[TCML] can you connect the secondary *directly* to the primary?
btmeehan at gmail.com
Thu Nov 15 23:38:04 MST 2007
This is my first tesla coil, I built it without consulting any sensible
source of information on the web. All I had was a healthy respect (fear) of
high voltage and a neon sign transformer. I made a spark gap out of two
screws and a u-shaped block of wood. 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.
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
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. The capacitor is a 1uF 20kV
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. I have a crude
ASCII art drawing, (obviously this only works with fixed width font):
| | | o
| v | |
NST PRI SEC
| ^ | |
| | | |
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 ...
(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.
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
On Nov 15, 2007 6:03 PM, Scott Bogard <teslas-intern at hotmail.com> wrote:
> Yes, that is fine. the reason it is fine, is that it is grounded, so the
> RF currents do not seek a path to the ground through your transformer
> windings. Also, it is not a center tapped transformer, so the ground
> actually is the ground, not 5kV- or so. Just don't ever touch the
> output on your coil, and don't step on your RF ground cable! I believe
> Scot Dingman uses that setup, only with two piggies, and it works well.
> Scott Bogard.
> david baehr wrote:
> > ...my little 4" dia sec. coil is powerd by a single bushing (mini pig
> ) 1.5kva ,.....the bottom of sec. coil , inside of primary , and mini pig
> case are all tied to a single ground , is that OK ??
> > Thanks,dave
> >> From: Gary.Lau at hp.com> To: tesla at pupman.com> Date: Thu, 15 Nov 2007
> 13:56:34 +0000> Subject: RE: [TCML] can you connect the secondary *directly*
> to the primary?> CC:>> Connecting the secondary base to the primary is bad
> for several reasons. It should work just fine, but...>. But if the inside
> primary lead can be grounded, there may be insulation advantages to
> connecting the secondary base directly to it.>> Regards, Gary Lau> MA, USA>>
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