[Prev][Next][Index][Thread]
Re: Questions about first Tesla coil
Subject: Re: Questions about first Tesla coil
Date: Tue, 22 Apr 1997 07:13:11 -0700
From: "DR.RESONANCE" <DR.RESONANCE-at-next-wave-dot-net>
To: "Tesla List" <tesla-at-pupman-dot-com>
Hello Owen:
You might try a neon sign transformer instead of the 2N3055 ocsillator
driving a flyback xmfr. This setup will only produce 1-2 ma of drive
current. Usually you need around 30-60 ma of drive at 12 Kv which makes
a
neon unit a good start. Sometimes if you get the right shop owner and
you
are a student he will donate a unit to you --- never hurts to ask!!
A good suggestion not to use a pole pig until you have built a few
smaller
units first. Pole xmfrs are extremely dangerous and will fry you in an
instant.
You can obtain free details on a reasonable design by requesting the
"Small
Oscillator Design Guide" from Resonance Research Corp, E11870 Shadylane
Rd., Baraboo, WI 53913. Send a $3.00 priority mail stamp (no cash or
checks).
DR.RESONANCE-at-next-wave-dot-net
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: Questions about first Tesla coil
> Date: Sunday,April 20,1997 10:35 PM
>
> Subject: Questions about first Tesla coil
> Date: Sat, 19 Apr 1997 19:56:13 -0400
> From: "Owen Lawrence" <owen-at-iosphere-dot-net>
> To: <tesla-at-pupman-dot-com>
>
>
> Hello, fellow Tesla coil builders! I thought I'd finally
> introduce myself
> after enjoying the banter on this list for a few weeks now. My name is
> Owen Lawrence and I live near Ottawa. Like any beginner I'm bustin'
> with a
> million questions, so I'll pose a few of them now.
>
> When I was in high school I built a coil but was never quite
> happy with
> the results. However it was entirely my own design so I'm still proud
> of
> it. I'll describe what I can remember of it and you can tell me how I
> can
> do better the next time. I've always had this dream of doing it over
> again
> and getting it right, so here goes. The primary transformer was a small
> (brand new) ignition coil. Starting with six volts DC I created pulses
> using a relay wired to vibrate. My four capacitors wired in parallel
> were
> made of approximately one square foot of aluminum foil glued to each
> side
> of a slightly larger sheet of 1/16" plexiglass. Each capacitor was
> spaced
> an inch or two from the other. By my calculations at the time I recall
> assuming they were 50pF each, so 200pF in total.
>
> My spark gap was made from two small bolts. I filed off the
> threads near
> the end of one of them to make it round, and sparked to the head of the
> other bolt. With a nut on the threads and a wire attached to the nut I
> had
> an adjustable spark gap. Next, the primary winding was a cylinder of 14
> guage bare copper wire, maybe a dozen turns at one foot diameter, height
> of
> about 8" or 9" inches in total. In the middle of this winding was my
> secondary, which was about (and I'm really guessing here since I never
> did
> count, even back then) 800 turns of 32 guage enamelled wire on a 2" PVC
> pipe about 18" long, terminated with a 1/4" stove bolt. I don't
> remember
> at all how all of these parts were wired together. Does it really
> matter?
>
> In the end I was able to get sparks maybe 2" long. I could draw
> multiple
> fine threads of sparks from anywhere along the secondary by holding my
> finger near it. I had hoped for much longer sparks. Now I can see many
> ways this coil could have been improved but it has been dismantled for
> nearly two decades and I just want to learn what I can from it. I know
> it
> was functioning as a Tesla coil because I borrowed an oscilloscope and
> measured a frequency of roughly 32MHz with the typical damped envelope.
> You can't belive how excited I was in the middle of the night when I
> first
> applied power. Well, maybe you can.
>
> So here's my question: NOW it seems to me that 32MHz is much
> too high a
> frequency for this setup. Is it the length of the secondary winding
> that
> really dictates the best frequency for a Tesla coil (assuming no
> capacitance, that is)? I've tried out some of the formulas I've found
> in
> the archives and a more likely frequency seems to be in the
> neighbourhood
> of 2MHz. Is it possible my coil was resonating at a much higher
> harmonic?
> If so, could I have improved perfomance by adding capacitance to the
> tank
> circuit to lower the ring freqency to the same wavelength as my
> secondary
> coil? (Sorry if I get the terms mixed up; correct me where I'm wrong
> and
> I'll learn eventually) If my assumptions are not correct, can you tell
> me
> how you think this coil was performing?
>
> I would like to build a new coil and would like to use an
> ignition coil (I
> actually have the original one!) for my primary step up transformer.
> These
> things are limited in the amount of power they can output, so I was
> wondering what sort of spark length I should expect from a Tesla coil
> properly designed around this limitation. If all goes well, I will use
> the
> experience to take the step up to a neon sign transformer and see where
> that leads. I also have an old microwave oven in the garage with a
> blown
> transformer, whatever that means. Can anything be done with this? But
> I'm
> getting ahead of myself.
>
> As far as my primary winding goes, the dimensions I chose were
> completely
> arbitrary. It just seemed to look right so that's how I did it. Would
> I
> have benefitted from a smaller diameter? Many of the Tesla coil plans I
> see these days (in magazines or whatever) seem to have a tightly wound
> primary with a diameter only slightly larger than the secondary. I
> never
> liked these because they always used insulated wire which severly limits
> the choice of where it can be tapped. I can't remember exactly who said
> it, but since I've been devouring what I can find on the internet about
> Tesla coils I read somebody's remark that they preferred the shape of
> the
> field produced by a spiral coil over that of a helix. But that's where
> it
> ended. What's the real explanation here?
>
> Another question: I also own a high voltage power supply that I
> built
> from an Information Unlimited kit (30KVDC). I bet some of you are
> famliar
> with it, yes? Two 2N3055 transistors and a flyback transformer. Is
> there
> any reason why this wouldn't be good for operation in a Tesla coil? I
> would definitely want to protect the diodes in the high voltage
> rectifier,
> though, because they're expensive. I'm not gone on having a spark every
> 1/60th or 1/120th of a second, so if I have to wait while a capacitor
> charges that's fine. Whatever works best with the equipment at hand.
>
> Finally, I've seen some of the suggestions for building high
> voltage
> capacitors. One problem mentioned was that for rolled capacitors once a
> certain length is exceeded inductance starts to become a problem.
> Couldn't
> this be reduced by tapping off each plate along its length? When it's
> all
> rolled up the tabs from each plate could all be joined together so you'd
> be
> drawing off charge from the side of the plate rather than the end.
> You'd
> end up with terminals at each end of the capacitor. Excuse the artwork:
>
>
> ___|______|______|______|______|______|_______|______|______|__
> | + + + |
> ---------------------------------------------------------------
> (dialectric inbetween)
> ________________________________________________________________
> | - - - |
> --|-------|-------|------|------|-----|-----|----|-------|------
>
> roll it up: -------------------------------->
>
> | +
> / \
> |||||
> -----
> | |
> _____
> |||||
> \ /
> | -
>
> I have other questions (like, I still don't understand
> quenching, how much
> does a pole pig cost, and why isn't there a tesla builders' usenet news
> group) but these are the ones that have been nagging at me. Hopefully I
> won't be the only one that would benefit from answers to any of these
> questions. If you prefer to refer me to resources rather than answer
> questions directly, that's fine. Any response will be much appreciated.
> I'm very excited to have found such a cool bunch of people. I've
> already
> got several offices of people oooh-ing and ahhhh-ing over your pictures
> of
> operating Tesla coils I've downloaded (my wife is the only holdout :)).
> Thanks a million and I'll talk to you later!
>
> - Owen -