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RE: [TCML] Bifilar coils
(post on behalf of Jeff Behary)
Shannon,
Please feel free to forward this email to TCML on my behalf, I am no longer a member. I'm happy to give my 2 cents though,for you and anyone else who cares... for what its worth.
I've had many questions regarding this topic, and the whole term is used so erratically by the pseudo-crowd, it only complicates matters.
Many people have referenced this as a Tesla Coil patent - because it looks like a Pancake Coil at first glance. The real patent with a Pancake Coil is here:
http://www.electrotherapymuseum.com/TeslaArchive/593138/pages/000593138-2.htm
It clearly shows a multi-layered secondary coil, and these are wound in the same fashion as a neon xmfr secondary coil, etc. Tesla originally used triple silk-covered
wire to wind his coils, with a wrapping of textile cloth between layers. The finished coils were placed in cardboard tubes, perforated, thrown in wax, and then boiled
until the air bubbles ceased. He later devised the whole vacuum impregnation process, and also to simplify things used space-winding techniques with normal wire to
save money. Others did this too, or variations of it, and most commercial Tesla Coils starting with Kinraide's in 1897 were adaptations of this technique - which was
widely used in the first few decades of the invention.
My opinion of the bifilar patent is rather boring. I take it for the title. "Coil For Electromagnets". My reasoning is this: if you look close at all of Tesla's original tabletop
coils, they all have one thing in common. Over a dozen designs, and yet not a single transformer or spark gap powering them. They were all variations of this:
http://www.electrotherapymuseum.com/2007/Oscillator/pages/Tesla%20Oscillator%202.htm
Electromagnets or "Self-Induction" Coils, "Circuit Controllers" - either mechanical interrupters or mercury interrupters (some hermetically sealed), a condenser in the base,
and a bipolar "Pancake Coil" of the type in patent 593,138. The "kicking coil" arrangement provides simple back EMF to charge the cap, and can be operated on DC or AC
universally. The design is very efficient, if many properly. It works really well for designs around 50 - 100 kHz.
Here is a simple setup that runs from 12V, produces over a 1" spark, and runs with as little as 1 BPS. Its crude, but so simple its rediculous. Very little wire involved, and very little voltage.
The back EMF is so handy for Tesla Coils, but not too handy for normal applications - like Relay's etc... espescially those without condensers where the arcing at the contacts
normally pits and consumes them over time. I believe this patent is a way of solving that problem for normal applications. I don't know how much its ever been put to use though.
I've seen a lot of free energy references to it and am a bit bewildered by the intense interest in them. Espescially when its so easy to make sparks from even a simple flat spiral - and
yet few attempts are made even to try this. (??)
I don't want to discourage anyone from trying, but for me I don't think this would work for a secondary coil. I *have* been experimenting though with lateral-wound and honeycomb radio coils for new applications, and though I can't figure out how to wind them yet (I have articles on the topic, but its like reading Greek to me!), they are interesting for experimentation. Here is a strange arrangement for making 12kV from only 750 turns of wire. It works just as well with normal layered coils, but these old radio tuning coils are so pretty its a shame not to put them to use...as far as I know, they haven't been used this way before:
http://www.electrotherapymuseum.com/2009/16Nov09/RadioInductionCoil.htm
and they can power a Tesla Coil too:
http://www.electrotherapymuseum.com/2009/16Nov09/RadioInductionCoilTeslaCoil.htm
Here is the same low volt circuit used with a Pancake. Note that the cap is a motor run cap! Far from a normal TC cap!
http://www.electrotherapymuseum.com/2009/15Nov09/LowVoltPancake.htm
Early setup photos:
http://www.electrotherapymuseum.com/2009/15Nov09/LowVoltExperiments.htm
For some other new/old ideas, here is a 1.5KW Transformer, made for free, from scrapped microwave transformers, a welder, and an angle grinder:
http://www.electrotherapymuseum.com/2009/08Nov09/SuperMOT.htm
Early testing photos:
http://www.electrotherapymuseum.com/2009/09Nov09/index.htm
The finished coil and power supply is only 9" in diameter and 36" tall. It makes a 24" hot discharge.
http://www.electrotherapymuseum.com/2009/15Nov09/CompactCoil.htm
I hope this helps, I also hope everyone on TCML is doing well. Times are very difficult recently for most, myself included.
Jeff Behary, c/o The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com
-----Original Message-----
From: Lau, Gary [mailto:Gary.Lau@xxxxxx]
Sent: Monday, November 16, 2009 4:59 PM
To: Tesla Coil Mailing List
Subject: RE: [TCML] Bifilar coils
The cited wiki page indicates that a flat bifilar-wound primary, with the two strands series-connected, was used by Nicola Tesla. I am by no means an historical authority, but this seems like an unlikely and ill-advised way to build any kind of high voltage winding, as one typically wants to keep the two ends of a HV coil as far from one another as possible. Primary coils for Tesla coils are never bifilar wound.
Some have suggested that a secondary winding may exhibit lower losses if two strands are wound in parallel, either side by side or one atop the other, to lower the effective resistance, but I don't think that a theoretical analysis or controlled comparison showed any improvement.
Your question about how to count the pair depends upon how the ends are connected. In the previous paragraph, the two parallel strands are counted as a single, fat strand. If the two strands are series-connected, then there would be twice as many effective turns and about 4X the inductance (but useless for a HV secondary).
Regards, Gary Lau
MA, USA
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Peter Baitz
> Sent: Monday, November 16, 2009 7:04 PM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] Bifilar coils
>
> Hi all,
>
> Questions about use of bifilar coils.
>
> http://en.wikipedia.org/wiki/Bifilar_coil
>
> I know this is used sometimes as a primary, but has anyone used it as
> a secondary? Further, when making a bifilar, does one count the
> *pair* as the winding, ie. 700 turns is 700 pairs, or does one count
> 350 turns counting both additively 350+350=700 ? I know this almost sounds trivial, but maybe it isn't?
> And does anyone know of a good bifilar calculator?
>
> Thanks
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