Tesla's "COIL FOR ELECTRO-MAGNETS".

[fritz]

(...) if we want it to turn on fast (current to flow as quick as possible) then we need to look at cancelling it's self inductance in order for it to turn on quicker. Wouldn't we ?

As already pointed out - I think the technical relevance of that tesla patent is about "these" types of coils - and it´s no practical approach for quick switching due to the ohmic losses in such coil.
Its all about about no cap and less isolation distance needed, I suppose.

The usual way for a "quick turn on" is to use high voltage and current control.
If you want a stepper motor with high speed and torque you typically use for example a "3V"  motor and operate it with 48Volts.
The voltage for such motors is rated for DC losses at 3Volts. If you have a pulsed driver with 48Volts in chopper mode - and limit the current+adjust the chopper timings to keep the ohmic losses within the same range as operated with "pulsed 3V DC".
A "3V" motor has lower DC resistance and  lower inductivity than a motor rated for higher voltages (DC).

So I would design towards low inductance, low DC resistance, high voltage and smart switching/chopping.
For half-bridge designs, I would use a "snubber" to limit "turning off" time.
With an H bridge - you could feed the energy back into the caps of the powersupply.


rgds.

[synchro1]

(http://www.overunity.com/Themes/default/images/post/xx.gif)Re: Magnetic Overunity Motor Design« Reply #4 on: August 09, 2012, 03:48:10 AM »Quote
Update #1:

Wound the coils in bifilar manner; windings are parallel.  Each coil is 1000 turns, 9.1 Ohms.  My goal was to create the same number of Ampere turns with less resistance and lowered voltage.  What I discovered is that I was way wrong about how it would actually work.  So this is for all those aspiring folks out there: Powering the 2 coils in parallel DOES NOT double the turns just because you have two coils wound together, it only allows more current flow at the same voltage because of the lowered resistance.  Winding bifilar coils and connecting them in parallel is the same as using a larger gauge wire.

With this letdown under my belt there is a silver lining, sorta.  Powering them in series does make a stronger electromagnet.  Not sure why yet but it does.  This assertion is based on force measurements I made between the bifilar coil and a single strand wound coil.  And according to Tesla's patent, it allows extra storage of "magnetic" field energy (2X when compared to a single strand coil of the equivalent turns),!

[gyulasun]

As already pointed out - I think the technical relevance of that tesla patent is about "these" types of coils - and it´s no practical approach for quick switching due to the ohmic losses in such coil.
Its all about about no cap and less isolation distance needed, I suppose.
.....

Hi Fritz,

I agree with most what you mentioned in your above post, except for what I quoted in bold. The reason is that Tesla wrote in his patent:

"I have found that in every coil there exists a certain relation between its self-induction and capacity (i.e. capacitance) that permits, a current of given frequency and potential to pass through it with no other opposition than that of ohmic resistance, or, in other words, as though it possessed no self-induction."

So he drove the series bifilar coil with an AC current whose frequency was the same as the self resonant frequency of his series bifilar coil and this way the usual inductive reactance every coil manifests (away from resonance)  did not oppose the initial input current: the input current was determined only by the coil's ohmic resistance in his circuit.  So the advantage of his coil construction was two fold: he did not have to use a dedicated HV capacitor for tuning the coil and the other advantage was the input current did reach its maximum value possible without delay, dictated by the ohmic coil wire resistance only. This latter is not the case for coils operated (i.e. pulsed) below their own resonance frequency: current can only increasy exponantially during the 5*L/R time duration.

rgds,  Gyula

[gyulasun]

(http://www.overunity.com/Themes/default/images/post/xx.gif)Re: Magnetic Overunity Motor Design« Reply #4 on: August 09, 2012, 03:48:10 AM »Quote
Update #1:

Wound the coils in bifilar manner; windings are parallel.  Each coil is 1000 turns, 9.1 Ohms.  My goal was to create the same number of Ampere turns with less resistance and lowered voltage.  What I discovered is that I was way wrong about how it would actually work.  So this is for all those aspiring folks out there: Powering the 2 coils in parallel DOES NOT double the turns just because you have two coils wound together, it only allows more current flow at the same voltage because of the lowered resistance.  Winding bifilar coils and connecting them in parallel is the same as using a larger gauge wire.

With this letdown under my belt there is a silver lining, sorta.  Powering them in series does make a stronger electromagnet.  Not sure why yet but it does.  This assertion is based on force measurements I made between the bifilar coil and a single strand wound coil.  And according to Tesla's patent, it allows extra storage of "magnetic" field energy (2X when compared to a single strand coil of the equivalent turns),!

Hi synchro1,

Unfortunately I have to deduce from his posts that when travin69 changed the coils to bifilar wound types his single wound coils earlier had also 1000 turns??  Because if the single coils had 1000 turns and he wound the bifilar coils with also 1000 turns to create the same number of Amper turns, then it is obvious he got stronger electromagnet when powering the bifilar coil in series!  2 x 1000 turns makes stronger electromagnet than 1 x 1000 turns. 
(When powering the 2 x 1000 turns in parallel, he noticed it was the same as using a thicker wire to make the coil. First he wished to make the bifilar coil with comparable Amper turns to the single coil, hence the 1000 turns in parallel bifilar.)

Gyula

[synchro1]

                   "Based on the force equation for electromagnets and coils, force increases based on the face area of the poles"

                               This force equation might help explain one advantage of Tesla's pancake design for electromagnets..

He goes on to describe his experiment to TK:


Tinsel:

I wound two seperate wires simultaneously parallel to each other.  What I was led to believe (stupid me) was that if I powered them in parallel, I could add each coils windings together and halve the current.  BKGD: Each coil is 200 ft of 26AWG wire and makes about 1100 turns or so on the coil.  This in fact is false and to double the ampere turns, i have to double the amperage.  Since I am trying to keep my I2R losses to a min, I am just going to wind them IAW Tesla's patent.  Currently, they are about 0.925" long.  I want to get them down under 0.75" if possible.  I have heard that as the windings get further away from the core, the outer windings aren't as coupled to the core.  I have not seen this actually printed in any of the books I have read. 

After some recent research, I have discovered that some coils are wound with different gauge wire and wound more like a transformer with windings on top of windings.  I would like to put 22 AWG wire on first, say 300 turns, then finish it off with 26 AWG wire wound on top, like 700 turns.  If I am not mistaken, the outer coil's magnetic field should concentrate the inner field and result in a more uniform magnetic field.  This method is done at many of the research labs to get magnetic fields in excess of 30 Teslas