[TCML] Confusing Between 1/4 and 1/2 Wave Coil
jordancole at student.ednet.ns.ca
Fri Jul 29 18:18:21 MDT 2011
Yes, i meant a coil with two high voltage terminal. I dont plan on
using a center tap ground either and i'm planning on making it a
fairly lower powered coil ill be using a "weak" (fairly damaged)
10,000v 23mA OBIT. If its frequency is around 662 kHz, the primary
should be at the same frequency, true? Operates similar to a monopolar?
Thank you both.
Quoting Weinhold Shannon L <Shannon.L.Weinhold at doc.state.or.us>:
> One thing that might be helpful to know about bipolar coils is that they
> are actually two coils on the same former that are centerpoint grounded,
> usually with a space in the center, so as far as tuning is concerned,
> enter your parameters for the secondary based on 1/2 of the coil length,
> minus the gap in the center...just like it was a single coil. That being
> the case, bipolar secondaries need to be quite long to get good
> performance. If you wind them the length of a standard coil, you end up
> with the equivalent performance of two coils of half that length. So
> overall ratios of a bipolar should be somewhere in the 1:6-1:9 range. As
> far as winding the coil...you can just wind a continuous coil and do
> your lacquer treatment, and then go back later and cut it in the center
> and remove an inch or so of the middle windings, then tie the two ends
> together and design some sort of a (well insulated)ground connection
> from there.
> Its also possible to design/build a horizontal coil that is continuous,
> i.e. without center tap, but note that the primary to secondary coupling
> must be very loose, or you will have serious issues with racing sparks.
> The vintage ones I have seen were something like a 6" secondary and a
> 20-30 inch primary.
> Coupling on bipolars is a consideration as well. I built mine with a 4"
> secondary and an 8 inch primary former, and the coupling is still too
> tight. 12" probably would have been perfect.
> Hope that's helpful.
> Shannon Weinhold
> Klasdja Intelligent Innovations
> -----Original Message-----
> From: Jim Lux [mailto:jimlux at earthlink.net]
> Sent: Friday, July 29, 2011 7:51 AM
> To: tesla at pupman.com
> Subject: Re: [TCML] Confusing Between 1/4 and 1/2 Wave Coil
> On 7/29/11 4:20 AM, Cole Awesome-Jordan wrote:
>> Hi, I've had a bit of free time recently and i decided to go digging
>> for information on bipolar coils and the difference between 1/4 and
>> 1/2 wave coils.
> Aieee... Do not think in terms of wavelength and coil configuration.
> From a functional standpoint, lumped models are simpler, easier, and
> more accurate. That whole "wind a 1/4 wavelength of wire" thing was a
> coincidence for some shapes of coils that just happened to work sort of,
> but confused everything.
>> And I read this
>> however this got me quite confused on the subject. When you calculate
>> a "normal" coil with kHz=1/(2*?*L*C) is this half or quarter wave?
>> It's half isn't it?
> Neither.. that is the resonant frequency of the secondary LC
>> And if you have a bipolar coil that is 1000 turns of 26 gauge magnet
>> wire (55.25 turns per inch) and the form is 2.375" by 18.125"
>> (approx.) what is the frequency? Because I've been getting all sorts
>> of answers some say multiple the frequency by 2, another said
>> 1.38-1.4, and a really odd answer I found of 2.6 somewhere.
> When you say bipolar, do you mean a coil where both ends have HV
> electrodes on them, as opposed to the more conventional ground plane on
> one end, HV terminal on the other?
> The inductance of that secondary is about 6.9 mH. It's the self C
> that's going to be tricky. If it were vertical above a ground plane, it
> would be about 6.5 pF (for a fRes of 750 kHz, with no topload).
> The tricky thing is that the Medhurst formula
> a) starts to break down for large H/D, and you're at 8:1
> b) doesn't work for a "coil in free space"
> If you have a "pancake" primary in the center of the coil, then, you can
> probably use Medhurst, figure out the self C of a 9" long coil, and then
> double it.
> (that works out to about 4.2pF*2 or 8.4pF, by the way)
> So now, you're looking at LC of 6.9mH and 8.4 pF, which will resonate at
> I'm sure you'll have questions... ask away
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