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RE: [TCML] General Questions About a Pig Powered Coil (andanIntroduction)
Thanks for the welcome!
The "pig" is a 15 KVA unit; the primary (my secondary) voltage is listed as 7200/14400 and the secondary (my primary) is listed as 120/220. I will be running it on 120 because I'd like to make this coil "portable" for some demonstrations (this is one reason for the variac). I do not believe these locations have 220 volt access, so I must be content with 120.
The variac consists of three units stacked in one. I was thinking I could use one of the variacs as an inductive choke (i.e. "ballast") for my pole pig by wiring the primary in series (and leaving the adjustable tap unconnected) with the pig. I'm not sure whether this will provide enough of a choke, however. I could wire two of them in series or, if that is still insufficient, I can probably dig up a surplus choke from the cloud chamber. Like I said, this variac is rated for an almost absurd current, IIRC so I think it should work well, even if I run at 120 volts and 30 amps.
I don't want to shoot myself in the foot before even starting, so if the general consensus is to make a bigger secondary, a bigger secondary I will make! However (embarrassingly) the longest lathe I own is only 30 inches. In fact, I've somehow collected three 16 by 30 American Pacemaker lathes. Absolutely fantastic machines - some of the best ever made ... but also very "stubby" (despite being only 30" between centers, these bad boys whey 7200 lbs a piece). I can squeeze about 32" but that is about all I've got - if I really had to, I could wind the first portion on the lathe and then <shudder> do the last several turns by hand.
I've got a big role of surplus 23 awg magnet wire, so I'd surely like to use it instead of buying heavier gauge wire.
Now I've read that the length of the secondary conductor should be roughly 1/4 of the resonant frequency wavelength. I've not really though about why this should be the case - I understand the necessity of matching resonant frequencies between the two LC circuits but this requirement regarding the length of the conductor was not immediately obvious to me.
Once I get a design set for the secondary coil, I can calculate the needed capacitance and sizes of the other components readily. I just need to "fix" some of these parameters - there are too many variables floating around! :-)
I guess the final question is regarding capacitors. Does anyone know of a good source for surplus or otherwise cheap capacitors for a MMC setup? I've got a bundle of ultra-low esr, low loss high pass capacitors for microwave experiments. The only trouble is they are 0.0047 microfarad and have an impractically low voltage rating...
From: tesla-bounces@xxxxxxxxxx on behalf of David Rieben
Sent: Wed 3/24/2010 2:01 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] General Questions About a Pig Powered Coil (andanIntroduction)
Welcome to the hobby. From reading your post
and from the mention of your "real job" pedigree,
it sounds like you should already be adequately
informed on the basic concept of operation ;^)
I guess the only thing that puzzles me is why you
would want to limit the size of your proposed
secondary coil to 8" x 25", considering that you
have a massive variac assemby and a pole pig. I'm
assuming that your pig is of the typical coiler's
size choice range of 10 or 15 kVA and 14,400
volts? I mean it seems like you would be severe-
ly limiting the potential of your power supply to
"choke" it back to a 120 volt, 30 amp service
and "only" be shooting for 6 ft. discharges. And
trust me, if you are like 99% of the rest of us
coilers, those 6 foot discharges will be very im-
pressive at first light but you will soon grow bored
and want BIGGER sparks, especially when you al-
ready have a very adequate power supply to readily
accomplish that. And you certainly have the power
supply hardware already in tow for easily making
sparks 3X that, assuming that you obtain and/or
build the rest of the coil system components to spec.
Then again, you may be space challenged for storage
and/or operation of a giant Tesal coil, too - kind of
where I'm at with my current coil system.
Anyway, the you should normally aim for a secondary
coil aspect ratio (length vs diameter) in the 3:1 to the
5:1 range and a topload toroid with a major diameter
about equal to the secondary coil length and a minor
diameter about equal to the diameter of the secondary
coil. SO if you secondary coil is 8x25, that would also
be a good appr. size dimension to aim for with your
Good luck with your project,
----- Original Message -----
From: "Thomas Schmit" <Thomas.Schmit@xxxxxxx>
Sent: Tuesday, March 23, 2010 5:59 PM
Subject: [TCML] General Questions About a Pig Powered Coil (and
I've never used a mailing list like this before, so you will have to
excuse any faux pa regarding the use of said list. For a quick bit of
background, I am a machinist and high energy physicist and it seemed
time that I build a Tesla coil. (No self-respecting physicist can
neglect to build one ;-) ).
I have a 3 phase variac (used for a cloud chamber, originally - its
good to 100 amps and 600 VAC RMS), a single phase pole pig, an old
mil-spec 30 KVDC 5 ma supply, several neon light transformers, etc.
That being said, I'm new to the home-brew high voltage game. It is
considerably different than working for a lab where dropping $10,000
on a power supply is trump change :-D and I could use all the help I
What I am concerned about now is the design of my coil. I am building
with a 6' spark in mind - that should pretty well max out a 110 volt
supply (the pole pig will be fed through one of the variacs hooked
into 110 volt mains through a 30 amp breaker). I'm looking at a
secondary coil with about 1000 turns of 23 AWG wire, which works out
to a length of only about 25". I am concerned about strikes hitting
the primary coil from the discharge terminal on the secondary.
I guess I was just hoping I could get some input on the secondary
design. I'm thinking an 8" diameter PVC form - I will clean, bake and
shellac it before winding my coil. Size/length/diameter of wire/number
of turns - these are all variables that I'm not to sure about. I know
what inductance I want to hit, but I can get there several different
ways and I figure you all have already done the hard work for me ...
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