Re: Bipolar Tesla Coil
Subject: Re: Bipolar Tesla Coil
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Fri, 19 Jan 1996 01:53:00 GMT
>Received: from uustar.starnet-dot-net (root-at-uustar.starnet-dot-net [184.108.40.206]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with SMTP id VAA17259 for <tesla-at-grendel.objinc-dot-com>; Thu, 18 Jan 1996 21:57:36 -0700
* Original msg to: Esondrmn-at-aol-dot-com
* Carbons sent to: usa-tesla-at-usa-dot-net
>> He has ordered one of the Condenser Products .025 mfd
>> capacitors so I thought we shoot for a frequency that would
>> allow him to use that. He has a 4.0 ft x 12" form. Ed S.
> This aspect ratio is a little low for a bipolar secondary, but
> it is workable. I would shoot for something a little closer to
> a 6:1 aspect ratio, allowing a 3:1 aspect between the
> mid-point on the coil and each end. Richard Quick
ES> It sounds like we should be using a 6" dia form about 36"
ES> long. That would get us right at 6:1.
Yup, this has worked very well in my experience.
>> I did some rough calculations today and came up with some
>> numbers. For a normal 1/4 wave Tesla coil we want about 900
>> turns of wire. With this type of coil I think we want 1/2
>> wave - or twice the amount of wire. Using 1800 turns of wire
>> (he has #25) we come up with a self resonate frequency of
>> about 69 khz. Ed Sonderman
>> In order to use his capacitor, we come up with a primary that
>> is about 20 turns of 3/8" copper tubing on .75 centers wound
>> on a 24" form about 15 inches long. Ed Sonderman
> Humm, I detect a problem here. The bipolar coil will actually
> act as two 1/4 wave coils with a null voltage point in the
> middle of the winding. In order to tune a tank circuit to fire
> a bipolar coils, you must calculate the 1/4 wave frequency,
> then multiply by two, to get the tank circuit frequency that
> properly tunes for this configuration. Richard Quick
ES> Understanding that we probably want to change the form, but
ES> for discussion, using the 12" dia form with 35" of windings,
ES> I calculate a resonate frequency of about 69 khz. Are you
ES> saying we want to design the primary for 138 khz?
What you have in a bipolar coil are two 1/4 wave voltage peaks
that are working off of a null voltage nodal point in the center
of the winding. To properly excite any coil to produce 1/4 wave
sparks you must tune the tank circuit to the same frequency as
the 1/4 standing waves you desire to produce. But what is the 1/4
wave frequency of a bipolar coil where there are two voltage
The actual 1/4 wave "length" of the bipolar coil (null voltage
node in the middle) is 50% of the 1/4 wave length of the same
winding with a null voltage node on one end. The simplest way to
figure this, given the abundance of 1/4 wave math on this
subject, is to calculate the 1/4 wave frequency of the entire
winding, then multiply this 1/4 wave frequency by two. This gives
the correct tank circuit frequency required to excite the coil in
order to produce two 1/4 wave voltage peaks.
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12