[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: [TCML] Tim's Qs was: can you connect the secondary *directly* to the primary
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 2.5 inch
> 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
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
_________________________________________________________________
Boo! Scare away worms, viruses and so much more! Try Windows Live OneCare!
http://onecare.live.com/standard/en-us/purchase/trial.aspx?s_cid=wl_hotmailnews_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla