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Re: Interested in coils...

Subject: 
            Re: Interested in coils...
       Date: 
            Tue, 08 Apr 1997 19:05:06 -0700
       From: 
            Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: 
            Stoneridge Engineering
         To: 
            Tesla List <tesla-at-pupman-dot-com>
 References: 
            1


Tesla List wrote:
> 
> Subject:
>         Interested in coils...
>   Date:
>         Thu, 17 Apr 1997 20:55:38 -0400
>   From:
>         Corey Edmunds <corey-at-efni-dot-com>
>     To:
>         tesla-at-pupman-dot-com
> 
> Hi Everyone!
> 
> Just so you know, my name is Corey Edmunds.  I live in a small town near
> North Bay, Ontario, Canada. Im 15 years old and I am a interested in
> making a Tesla Coil.  I have poked through the archives -at- ftp.funet.fi
> and well i still have a few questions about materials/construction...
> 
> -Neon Sign Transformer
>         -How much should a used one cost
>         -What voltage/amperage should I ideally get?
>         -Where can I get one? (Local Neon Shop?)

Get them as cheaply as you can get from local neon sign shops,
demolition companies or even metal recycling junk-yards. The cost can
range from free (for old, out of warranty ones that have been pulled out
of service when signs are replaced) to $10-20 each for know used (but
good) ones. Old defective ones should be free or only a couple bucks (at
most). Avoid buying them new - they're horrendously overpriced and you
WILL blow them in Tesla Coil use. 

The voltage and current will govern how large a coil you can drive. A
small (3-4") coil will run just fine off a 7500 Volt 30 MA transformerr,
while a larger (8" - 10" diameter) coil may require a couple of 12 or 15
KV 60 MA transformers in parallel to run optimally. Ideally, try to get
a number of "freebies" that are the same voltage and current rating so
that you can parallel them and have spare(s) when you blow them... and
trust me - you WILL blow some of them! With some work, even defective
ones can often be made to work again. 

> -The wire
>         -Where can I get it from (A hardware store?)?

Typical place is motor rewinding shops. You can also order some from a
number of electrical and electronic supply places. Typical prices are $3
- $5/pound. Hardware stores typically do NOT carry magnet wire. If all
else fails you can try:

        The Coax Connection
        Joe Cassata KA9CAI
        10S226 Meadow Lane
        Naperville, Ill. 60564
        1-630-420-0342

Joe carries, or can get, virually any size/type of magnet wire, and he
LOVES Tesla Coil builders - let him know this is what you're using it
for!

> -Capacitor
>         I think i will try to make some sort of salt water-bottle
> capacitor.
> Would beer bottles & veggie oil         work in it?

As long as the beer bottles are the heavier, thicker, type. Some of the
newer screw-top, clear bottles are too thin. Try to find bottles that
have at least 1/8" wall thickness. The average capacitance of a small
beer bottle is about 600-750pF. If you plan on running off a 15 KV
transformer, you'll need to run paralleled groups of 2-3 of these in
series to withstand the voltage and get the proper capacitance.
 
> -Primary
>         -What's the dif. between an achemedes spiral and a pancake
> spiral?
>         -About how many turns should I use?
>         -What is the best material?
>         -What is the best shape?

These are different names for basically the same thing. The turn-to-turn
spacing is constant in an Archimedes coil (and is usually constant in a
pancake coil as well). Most coilers use heavy gauge wire (say #6 - #10
AWG for small coils), or 1/4" - 3/8" OD soft "refrigerator" copper
tubing. The advantage of the latter is the ability to easily connect an
alligator clip "tap" at any outer turn to adjust the inductance. The
"right" number of turns is that which makes your primary circuit
oscillate at the same frequency as the secondary. Plan on using 10-15
turns on the primary for good performance. The shape can be pancake,
helical or a combination (inverse conical) as long as you have adequate
clearance to the secondary. For simplicity and maximum toroid:primary
clearance, I'd recommend the pancake style. Remember to add a grounded
strikerail (but not a completely "shorted turn") above so that arcs
don't directly hit your primary. Also, make providion to raise-lower the
secondary versus the primary so that uyou can adjust the amount of
coupling between the two.

A number of very useful programs are on the Funet site which can help
you design your coil. If you use Excel, Ed Sonderman's program
(teslaexl.zip) is straightforward, easy to use, and you can directly
"see" how the program actually computes the results. These will get you
into the ballpark for your first design.

> -Chokes
>         I have a few "C" shaped things off a TV tube.  Would 2 taped
> together
> work for the ferrite cores?
>         (Just a curiosity..)

If you wound them with well-insulated wire, and insulated the cores.
Most core material is somewhat conductive. You can also use single-layer
air-core chokes (a single layer 6-8" long of #26-28 AWG on a piece of
2-3" PVC pipe) combined with safety gaps across the output of the neons.
Other coilers run "bare" - no chokes at all! Remember to run your GAP
across in parallel with the neon, not your salt-water caps.

> What is a VARIAC and what are they used for??

A Variac is the trade-name for variable auto-transformer. It has a
single winding on a toroidal-shaped core. One end of the device has all
the wires sanded down so that they are bare (but still insulated from
each other). A sliding carbon brush assembly allows you to "tap" any
turn on the device, permitting you to adjust the voltage to virtually
any level between 0-100% or 0-117% of the incoming line voltage
depending upon how the unit is wired. These are VERY usefull in coiling,
since they allow you to continuously vary the incoming voltage to the
neon transformers, permitting you to slowly ramp up the power rather
than only applying full power in an on-off mode. BTW, don't try to use
common solid-state lamp dimmers instead - the inductance of the neons
will toast these immediately.
> 
> Well thats about it...
>         Thanks!
>                 Corey Edmunds

The Funet site also contains some good articles on buiding gaps and
toroids. Also, the voltages and currents involved in Tesla Coiling are
not the only hazards you need to be aware of... please read the Tesla
Coil Safety Sheet on Chip's site before starting to build or test
anything:

http://bhs.broo.k12.wv.us/homepage/chip/safety.htm

Hope this helps. BTW, There are a number of other coilers on this list
in the Ontario area who also may be able to provide you with direct
assistance. 

Good luck, and safe coilin' to you, Corey!

-- Bert H --