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## Discussion board help and admin topics => Half Baked Ideas => Topic started by: raburgeson on March 03, 2006, 01:53:27 AM

Title: Inductive kick
Post by: raburgeson on March 03, 2006, 01:53:27 AM
Would like to here from you guys on this. What delivers the most powerful inductive kick
an electro-magnet, coil, some special inductor? I ask about circuits that don't require
super cooling or have other unique needs of course.
Title: Re: Inductive kick
Post by: Elvis Oswald on March 03, 2006, 02:46:20 AM
A simple experiment with a 9v battery and a nail and some wire will show you that bifilar winding gives you a stronger magnet than just regular winding.  :)

And... a tank circuit resonating with the source will produce a "shitload" of inductance in the core of the coil.

Title: Re: Inductive kick
Post by: magnetoelastic on March 03, 2006, 03:32:43 AM
A bifilar winding denotes two, tightly coupled windings traveling the same direction.  If the two windings are connected in parallel, you get actually less inductance than if you used a single winding with the same number of turns, because each of the two windings is less tightly coupled to the ferromagnetic core.  If the two windings are connected in series, it is the same effect as if you had a single winding with double the number of turns - which in effect you are creating.  If the two windings are connected anti-parallel, you get far less inductance that either of the other two conditions, because the fields of the two windings tend to oppose.
Bifilar windings are of particular utility in constructing transformers, not inductors.
Title: Re: Inductive kick
Post by: magnetoelastic on March 03, 2006, 03:37:54 AM
To obtain the greatest inductive 'kick, you need the following:  Maximum inductance, maximum capacity for stored energy (from a gapped core), and a laminated core construction to minimize eddy currents when the current is interrupted.  Look for an old radio filter choke - like 10 henries at 100 mA is a common value.  A 9volt battery across that will lay you on your tail.  Fair Radio Sales should have them.
Title: Re: Inductive kick
Post by: Elvis Oswald on March 03, 2006, 07:09:45 AM
Well... if you take two nails...
wind one with 100 turns of wire...
then wind the other with 50 turns using two wires together...
and connect them in series -
so that you have basically two 50 turn coils...
in series but interleaved...
and yes this is a bifilar winding...
Connect each of them to a battery and see how much each will pick up.

You will see that the bifilar winding has more magnetic strength.

This is an experiment that you can easily duplicate so that we will all be on the same page.  :)

Does this not prove that a bifilar winding - in series - will store more energy - using the same source and the same number of turns??
Title: Re: Inductive kick
Post by: magnetoelastic on March 03, 2006, 03:37:48 PM
Conceding that I have actually never verified this assertion, I tested this idea.  I have a selection of ferrite rods, used for portable AM radio antennas.  The part I selected was 0.5" dia, and 4" long.  I first wound it with 200 continuous turns of 30 AWG, kynar insulated wire.  This covered all but about 1/4 of the core on each end.  It took 27 feet of wire, including 4" free for each end.  I measured the DC resistance to be 2.7 ohms.  I measured the inductance to be 1.70 mH.  Connecting a 1K resistor in series, and using a 9 volt battery as a source, (measured 8.8 volts under load),  I measured a 6.2 Gauss magnetic field directly off the end of the rod.

I then stripped off the windings, cut the wire in half, and re-wound the coil in bifilar fashion.  Then I connected the end of winding #1 to the beginning of winding #2.  The measured resistance was 2.7 ohms, the measured inductance was 1.71 mH, and the magnetic field with the 9 volt battery attached was 6.2 Gauss.

To my satisfaction, the two configurations are essentially equivalent.
Title: Re: Inductive kick
Post by: Elvis Oswald on March 03, 2006, 08:41:50 PM
That is better than a paperclip test, eh?  :)

I won't be picky about the core material.  Harder metal makes a better magnet... but you would expect the same ratio (1:1) regardless of the material used.

The only explaination must be that my wire was not insulated - neither was the nail.  So - eddy currents?  Stray capacitance between the turns?   Either way it is a poor design and one gain probably equals a loss of something else.

Thanks for taking the time to test it  :)
Title: Re: Inductive kick
Post by: magnetoelastic on March 03, 2006, 09:28:58 PM
Choice of core materials matters - some.  For a rod shaped electromagnet, if the core is the same size, you get just about the same strength flux output regardless of whether the core is iron, steel, or ferrite.

If you are making a permanent magnet, you want hard steel - carbon or nickel steel, preferably carburized.  The same mechanism that makes steel hard also tends to keep the domains oriented, resisting demagnetization.

If you want to make an inductor, you want soft steel - annealed, for the same reason.  This keeps hysteresis losses low.

More speciallized applications require speciallized core materials, of course.
Title: Re: Inductive kick
Post by: magnetoelastic on March 03, 2006, 09:39:28 PM
Elvis, there is a really great book on inductor design, free for download at

http://www.pmillett.com/Books/Lee%201955%20Electronic%20Transformers%20and%20Circuits.pdf

written by Reuben Lee, one of my old Westinghouse buddies.  It is clearly written, and very helpful in understanding these matters.
Title: Re: Inductive kick
Post by: Elvis Oswald on March 03, 2006, 10:03:41 PM
ty
Title: Re: Inductive kick
Post by: raburgeson on March 04, 2006, 03:03:24 AM
I have to be the lousiest at asking questions, Is there a specific core material that will maximize the kick. Like a transformer core is made from a material composed to reduce lag by charging and discharging a magnetic field quickly. What I ment to ask is is there so special magnetic core out there or something that is more efficient at producing the kick than a normal inductor? I know it's my fault on the question so I thank you all for your time so far. I am looking for max current and I know that means shortest kick duration.
Title: Re: Inductive kick
Post by: magnetoelastic on March 04, 2006, 05:48:42 AM
Like my old profs used to say, no such thing as a stupid question.

A core to maximize inductive kick would be of laminated shell or tape core construction, of the highest-saturation-flux-density material available.  If cost is no object, one of the amorphous permalloy-based alloys is the way to go.  This will allow you to store the highest energy into the core, and lose the least in hysteresis.

Title: Re: Inductive kick
Post by: raburgeson on March 06, 2006, 04:36:55 PM