Author Topic: The bifilar pancake coil at its resonant frequency (Read 573641 times)

MileHigh · « **Reply #870 on:** April 16, 2017, 12:41:07 AM »

Any experimenter that wants a quick and easy way to try out a cylindrical bifilar coil can simply buy a nice spool of fairly fine gauge speaker wire. All that you have to do is make the cross connection and voila, you have a nice machine-wound tightly-packed cylindrical bifilar coil to play with. Preferably it would be on a plastic spool and then you also have the ability to add a core if you want.

gyulasun · « **Reply #871 on:** April 16, 2017, 12:47:21 AM »

Quote from: MileHigh on April 16, 2017, 12:33:18 AM

....
You second question is strange, what's up with you? When you pulse a bifilar coil what happens? The response of the coil to a voltage pulse comes into play with an L/R time constant and all of that stuff that has been discussed in depth many times.

Well, MileHigh, can a square wave be considered pulsing a bifilar coil?

Conrad nicely demonstrates in his videos, especially in Part 1 https://www.youtube.com/watch?v=fC84W0PIZoE
when he switches from pure sine wave to square wave at 4 MHz, the bifilar coil nicely responds to
that wave much the same way as it does for the sine wave and of course the output response is sine wave as expected.
It gives pretty good response even to subharmonic (1/3) square wave excitation as well.

Is this still a strange question?

Gyula

TinselKoala · « **Reply #872 on:** April 16, 2017, 01:24:04 AM »

Quote from: MileHigh on April 16, 2017, 12:41:07 AM

Any experimenter that wants a quick and easy way to try out a cylindrical bifilar coil can simply buy a nice spool of fairly fine gauge speaker wire. All that you have to do is make the cross connection and voila, you have a nice machine-wound tightly-packed cylindrical bifilar coil to play with. Preferably it would be on a plastic spool and then you also have the ability to add a core if you want.

But you will get very very small interturn capacitance that way because the conductors are too far apart, even in the finest plastic insulated speaker wire. As you have pointed out, the interturn capacitance is small anyway, even with close-wound enamel insulated magnet wire.

ETA: I just saw Mags's result so maybe. That's a lot of capacitance he reports with his plastic-insulated wire with relatively large interconductor spacing. I get 2.19 nF with the bifilar pancake coil I showed in the first DC resistance test video (between disconnected files) which has 58+58 turns of #27 magnet wire and 661 microHenry when files are serially connected in the TBF manner. My calculator predicts a resonant frequency of 132 kHz for those values. We shall see, got to take dog to dogpark now.

Magluvin · « **Reply #873 on:** April 16, 2017, 01:57:11 AM »

Quote from: MileHigh on April 16, 2017, 12:20:41 AM

There are tons and tons and tons of mistakes made on this forum and sometimes some of them are completely and utterly idiotic. And almost all the time nobody says a single damn thing. I don't see you going after them and many times you are fully aware of them. So don't give me your nonsense and get my message loud and clear. You're are trying to preen and wank and say, "Look boys, I'm going to go after this guy and it's going to be sport." And I don't make "lots of mistakes." Get out of your BS spin zone.

Nobody wants your show, conduct yourself like a proper person.

Your coming up with 10ohm on conrads coils shows your inexperience with seeing such and making even an approximate determination of the resistance and it is far from showing that you are an authority in this area. Then you say that the difference between 10ohm and .4ohm doesnt make a difference anyway. Run the sim and see how long it takes for the ring to die down in each example. Its a large difference and your assumption of 10 ohms then posting all the formulas trying to show big issues to prove your view against others views, then yeah, it should be pointed out that you are not producing accurate info in your argument. That 10ohms wastes a lot of energy in the circuit at a very unnecessary and unrealistic rate.

So maybe, if i have to be blunt, just shedup.

Mags

TinselKoala · « **Reply #874 on:** April 16, 2017, 01:58:35 AM »

Quote from: synchro1 on April 15, 2017, 10:09:39 PM

@Tinselkoala,

Acting like you knew something and then set out to deceive everyone is a lot less flattering then just admitting to your ignorance.

There is nothing in my posts to you that is deceptive or even wrong. It is just too bad for you that the same cannot be said for you. Your deceptions and ignorance are right there in your history of posts, for everyone to see.

And I see that you are trying to push your nonsense on my YT channel as well. Thanks for the thumbs-downs by the way... now I know I'm reaching my Target Audience after all.

Magluvin · « **Reply #875 on:** April 16, 2017, 02:13:52 AM »

Quote from: TinselKoala on April 16, 2017, 01:24:04 AM

But you will get very very small interturn capacitance that way because the conductors are too far apart, even in the finest plastic insulated speaker wire. As you have pointed out, the interturn capacitance is small anyway, even with close-wound enamel insulated magnet wire.

ETA: I just saw Mags's result so maybe. That's a lot of capacitance he reports with his plastic-insulated wire with relatively large interconductor spacing. I get 2.19 nF with the bifilar pancake coil I showed in the first DC resistance test video (between disconnected files) which has 58+58 turns of #27 magnet wire and 661 microHenry when files are serially connected in the TBF manner. My calculator predicts a resonant frequency of 132 kHz for those values. We shall see, got to take dog to dogpark now.

I picked the wire for this some time ago when a RS store was going down for the count. was 29 bux and got 60%off so it was a no brainer. The flatness of the copper should give more surface area proximity than round wire per turn, that was my inspiration for going flat, to increase the capacitance. Like imagine say 1in wide copper tape or even wider. A nice increase in both capacitance and induction in a similar sized dia with a thin insulation layer between turns.

I feel good with the outcome of the capacitance and the inductance. I was also happy with the 85khz as it clearly shows a decent amount of inductance and capacitance to not only go lower than the mhz range, but i wasnt expecting below 100khz. How many ohms is the series total on your coil?

Mags

tinman · « **Reply #876 on:** April 16, 2017, 02:52:09 AM »

Quote from: Magluvin on April 15, 2017, 06:33:32 PM

Nice. Can you show a closeup of the wire? I was just talking about square wire. Also could you measure the capacitance between the windings? Separated of course not in series connection. Just interested to see what you get.with that wire with more close proximity surface area. Its gota be more than conrad had with the insulation and round wire. Not putting his effort down, just to see if you get better capacitance with what you got.

Mags

The wire used is from the primary of an old arc welder.
The wire is Ali-not copper.

So,wire size is 2mm x 3.5mm
I have the flat sides(3.5mm) wound against each other-->wire wound vertical you could say.

Values measured for bifilar coil

Capacitance value between the two windings is 1.22nF

Inductance value=EDIT=.06nH

Resistance(with series connection back in place)=.1 ohms

Picture of wire/remains of primary coil below.

Brad

tinman · « **Reply #877 on:** April 16, 2017, 02:57:21 AM »

So,when we say!self resonant frequency!,do we simply keep raising the frequency until maximum voltage amplitude is reached across the coil?

If so,who can calculate what mine should be,using the values given in my last post?.

Brad

Magluvin · « **Reply #878 on:** April 16, 2017, 03:13:53 AM »

Quote from: tinman on April 16, 2017, 02:52:09 AM

The wire used is from the primary of an old arc welder.
The wire is Ali-not copper.

So,wire size is 2mm x 3.5mm
I have the flat sides(3.5mm) wound against each other-->wire wound vertical you could say.

Values measured for bifilar coil

Capacitance value between the two windings is 1.22nF

Inductance value=.02nH

Resistance(with series connection back in place)=.1 ohms

Picture of wire/remains of primary coil below.

Brad

I get 1.02ghz.

Are you sure on that resistance of .1ohm? Just that I have 100ft of 14ga and it is .25ohm. Just really looks like some stout wire there and fewer turns than 55 or so i have.

Mags

Magluvin · « **Reply #879 on:** April 16, 2017, 03:18:49 AM »

Quote from: tinman on April 16, 2017, 02:57:21 AM

So,when we say!self resonant frequency!,do we simply keep raising the frequency until maximum voltage amplitude is reached across the coil?

If so,who can calculate what mine should be,using the values given in my last post?.

Brad

yeah you can do a freq sweep to find it. I use circuit sim to do simple tests like these to help find the freq with very good results. Thats how i found the 1.02ghz for u. it should be right on or close enough to find the area, just incase there is a slight discrepancy in a component value reading that could throw of the sim a bit if the values are not dead on. I like that sim. Simple stuff can be checked quick and reliably. The default circuit is an rlc so i just plug the values and apply power then disconnect and it rings and the res freq result is at the bottom right of the screen.

Mags

tinman · « **Reply #880 on:** April 16, 2017, 03:49:30 AM »

Quote from: Magluvin on April 16, 2017, 03:13:53 AM

I get 1.02ghz.

Are you sure on that resistance of .1ohm? Just that I have 100ft of 14ga and it is .25ohm. Just really looks like some stout wire there and fewer turns than 55 or so i have.

Mags

Thats the best i can measure Mags.

If i short my DMM leads together,i get .3 ohms,and across the coil,i get .4ohms.
My DMMs only have a resolution of .1 ohm

So how are we determining the self resonant frequency ?
Keep increasing the frequency until maximum voltage amplitude is reached across the coil?

Bellow is a pic of the two coils together .

Brad

Magluvin · « **Reply #881 on:** April 16, 2017, 03:50:12 AM »

Quote from: Magluvin on April 16, 2017, 03:13:53 AM

I get 1.02ghz.

Are you sure on that resistance of .1ohm? Just that I have 100ft of 14ga and it is .25ohm. Just really looks like some stout wire there and fewer turns than 55 or so i have.

Mags

When checking very low ohms and I consider 1 ohm pretty low, the connections of the meter leads to the wire really need a strong connection as a lack of solid contact can alter the true value to a higher reading than what it actually is.

Back it the early 90s I bought my first quality multimeter. Wavetek 2030. $329 back then and it seemed to be the only handheld at the time that could go to .01 accuracy. Well in amps and such there are resistors that go to that second decimal in accuracy and the best fluke couldnt read it to that accuracy back then. Still have it. It has a relative buttion that will record and subtract the test lead resistance to zero it out to 0.00 ohms leads shorted.

Other guys in the electronic repair shop didnt believe it would be accurate but IT showed them.

You can find the shorted IC or other component on a circuit board with many ICs and caps on a say 5v line on the board just by using the meter. To be able to read to .01ohm you will be able to track that part down without desoldering everything to isolate that bad part. Not many people know about that.

Mags

tinman · « **Reply #882 on:** April 16, 2017, 03:53:26 AM »

Quote from: Magluvin on April 16, 2017, 03:18:49 AM

yeah you can do a freq sweep to find it. I use circuit sim to do simple tests like these to help find the freq with very good results. Thats how i found the 1.02ghz for u. it should be right on or close enough to find the area, just incase there is a slight discrepancy in a component value reading that could throw of the sim a bit if the values are not dead on. I like that sim. Simple stuff can be checked quick and reliably. The default circuit is an rlc so i just plug the values and apply power then disconnect and it rings and the res freq result is at the bottom right of the screen.

Mags

Ah,see we were typing at the same time.

If it's 1.02GHz,then were screwed,as my SG only go's to 20 meg.

From last nights quick play,maximum voltage amplitude was reached at a far lower point-around 40KHz ,if i remember correctly.

Time for some testing. Back soon.

Brad

Magluvin · « **Reply #883 on:** April 16, 2017, 03:56:16 AM »

Quote from: tinman on April 16, 2017, 03:49:30 AM

Thats the best i can measure Mags.

If i short my DMM leads together,i get .3 ohms,and across the coil,i get .4ohms.
My DMMs only have a resolution of .1 ohm

So how are we determining the self resonant frequency ?
Keep increasing the frequency until maximum voltage amplitude is reached across the coil?

Bellow is a pic of the two coils together .

Brad

Yes the voltage on the coil will be highest at resonance.

Mags

Magluvin · « **Reply #884 on:** April 16, 2017, 04:06:32 AM »

Quote from: tinman on April 16, 2017, 03:53:26 AM

Ah,see we were typing at the same time.

If it's 1.02GHz,then were screwed,as my SG only go's to 20 meg.

From last nights quick play,maximum voltage amplitude was reached at a far lower point-around 40KHz ,if i remember correctly.

Time for some testing. Back soon.

Brad

Your inductance seems quite small compared to mine and TK, if that value is correct at .06nh where I have7nh and tk got around 1 or 2nh. On sim I may be wrong and it may be inaccurate at those freq or what ever. There are online calculators and you can plug in the values and get an answer. It does seem like a huge jump in freq in comparison so maybe we should try another calc to confirm that no.

Mags

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Author Topic: The bifilar pancake coil at its resonant frequency (Read 573641 times)

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