Efficient Tesla Coil
Subject: Efficient Tesla Coil
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Mon, 13 Feb 1995 23:51:00 GMT
>Received: from uustar.starnet-dot-net by csn-dot-net with SMTP id AA05760 (5.65c/IDA-1.4.4 for <tesla-at-grendel.objinc-dot-com>); Mon, 13 Feb 1995 18:22:15 -0700
Dan> Hello Everyone!
Dan> I've been reading and applying quite a bit of new
Dan> information here, and I'm going to go for the "efficient"
Dan> design during the next building period, which will begin
Dan> in a few days actually! Becuase of that, I kind of wanted
Dan> to go over the system and make sure that I don't have
Dan> too many misconceptions about what's what. So here
Dan> goes...(Please correct me as I go :)
Dan, I read over everthing, and it looks good to me!
Dan> Starting at the wall socket: A commercial line filter,
Dan> with a high enough current rating for the system, is
Dan> placed in-line with the power cord going to the, (in my
Dan> case), neon transformers. The filter is placed in-line in
Dan> reverse, as its job now is to keep rf out of the power
Dan> lines, not to keep rf out of the coil system. Therefore,
Dan> for the commercial filter, the "load" side goes to my
Dan> wall-outlet, and the "line" side goes to my transformers.
Dan> As I will be drawing about 15 Amps, a 20 Amp filter
Dan> should work ok.
Dan> (Power-correction capacitor goes here. Confused on
Dan> the calculation of this...)
Put the Power-correction capacitors as close to the neon primary
as possible. Given the massive error I made by interpolating
data, I understand and apologize for your misunderstanding.
Figure between 160 - 170 microFarads if you are using both
transformers with primaries wired in parallel on a 120 volt
Dan> I will be using two 15 kV, 60 mA transformers with
Dan> primaries and secondaries in parallel. These transformers
Dan> must be properly phased. (How does one check that
Dan> again?) The phasing can be altered by reversing the
Dan> primary's line connection. This should give me about
Dan> 1.8 kVA output. (15 kV * 120 mA)
I phase by wiring and firing... :-(
or is that firing and wiring... :-)
I use a length of solid polyethylene core from some RG-213 coax,
(shield removed) to bridge the hot terminals by hand. Wire the
primaries together and bring up the voltage a bit using a variac
(just to be a little safe...). If the ends of the two secondaries
to be connected together draw a hot 60 cycle arc when the
terminals are bridged with the coax core, the transformers are
out of phase. Reversing the primaries (or secondaries as
required) should bring the neons into phase with the result
result that only a tiny crackel of high voltage similar to a
static spark occurs when the secondarys are bridged with a
Dan> Next is the safety gap. This is a gap wherein each
Dan> side of the gap is connected to the HV out of the neon
Dan> transformer. Between those two gap-sides is a
Dan> grounded post. The grounded post is grounded to the
Dan> dedicated rf ground. The gap is set so that the
Dan> grounded post is between the two gap-sides, and so
Dan> that there is barely corona at the neon transformer's
Dan> operating voltage. This safety gap will sink any rf that
Dan> happens to get back through the system to the neon
Dan> transformer. (Is it ok/desireable to use points on this
Dan> gap, as opposed to flat faces?)
The primary function of the safety gap is not to sink rf really,
but to cancel and absorb HV kickbacks from the Tesla Tank
circuit. These kickbacks can puncture the potting of the neon
core, short out the secondary windings internally, and/or kick
back into the low voltage supply circuit. Both the core of the
neon, and the centerpost of the safety gap are connected and
grounded to the dedicated RF ground. Pointed gaps may be used
here if properly adjusted, but I have found that on systems this
size that a couple of brass bolt heads faced off with a grounded
plate between them work just fine.
Dan> Also, there should be rf-bypass caps across the
Dan> outputs of the neon transformer. There should be a
Dan> capacitance for each HV output, with one plate going to
Dan> the neon transformer, and the other plate to the
Dan> dedicated rf-ground. These capacitors should be low-Q
Dan> and lossy. (Like every capacitor I ever built! :) The
Dan> reactance of these capacitors should be _very_ high at
Dan> 60 Hz, but _very_ low at the operating frequency of the
This sounds OK, you want the bypass caps to bleed RF to ground
at the back end (supply side) of the Tesla Tank circuit. This
RF will be primarily at the system frequency, but harmonics would
ideally be bypassed as well.
Dan> Next, there should be rf chokes in series with the
Dan> neon's outputs and the primary discharge capacitor.
Dan> These should be made from toroid cores that can handle
Dan> the output of the power supply, and wound with heavy
Dan> wire. The reactance of the chokes should be _very_ low at
Dan> 60 Hz, and _very_ high at the system operating frequency.
Dan> This is the reverse of the bypass caps. (Could TV flyback
Dan> cores be substituted for the ferrite or iron-powder toroid
There is really no need to make this wire very heavy, but I like
to use a wire with a heavy insulation to prevent the inductance
from shorting during a HV kickback or similar incident (direct
secondary strike) headed in the direction of the supply circuits.
Number 12 stranded with a soft pvc jacket is fine. I wrap a layer
of electrical tape around the core before I wind on wire; as much
to prevent chips and cracks as to help reduce electrical break-
downs. These chokes are the first line of defence back to the
power supply: they draw the line between the 60 cycle on the HV
feed lines, and the HV RF hash from the Tesla Tank circuit. Some
people will place two sets of these chokes in each line, the
first set is placed right next to the tank circuit connection,
the second is placed right next to the bypass capacitors.
Dan> In my system, to begin with, I will have the single primary
Dan> discharge capacitor across the neon's outputs, rather than
Dan> try to run the "balanced" circuit right from the beginning.
Dan> This capacitor should be very high-Q, i.e., have a _very_
Dan> fast discharge rate. The capacitor should be tested to make
Dan> sure there are no internal resonances at or near the system
Dan> operating frequency. If the capacitor is not high-Q, then
Dan> peak powers-per-unit-time can never be realized. High-Q
Dan> capacitors can be built from ldpe and aluminum roof-
Dan> flashing. The value of this capacitor is based on the
Dan> impedance-match of the power supply.
Yup, sounds good to me! Without high Q caps, you can't get a high
Q coil system. It's pretty much that simple. Your looking at
about a .02 uF for this power supply.
Dan> The spark-gap should switch and quench as fast as possible,
Dan> which means _very_ fast. For higher powers, compressed-air
Dan> gaps are very good. The gap should be relatively massive in
Dan> order to promote cooling and reduce resistance to current
Dan> flow. The compressed-air gap allows faster switching while
Dan> maintaining a shorter gap. _Very_ high powers per-unit-time
Dan> can be realized. (Should other gaps be used in series with
Dan> this gap?)
You don't have to have a "massive" gap system if the gaps are
well thought out and constructed. This is right at the bottom end
of the power levels (~2kVA) where quenching the main system gaps
becomes "nighmarish". A single compressed air quenched gap will
handle this with ease, but for the $ you spend on a decent
compressor I will tell you that a well built vacuum gap would
also handle this without difficulty, and a lot less noise. If you
already have a compressor, and you don't mind wearing heavy ear
protection, compressed air gaps will really howl!
Dan> The primary coil should be a flat pancake or a saucer
Dan> shape. The diameter of this primary should be roughly
Dan> equal to the height of the secondary coil in order to
Dan> promote maximum flux-linkages throoughout the length
Dan> of the secondary coil. The primary should be made of
Dan> copper tubing, the larger the better. However, I will be
Dan> using #6 stranded, rubber-covered wire because I have
Dan> about 100' of it. I can always go to copper later :) I will
Dan> have about 12 taps per turn, equally spaced, and have
Dan> as many turns as possible.
Go with a "saucer" shaped (inverted conical section) primary with
this diameter secondary. You can save yourself a lot of work
cutting the rubber insulation for taps, you will only need about
4 taps per turn.
Dan> The secondary will be wound on 6" lucite, 24" long.
Dan> (Will it still be necessary to coat the form with
Dan> polyurethane before winding?)
No, lucite is acrylic, and very high Q. One thin coat of sealer
will help the wire stick down on the form (gives it a little
"bite"), and makes winding a little easier, but it is not
necessary from a performance stand point. The coil will perform
equally well if the wire is wound on the bare plastic.
Dan> The secondary will be totally sealed so that there are no
Dan> air-paths inside the coil that will allow conduction of
Dan> voltages to ground through the inside of the tube. There
Dan> will be no holes in the tube, nor will the wire ever enter
Dan> the tube. The mininum-allowable wire gauge is #22, which is
Dan> what I will use.
Dan> The bottom of the secondary will be connected to the
Dan> dedicated rf ground. The dedicated rf ground is a
Dan> 5' x 1" copper pipe driven straight into the ground and
Dan> connected to the system with, (of course), #6 stranded,
Dan> rubber-covered wire. There will be many coats of
Dan> polyurethane on this coil. There will be enough coats
Dan> when I can no longer feel the individual turns of wire.
I would think about beefing up the ground at this point. Your
peak powers from this system will easily top several hundred
killowatts, and if your capacitor and gap are really high Q it
will go even higher. I would expect that this system will produce
a 60" spark (five feet) with regularity. You are up to the point
where a "code" ground is not going to provide optimum perform-
ance, not to mention safety. I would feel better if you were
talking about three, perhaps even four times, the surface area
contact with moist earth. Three six foot lengths driven in a row
six feet apart, with depresssions around the pipes to collect
moisture. I would connect the pipes with 1" tinned copper braid
ground strap buried six inches deep. I would also water the
ground down a bit to increase the conductivity before I fired.
Dan> The secondary will be topped with a 20" across,
Dan> 4" cross-section, toroid. The toroid serves several
Dan> functions. First, the toroid protects the secondary
Dan> windings. (How does that work again?) Second, the
Dan> toroid acts as a capacitance at the resonant frequency,
Dan> overriding the secondary's internal capacitance, allowing
Dan> more current flow. Third, the toroid inhibits discharge
Dan> from the secondary, allowing power to build to high levels
Dan> before sparking occurs. Finally, the toroid acts as an
Dan> electron (charge-wave) accelerator by not allowing slow-
Dan> down of the electrons (charge-wave) as they leave the
Dan> flux-propulsion area :) The toroid then is acting as a huge
Dan> attraction-potential, which aids resonance, as relative
Dan> speeds are maintained as constants, (if not actual
I will let Mark Graalman respond to this, he definately had a
better hand on this. Mark care to comment?
Dan> The toroid should be raised high enough to not be affected
Dan> by the primary flux-paths, and also to reduce the chances
Dan> of arcs going to the power supply or primary circuit. It's
Dan> not a bad idea to put up spark-guards to give the sparks a
Dan> place to strike. These should be connected to the dedicated
Dan> rf ground.
This sounds good. Also, someone mentioned placing conductive
protuberances on the toriod to allow directed breakdowns of the
Dan> If I left out anything please let me know. Also, if any
Dan> improvements in the above system can be suggested, please
Dan> do so. I really want this one to be the best ever!
Dan> Thanks, Dan <klineda-at-univscvm.csd.scarolina.edu>
Hey you really have been doing your homework. The only weakness I
see is the ground, other than that this looks pretty cherry!
Should rate in the "Widamaker" class of coiling!
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12