The bifilar pancake coil at its resonant frequency

[tinman]

I am in total agreement on the fact that the field collapse generates a current in the same direction of the input that built it. Could someone misinterpret a scope shot, seeing the voltage differential change at the time of input connect then disconnect as a current reversal? Maybe thats the bungle here?

Mags

I mentioned this some pages back,and i have seen this very mistake quite often before.


Brad

[tinman]

First I have to say that you simply interpreting that the coil is 10ohms gives your offering whatever outcome you are trying to convince others of.

Why cant the coil be 1ohm? or even .5ohm? Clearly he is not using wire that would have a 10ohm outcome. Looks to be 18 to 20ga, where 10ohms on that would mean he is using some resistive wire of sorts. Im only pointing that out as you used his 34uh coil and 49pf in your example. Saying or say, assuming his coil is 10ohm just by looking at it is a pretty big misstep in my opinion and using that 10ohm example changes what the actual outcome that you show and id say its totally misleading. Take another look at those coils. Did he say they were 10ohm? How many feet of wire do you think are on those coils? lets say that we can agree that the wire looks to be even 20ga. Do you still 'feel' that the resistance would be anything close to 10ohms? When you buy a cheap stereo system for the home and it comes with 2 10ft roles of say 20ga wire and the speaker is, now a days, 4ohm, what would 10ohms of resistance in the wire do to the outcome of the speaker output?

I just measured a 100ft roll of 18ga wire. 100ft!  1.4ohm     So would you say that his coils look like there is 700ft of wire there?

Now, if the coil did have 700ft of wire in order for the resistance to be 10ohm, then that completely changes the outcome of the inductance AND capacitance of which you are using in your example, big time. So you may need to rewrite you thesis on that one.


You say that he is feeding the coil 10w to keep it going at resonance. In my experience, at resonance the input is largely minimized. Where did you get that number??

Mags

I would say those coils would be lucky to be .10 ohm's.
Looks like plastic coated building wire to me.


Brad

[gyulasun]

Here is Conrad's video on his bifilar coil tests, Part 2  this is what MileHigh has referred to:
https://www.youtube.com/watch?v=spQ9yLdb7v4 

The coil parameters are clearly listed in the description text under the video, I quote:

"The following parameters are identical for both coils:

diameter of coil:     90 mm
number of wire turns:   30 monofilar, 15 bifilar
DC resistance:     0.4 Ohm
Inductance:     34 µH , measured with a LCR meter
phase angle in Z:     3 degrees, measured with a LCR meter"

So 0.4 Ohm DC resistance is involved.

Using MileHigh example of the 3.39 A RMS current in this coil, power loss would be 3.39^2 x 0.4 = 4.59 W instead of 114 W for a 10 Ohm coil. 
Once we use most parameters of a practical coil, why not use its exact DC resistance too?

Gyula 

[synchro1]

1 watt hour of power generates 1 Tesla of magnetic force in a coil of 1 Henry of inductance. How come no one could answer this question?

None of these "F" in inductance people can define "Negative Current" either!

Positive power goes in one electrode of the coil and out the other. When the power's interrupted, negative current leaves the coil in the same direction as the positive current did.

[tinman]

Wouldnt it be better if we look at the differences between the single wound pancake coil,and the bifiler pancake coil,and see if we can work out what those differences mean-or how they would change the operating characteristics of the coil.

Lets say that each coil(1x single wound,and one bifilar wound)has 100 turns in total,and we pulse each coil with a 100 volt potential across each coil--what ever frequency.

Now,as far as i know,the single wound coil would have 1 volt potential difference between each winding--although i believe that the potential difference between the windings at the center would be less than 1 volt,and increase between windings as you get toward the outer windings.


But,with the bifilar coil,the voltage between windings will always be 50 volts.
So,i see one coil with an uneven voltage between windings,and the other with an even voltage between windings.

So,what dose this mean ?
If each winding is seen as the two plates of a capacitor,and one coil dose not have an even voltage between winding,and the other dose-how would the stored capacitive energy stack up between the two?

Then there is the magnetic field--how would it differ between the two?
Dose the voltage potential between windings play any part in how the magnetic field will propagate around those windings,and that coil as a whole ?.


Brad