Re: Tesla coil grounding and other questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Brian" <ka1bbg-at-webryders-dot-net> 

Hi, go to the nearest Spa and pool installer, they will have all kinds of
white pvc left overs. cul brian f.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, February 15, 2004 7:39 PM
Subject: Re: Tesla coil grounding and other questions


 > Original poster: JOSEPH CACCIATORE <jocatch-at-us.ibm-dot-com>
 >
 >
 > Bert, thanks for the excellent comments. I was all set to rebuilt my
 > original until you said this transformer is capable of suppling 3-4'
 > sparks! I said to my self, WOW! Lets go for it!
 >
 > So now I am going to design and build a coil from scratch. I have seen a
 > few sites with design guidelines. I think I want to decide on a secondary
 > coil size and then figure out the primary specs as opposed to fixing a
 > primary coil size and tuning the secondary to match. Seems easier the
first
 > way. I plan to go to Home Depot and see how much 4" or 4.25" PVC pipe
cost.
 > Not cheap I don't think but I haven't seen anything else that would make a
 > good coil form.
 >
 > Regarding grounding, I am still not 100% clear. Can I just connect the
 > bottom of the secondary to the case of the NST and not use an earth or
 > outlet ground?
 >
 > Regarding spark gap I thought I was going to use two pieces of wire but
now
 > I am finding out that that is wrong too! 8-(. I was told to use like 1"
 > copper pipe x distance apart. But how do I easily adjust the distance
 > between 2 pieces of pipe?
 >
 > Well, got to go and start reading how to design the circuit.
 >
 > JC
 >
 > P.S. I don't know how this works, responding to a post in the list. The
 > instructions for this list regarding posting, responding to post, etc are
 > nil. If this isn't the proper way to respond, please tell me.
 >
 >
 >
 >
 > "Tesla list" <tesla-at-pupman-dot-com>
 >
 > 02/13/2004 10:59 PM
 > To
 > tesla-at-pupman-dot-com
 > cc
 > Subject
 > Re: Tesla coil grounding and other questions
 >
 >
 >
 >
 > Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net>
 >
 > Hello Joe,
 >
 > You may wish to do some research on current Tesla Coil designs
 > before going too far on rebuilding your coil. I remember when this article
 > first came out (I was in high school at the time). I was playing around
 > with a 2 kW VTTC coil using three VT4C/211A's in parallel. Never lost the
 > "bug"... :^)
 >
 > I had thought of scanning in this particular Popular Electronics article
 > and putting it up on my web site, but I decided against it because it had
 > so many problems and fundamental design flaws that severely limited its
 > performance, and I feared that it would mislead folks. Unfortunately, some
 > of the flaws were outright dangerous to to the continued survival of your
 > 12 kV 30 MA Neon Sign Transformer (NST) or the coil's operator and
 > observers. The specific design problems include the following:
 >
 > 1. The glass plate tank cap was connected directly across output of the
 > NST. We (now) know that the spark gap should be connected across the NST
 > and the capacitor should be in series with the primary winding (i.e.,
 > swap the gap and the tank cap location on the schematic). This minimizes
 > the degree of RF voltage that can "back up" into the fragile windings of
 > the NST.
 >
 > 2. The spark gap should have more robust electrodes and air cooling to
 > prevent overheating and improve quenching (which improves coil
 > performance). The recommended spark gap of 1" is much too far and creates
a
 > high risk that the NST will be overvolted and quickly destroyed.
 >
 > 3. There was no provision for tuning the coil (via primary tapping) or
 > to easily change the primary-secondary coupling. As a result the
 > original coil appeared to be grossly out of tune and a poor performer. The
 > cover shot for the magazine shows weak corona off the top of the coil
 > that's perhaps 2" long at best. Current designs using the same transformer
 > can achieve 3-4 feet
 >
 > 4. There was no provision to connect an RF ground to the system. Instead,
 > one of the HV outputs of the 12 kV NST was directly connected to the base
 > of the secondary (very dangerous!). This raised the potential of the
 > secondary to 6000 volts at 60 Hz! It then channeled the RF current from
the
 > base of the secondary into the HV input of the NST!
 >
 > 5. The glass plate capacitor is quite fragile, very lossy, and it
 > generates huge volumes of ozone. An up-to-date MMC capacitor (a
 > series/parallel combination of low cost polypropylene foil snubber
 > capacitors) will be virtually maintenance free, cheaper, self healing,
 > and will deliver much better performance. Some doorknob caps could also
 > work, but the type you'll want to use are designed for pulse duty, and
 > sometimes appear on eBay as ceramic "laser caps".
 >
 > 6. The design has no topload capacitance (toroid). The original design was
 > such a poor performer that no toroid was needed. However, if the above
 > design flaws are corrected, corona will break out from along the top of
the
 > winding, and this will char the top of the coil form.
 >
 > 7. Finally, there are no RF filters or any safety gaps to help protect the
 > NST from conducted RF or accidental excessive voltage conditions.
 >
 > Continue reading the Pupman or T-2 lists and please explore the archives.
 > You'll rapidly come up to speed as far as Tesla Coil technology for this
 > century and avoid many potential pitfalls. And I'm sure you'll get
 > excellent help and suggestions from many of the great coilers on both
lists.
 >
 > Welcome aboard and good luck!
 >
 > -- Bert --
 > --
 > ---
 >  >Original poster: JOSEPH CACCIATORE <jocatch-at-us.ibm-dot-com>
 >  >Hello. I am trying to resurrect my old tesla coil I made in high-school
30
 >  >years ago with plans that came from the July 1964 Popular Electronics
 >  >magazine. I still have the secondary coil and 12kv, 30ma NST which I
want
 >  >to use. The secondary was built pretty close to the article, 4.75"
 >  >diameter, 34.625" long using #26 (or was it #28) wire. The NST is center
 >  >tap to the case.
 >  >First question is grounding. The 120 vac for the NST of course is not
 >  >grounded (only 2 leads to the outlet). The design I have shows the
bottom
 >  >of the secondary connected to one side of the primary tesla coil in an
 >  >auto-transformer arrangement. That is how the original design worked and
I
 >  >was able to get 2 or 3" sparks from it.
 >  >But reading on the net I see some places which say ground the bottom of
 >  >the secondary to the case of the NST only and some show the bottom going
 >  >to earth ground only. Which is correct? If I want to run it in a house
or
 >  >display like at school, there won't be an earth ground to begin with.
 >  >Also, if you have seen the PE issue, they had the spark gap in series
with
 >  >the primary but all circuits I see on the net today shows the capacitor
in
 >  >series. Is that better?
 >  >For the capacitors, I am using thick window glass and aluminum foil,
each
 >  >glass is about 18"x18". I am using 2 of them.
 >  >Lastly, since I have about 75' of 15kv wire I want to make the primary
 >  >using the wire in a helical coil arrangement (I don't have copper tubing
 >  >nor anyway to bent it nor a mount for it). I assume I will need all the
 >  >wire since my basic calculations show I would need 52 turns for the
 >  >primary. Since 52 would require more wire than I got, could I go with a
 >  >harmonic and use 26 turns for the primary?
 >  >Thanks for any input you guys may have. I got this beautiful secondary
 >  >coil I made and NST and I really would like to make it work.
 >  >JC
 >  >
 >  >.
 >
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