Re: [TCML] Why don't big Tesla coils use helical primaries?

[bturner@xxxxxxxx]

Coupling is a factor, for large, high-power coil systems, a flat 'pancake'
primary offers several advantages, mostly from a practicality standpoint.
It's a LOT easier to add a riser or spacer to the bottom of the secondary
to adjust coupling (usually requires LESS height) AND the risk of
D'Arsonval breakdown (bottom windings of secondary arcing to the primary)
is reduced. Copper tubing also offers the advantage of a decent
cross-sectional area of conductor. (Less current 'bunching') BTW - my 4Kw
coil uses 1/4" copper refrigeration tubing in a flat primary, and after
10-15 min of operation, actually gets WARM. I used 4-gauge arc welding
cables to connect the primary loop together. A smaller gauge
insulated-wire primary presents a higher resistance/impedence translating
primary energy simply into heat. (Perhaps great if it's a cold night,
but...)

Doesn't help spark LENGTH, but whooo boy, that, along with my 600Bps sync
rotary gap and 0.06uf primary capacitance gives me WHITE-HOT secondary
discharges - a LOT of peak secondary impulse current to be sure.

Tesla DID use a two-turn insulated-wire primary in the Magnifying
Transmitter, but it was like 000 gauge or so, and also really big in
diameter, directly under the first secondary windings.


- b




> I've wondered why helical primaries aren't common in medium to large coils
> too.
>
> Can't over-coupling be moderated by enlarging the diameter of the primary,
> or by using a more insulating coil form?
>
> PBT
>
>
> ----- Original Message -----
> From: "Brandon Garretson" <garretsontech@xxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Wednesday, August 31, 2011 12:14 PM
> Subject: Re: [TCML] Why don't big Tesla coils use helical primaries?
>
>
>> Over-coupling.
>> Im sure someone will elaborate on that but the main reason for my reply
>> is
>> that I take exception to your statement that copper tubing primaries are
>> aesthetically unappealing.
>> I think they are the best looking part of many coils.
>>
>>
>>
>> On Wed, Aug 31, 2011 at 1:39 AM, James Hutton
>> <b-u-r-t-o-n-boy@xxxxxxxxxxx>wrote:
>>
>>>
>>> Hello,
>>> so I was just wondering why no one uses helical coils with insulated
>>> wire
>>> like this: http://www.johndyer.com/MakerFaireJD06.jpgwhen building big
>>> static gap tesla coils.
>>> I have seen tons of small sgtc's with a primary like that, but it seems
>>> that with bigger sgtc's people always use copper tubing and carefully
>>> space
>>> them in a flat or conical spiral.
>>> I don't understand this. Helical coils with insulated wire are so much
>>> easier to make, they cost less, their more durable, look better, and
>>> take
>>> up
>>> much less space.
>>> Is it because helical coils are less efficient?
>>> I need to build someone a nice looking tesla coil that is 900w
>>> (15/60nst)
>>> and makes ~4ft lightning. I dont want the base looking huge, and I
>>> can't
>>> spend a whole bunch of money on 50ft of copper tubing.
>>> Should I still go with a pancake type primary using the usual copper
>>> tubing? or can I just get a pvc pipe wider then my secondary and wind
>>> an
>>> insulated wire around it/
>>> and theres no way I'm air winding a copper tubing helical coil :P I
>>> dont
>>> know how people have the patience for that!
>>> thanks for the help!
>>>  _______________________________________________
>>> Tesla mailing list
>>> Tesla@xxxxxxxxxx
>>> http://www.pupman.com/mailman/listinfo/tesla
>>>
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