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Re: sign xformer parameters for a particular Tesla coil?
Subject: Re: sign xformer parameters for a particular Tesla coil?
Date: Mon, 28 Apr 1997 00:03:31 -0700
From: "DR.RESONANCE" <DR.RESONANCE-at-next-wave-dot-net>
To: "Tesla List" <tesla-at-pupman-dot-com>
Hello Owen:
The basics go something like this: You match the impedance of the neon
xmfr with the impedance of the capacitor (capacitive reactance at 60
HZ).
A 30 ma xmfr matches to approx. a .005 MFD cap and a 60 ma xmfr matches
approx. to a .01 MFD cap. Step two is to match the resonant freq of the
primary circuit (combination of cap and primary inductor) such that the
resonant freq. will match the resonant freq. of the secondary inductor
with
HV terminal attached. If all this sounds like Greek your best bet would
be
to use a proven design to start with. Several books are out on the
subject
and John Couture's Tesla Coil Handbook is one of the best with lots of
charts and graphs to guide you in your design. You can reach him at
619-578-6376. You might also wish to join the TCBA (Tesla Coil Builders
Association) which publishes a quarterly newsletter that is very
informative. Contact Harry Goldman at 518-792-1003 for more
information.
Good luck.
DR.RESONANCE-at-next-wave-dot-net
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: sign xformer parameters for a particular Tesla coil?
> Date: Sunday,April 27,1997 10:08 PM
>
> Subject: How do you determine neon sign xformer parameters for a
> particular Tesla coil?
> Date: Sun, 27 Apr 1997 20:58:10 -0400
> From: "Owen Lawrence" <owen-at-iosphere-dot-net>
> To: <tesla-at-pupman-dot-com>
>
>
> (I already tried to send this message to the list and got no feedback or
> return copy, so I'm trying again. My apologies if I'm the only one that
> didn't see it. - 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
>
> Thanks for your response. What assumptions are being made to arrive at
> these specs ("need 30-60ma at 12KV")? I intend to build a small (but
> hopefully effective) coil to begin with. If I know ahead of time I only
> have 1-2ma to work with, I should be able to design around that.
>
> I have found several neon sign companies in the yellow pages,
> some within
> walking distance of where it work. I can't believe I never noticed them
> before. I'll be scavenging for transformers this week.
> If I'm offered any that don't work should I take them? Can someone
> point
> me to some hints/instructions on how to repair/recondition old neon sign
> transformers? Wish me luck!
>
> > 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.
>
> I intend to stay very far away from them until I know what I'm doing.
> At
> this point I consider neon sign transformers very dangerous. I'm just
> curious how you folks go about procuring one of these bigger ones. If I
> don't know what they're worth I won't know if I stumble across a good
> buy
> and should grab it for one of you, if not for myself :)
>
> I called a motor shop yesterday for a price on wire. I was told
> it's
> $16(Cdn)/lb, no matter what guage. So I found some tables of values
> adopted by AIEE in January, 1914 and still in effect (as of 1977)
> showing
> the following:
>
> AWG ft/lb ohms/1000ft diameter(mm)
> 32 5160 162 .203
> 30 3300 104 .254
> 28 2080 65.3 .320
> 26 1310 41.0 .404
> 24 818 25.7 .511
> 22 516 16.2 .643
> 20 323 10.1 .813
> 18 256 8.05 1.02
> 16 128 4.02 1.29
> 14 80.4 2.52 1.63
> 12 50.6 1.59 2.05
> (for amusement:)
> 56 1 380 000 43.2k .012 (over 261 miles/lb!)
>
> Sorry I can't quote the reference, I just have photocopies. I CAN get
> it
> from a friend if you're interested. The table includes all values from
> 56
> down to 4/0, and even values up to 56. I thought these might be
> pertinent.
> If you're interested in a guage not shown let me know. There are lots
> of
> other formulas such as relation between temperature, conductivity and
> resistivity of copper, but this is getting pretty picky for me.
>
> While looking up this table, there on the previous page was the
> formula
> for skin effect, which I recall someone asking about recently.
> Here it is:
>
> "The current intensity falls off exponentially with depth. The depth of
> penetration (s=sigma) is the depth at which the current intensity has
> fallen to 1/e of its value at the surface, where e equals 2.718...
>
> At three- and four-times the depth of penetration, the current intensity
> is
> 5 percent and 2 percent of that at the surface respectively.
>
> Where the diameter of the conductor is large compared to the depth of
> penetration, the total current is the same as if the surface current
> intensity were maintained to a depth of penetration.
>
> s = 503.3sqrt(rho/(urf)) millimeters
>
> rho = resistivity in ohm-meters
> = 1.72x10e-8 for copper
> = 2.83x10e-8 for aluminum
> ur = mu r = relative magnetic permeability
> = 1 for both copper and aluminum
> f = frequency in magahertz
>
> For example, for copper the depth of penetration is as follows:
>
> MHz Depth of Penetration sigma (mm)
> .1 .209
> 1. .066
> 10. .021
> 100. .0066
> 1000. .0021
>
> Sorry, .1 is the lowest frequency it gives. Anyone know the quanities of
> skin effect for skin?
>
> I hope you find this information of use.
>
> - Owen -
>
>
>
> owen-at-iosphere-dot-net
> http://www.iosphere-dot-net/~owen