter, 10" tall and has a
> first
> > > resonance at about 500kHz. I used the frequency generator to drive
> the
> > > base
> > > of the secondary and read the peak from an oscilloscope probe used as
> an
> > > antenna."
> > >
> > > This is smaller diameter than most people build, but it's not bad for
> a
> > > first time. Without knowing what size wire and how many turns, it's
> not
> > > possible
> > > to analyze.
> > >
> > > "The primary is 15 turns in a flat coil with an inside diameter that
> is
> > > 1"
> > > away from the base of the secondary coil (3.5" diameter). The
> primary
> > > circuit and the NST are not grounded at all."
> > >
> > > Again, without knowing the spacing between turns, wire or tube size,
> or
> > > outer diameter, there's not enough to analyze. If this is fastened to
> a
> > > wooden
> > > board and/or your using metallic fasteners, you probably have a high
> > > resistance short circuit or two.
> > >
> > >
> > >
> > > "The capacitor is a 1 uF 20 kV rating that I borrowed from someone at
> the
> > > office. I did let them know that there was a fairly good chance it
> might
> > > not
> > > come back alive."
> > >
> > > What type - mylar, mica, foil, film, ceramic, etc?? NOTE: Your cap
> > > voltage
> > > rating should be not less than twice the output of your transformer.
> If
> > > you
> > > have a 12 or 15 kV NST you may have already punctured your cap.
> > >
> > >
> > > "I have a crude
> > > ASCII art drawing, (obviously this only works with fixed width font):
> > >
> > > +---CHOKE---+--||--+
> > > | | | o
> > > | v | |
> > > NST PRI SEC
> > > | ^ | |
> > > | | | |
> > > +---CHOKE---+------+---------+"
> > >
> > > Ditch the chokes and add a safety gap. The general layout is OK. You
> > > should
> > > have a least a Variac with a switch and a fuse for safety and control
> as
> > > a
> > > minimum. You can add metering, safety lockouts, contactors, etc as
> > > resources
> > > permit, and as your lust for power grows. (And it WILL!)
> > >
> > >
> > > "It never sparked, however I have more enthusiasm than smarts for RF
> ...
> > > I also had the spark gap about 1/4" apart, and when it ran there were
> big
> > > cloudlike angry blue sparks ..."
> > >
> > > Depending on the size of your NST, that may or may not have been too
> > > wide,
> > > as mentioned above.
> > > You may indeed have blown the cap and are now feeding all your power
> into
> > > the gap.
> > >
> > > "I am guessing that I am breaking about 20 good design rules at this
> > > point,
> > > so I sought help before I shocked myself or blew up my secondary
> coil."
> > >
> > >
> > > You got here, and enlightenment does not care which door you came
> through
> > > or
> > > how long your journey was.
> > >
> > >
> > > "I am open to all criticism of the design, or pointers - I have found
> > > some of
> > > the online resources for design such as JAVATC, etc. and I'll
> probably
> > > start working on version two using some of the designs that I see on
> > > other
> > > pages ..."
> > >
> > > Copying designs, even good ones, without understanding what or why,
> could
> > > be
> > > VERY hazardous to your health. Ask many more questions, read more on
> the
> > > principles and safety, and make haste very slowly.
> > >
> > > Thanks again,
> > > Tim
> > >
> > >
> > >
> > >
> > >
> > > Welcome,
> > >
> > > Matt D.
> > >
> > >
> > >
> > > ************************************** See what's new at
> > > http://www.aol.com
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> > >
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