Re: [TCML] Tim's Qs was: can you connect the secondary *directly* to the primary

[David Dean <deano@xxxxxxxxxxxxxxxx>]

On Friday 16 November 2007 01:05:11 pm 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!! 
Yes it is!
This from last Fridays front page headline in the local paper.

http://www.sanmarcosrecord.com/local/local_story_313135256.html



> 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.
>
>
>
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