[TCML] Bifilar coils
harvich at yahoo.com
Mon Nov 16 20:22:26 MST 2009
--- On Mon, 11/16/09, Peter Baitz <ussenterprisencc1701 at rocketmail.com> wrote:
> From: Peter Baitz <ussenterprisencc1701 at rocketmail.com>
> Subject: [TCML] Bifilar coils
> To: tesla at pupman.com
> Date: Monday, November 16, 2009, 7:03 PM
> Hi all,
> Questions about use of bifilar coils.
> I know this is used sometimes as a primary, but has anyone
> used it as a secondary?
My largest 6 in diameter secondary was constructed with an extra winding around the first one when I had decided to do this at the end of a 70 lb 23 gauge Essex wire spool rewinding. At the time I had such a use for multiwound solenoidal layered secondaries which was used for the purpose at hand, but the project proved too costly and not justified by other tests on the same idea on a smaller scale. Such a secondary is probably useless as a TC secondary because of the internal capacity bet ween winding layers. However such tests could still be made by finding the secondary resonant frequency and primary LC matching it by signal generator means. This is one of my winter garage projects.
Concerning Wikipedia I understand that they are open to correcting their definitions. I learned this from another person who had pointed out that some of their definitions of 3 dimensional magic squares were inaccurate, and he made suggestions for corrections to them. I will have to correspond to him again to find if his redefinitions as a refinement were incorporated in Wiki's definition. Here's what Wiki says about Tesla's role in this definition with my comments in .
An early example of the bifilar coil can be seen in Nikola Tesla's United States patent 512,340 of 1894. Tesla explains that in some applications (which he does not specify)[Coil for Electromagnets] the self-inductance of a conventional coil is undesired and has to be neutralised by adding external capacitors.
[This is a very vague statement to say the least. Generally it is the "internal or self capacitance" of a coil that is undesired and not as here described as the self inductance. The relationship between internal capacity of a coil to the external capacity to be added to this coil in a resonant combination of course has a very prominent reduction in q factor. The % of this reduction in resonance can in fact be measured, I have directly measured many of the reductions myself and have the intention of posting a you-tube on the subject which is quite remarkable. Here I take a tesla primary cap value of 75 nf, and balance this with an equal inductive reactance value at 60 hz, which is a huge air core inductance. The ideal and actual q factors are compared, where it is then assumed that the also very large internal capacities of the inductors being employed are responsible for the reduction of the predicted resonance q factor.
An explanation for an old puzzle also seems present here, where when formerly presented did not seem to have a plausible conclusion, so representing the puzzle it goes something like this. Take a capacity and charge it up. Then add an equal capacity in parallel and discharge the voltage on the capacity so that it is now distributed across each capacity, reducing that voltage in two. C also changes becoming double. The energy storage term .5CV^2 then has both C and V increasing and decreasing in opposite magnitudes, but only the V side is exponential. This means that half the energy vanished when the capacitor shared its charge, so where did this go to? Ancient Chinese Secret? Take 64 or 8 squared equally long metallic segments and divide them into two, 32 segments to a side, and make a 2 dimensional plate capacity. Now use 6 squared or 36 segments and arrange them geometrically so that the same capacity determined by width of segments is done.
This is accomplished by making a single long length of segments and winding them in a fashion so that when the center point is broken, the winding pattern enables more then one side of the four sided conductor to be used for the internal capacity. Now this same capacity now contains an "internal inductance". Suppose we connect that coil at its midpoint with the external capacity which is the same value as its internal capacity. The predicted ideal Q factor to be made in series resonant voltage rise is already cut in half because the external capacity equals the inner. And the explanation for the dimunition of stored energy in this capacitive sharing begins to make more sense, it went into the magnetic field around the delivery wires.
The bifilar coil in this configuration has increased self-capacitance, thereby saving the cost of the capacitors.
[This scheme has never been sensibly employed. Many commentators have noted the differences in technology between our time and Tesla's and noted that this possibility never came into practical application.)
It is notable that this is not the kind of bifilar winding used in non-inductive wirewound resistors where the windings are wired anti-series to null out self-inductance.
[The purpose of internal capacity is to reduce the inductors natural resonant frequency. In accordance with this when an external capacity is added to that inductor, the balance of missing storage energy between two capacities in parallel is compensated for by the energy manifested in the magnetic field inherent in the conversion. This is only presented as a plausible theory made with analogies. Even a twisted turning capacitive pathway arranged in loops has inductance. A true nulling out of inductance by opposite directions of adjacent windings is impossible, and when this is applied in cases of fewer winds, the reduction of inductance can be shown to be much less then expected. Measuring the relative inductance of adjacent winds of large internal capacity Radio Shack MegaCable Spiral speaker wire flat braided windings by LCR meter will show this fact. Simply short one set and measure the inductance of the other adjacent set in both combinations of
mutual inductance. The adjacent spirals have almost perfect mutual inductance as will be seen by the inductance readings themselves.]
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