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Author Topic: The bifilar pancake coil at its resonant frequency  (Read 567656 times)

Vortex1

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1245 on: April 30, 2017, 05:28:50 AM »
My response video to Russ's response video.


https://www.youtube.com/watch?v=nHqs72bYyUw

Good job on the response to response video Brad.

More informative, and tells the truth of the matter.  :)

Keep up the good work!

Regards

P.S. might be interesting to put some tiny matched incandescent lamps in place of the 100 ohm resistors and drive the circuit harder....just for fun.  ;)

That would give you an  eyeball current and power indication / balance in the loop.
Three would be even better, one on the right, the middle and the left. Just don't connect the scope or the balance will be upset.
 

tinman

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1246 on: April 30, 2017, 06:41:18 AM »
Good job on the response to response video Brad.

More informative, and tells the truth of the matter.  :)

Keep up the good work!

Regards

P.S. might be interesting to put some tiny matched incandescent lamps in place of the 100 ohm resistors and drive the circuit harder....just for fun.  ;)

That would give you an  eyeball current and power indication / balance in the loop.
Three would be even better, one on the right, the middle and the left. Just don't connect the scope or the balance will be upset.

Hi Vortex

I tried the smallest grain of wheat bulbs i have,and the SG just dose not have the power to light them up.


Brad

tinman

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1247 on: April 30, 2017, 06:42:55 AM »
Below are the scope shots with associated scope placings as requested by TK,with the widened time scale.
I have also included the math trace for each,which is showing the result of V x I.

Anyone seeing a pattern forming here with all these tests ?


Brad

TinselKoala

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1248 on: April 30, 2017, 06:45:04 AM »
Those tiny incandescent lamps are called "grain of wheat" bulbs and I am happy--- and rather astonished--- to see that they are still available in this day of the ubiquitous LED.

http://www.ebay.com/sch/?_nkw=grain%20of%20wheat%20lamps


Magluvin

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1249 on: April 30, 2017, 08:16:31 AM »
By using a TBF coil with more turns he could have brought the frequency range of interest down to within the range of his current probes. And as we know, as I have demonstrated,  you don't need a pancake coil to show the effect, it works just fine with TBF solenoid coils too, which are _much_ easier to wind. And it even works with monofilar coils, but less strongly since they have less distributed capacitance.

Russ demonstrated the phase shift which we all know is there and which will occur in _any_ inductive coil whether flat, solenoidal, Tesla bifilar, or monofilar wound.
It's too bad he didn't also demonstrate the power analysis software of his scope. He probably needed the current probes active and deskewed to be able to do that.

So the appropriate way to test this circuit is to measure the Vdrop across each resistor separately, without making groundloops by misconnecting the voltage probe references. In fact I do this using the same scope channel and probe, by moving the probe from resistor to resistor, so as to be absolutely sure not to introduce ground loops (and also I know for a fact that my FG's outputs are isolated from ground; is Russ's FG also isolated in this way? Many aren't.) This will give the actual power dissipated in the resistors, and no correction for phase need be applied in this purely resistive case.  Then one measures the power relationships in the inductive portions separately, and using the Phase Shift between voltage and current in the inductors themselves, one can calculate the Real power, Reactive Power, and Apparent Power in those mostly non-dissipative inductors. Here is where Russ's Power Analysis software in his scope would come in handy.
 

Hey T and Brad

So when measuring R1 we can calculate the input power as it is showing input currents whether they are the result of the interaction with the coils and the other resistor or not. Then we have R2 showing more dissipated power than what we see on the input. Whether we have looked at the coils independently or not, with just the 2 resistors we are seeing something more than in on R2.  Is that correct?

Wondering something. I know its probably silly, but what if we took out the 100ohm R1 and put a 50ohm at each end instead.  I dont know why yet exactly but when we have the differences in coil voltages, rms, pp, there seems to be an off balance set in.  Like if we did the 50 on each end, would we have balance? Possibly the 1 winding compared to the other may have differences, but,  anyway.  Cool stuff.

Mags

TinselKoala

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1250 on: April 30, 2017, 09:12:48 AM »
Brad there is seemingly something wrong with at least some of the readings in your scopeshots above. Have you changed the FG's output between shots? Look at the first and second shots. I hope we can agree that the CH2 VRMS reading across R1 only, should be the same in both these shots unless the FG's output has changed!

And looking at shots 2 and 3, one would expect the phase shift between CH1 and CH2 to be the same since, presumably, the inductance of the half-coils are the same or nearly the same in the TBF winding. Yet the phase shift shown on #2 is almost perfectly 90 degrees, but on #3 it is quite a bit less,  more like 45 degrees.

Can your scope provide a measurement value for the phase shift?

So I'm wondering "what gives" here with these scopeshots.

tinman

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1251 on: April 30, 2017, 09:16:10 AM »
Hey T and Brad





Mags

Quote
So when measuring R1 we can calculate the input power as it is showing input currents whether they are the result of the interaction with the coils and the other resistor or not. Then we have R2 showing more dissipated power than what we see on the input. Whether we have looked at the coils independently or not, with just the 2 resistors we are seeing something more than in on R2.  Is that correct?

No
Measuring the voltage drop across a resistor with a known value,will give you the input current to the circuit as a whole,and the dissipated power of that resistor.

Quote
Wondering something. I know its probably silly, but what if we took out the 100ohm R1 and put a 50ohm at each end instead.  I dont know why yet exactly but when we have the differences in coil voltages, rms, pp, there seems to be an off balance set in.  Like if we did the 50 on each end, would we have balance? Possibly the 1 winding compared to the other may have differences, but,  anyway.  Cool stuff.

I would suspect that each 50 ohm resistor would show the same value,and the center resistor would still show a higher value.

I believe that the extra energy is within the second coil(as per my diagram),and i believe i have found a way to tap into it  ;)

I just carried out a test,and i can dissipate more power using the coil,than my function generator can deliver to the load it self. ;)

Brad

tinman

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1252 on: April 30, 2017, 09:29:01 AM »


 

Can your scope provide a measurement value for the phase shift?

So I'm wondering "what gives" here with these scopeshots.

Quote
Brad there is seemingly something wrong with at least some of the readings in your scopeshots above. Have you changed the FG's output between shots? Look at the first and second shots. I hope we can agree that the CH2 VRMS reading across R1 only, should be the same in both these shots unless the FG's output has changed!

The only thing i changed as i went through each step,was the voltage P/D value on the scope,so as to keep each waveform close to the top and bottom of the screen.
The FG was not touched for each test point.
I do not know why the current value changed,when i shifted CH1's probe to the end of L1

Quote
And looking at shots 2 and 3, one would expect the phase shift between CH1 and CH2 to be the same since, presumably, the inductance of the half-coils are the same or nearly the same in the TBF winding. Yet the phase shift shown on #2 is almost perfectly 90 degrees, but on #3 it is quite a bit less,  more like 45 degrees.

Once again,please note the value difference in the VPD,while the time scale remains the same.
Other than that,nothing else was changed during the test.
I am happy to shoot a video showing this,if you like.

But what is the math trace telling you?


Brad

hoptoad

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1253 on: April 30, 2017, 10:06:19 AM »
snip...
I just carried out a test,and i can dissipate more power using the coil,than my function generator can deliver to the load it self. ;)
Brad
Worms! Gotta love em, hard to grasp, slippery as they can be.

TinselKoala

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1254 on: April 30, 2017, 10:24:25 AM »
Brad, I've done the same thing with my Tesla Bifilar solenoid coil, just because it's easier to work with than the pancake coil. Here are my three scopeshots that correspond to your three shots above. Using 10 ohm resistors just as you have done and connected to FG and scope exactly as you have done.

Note that the CH2 RMS measurement is practically the same for #1 and #2, as it should be since the probe and ground reference positions haven't changed. And also note that the phase shifts in #2 and #3 are also the same, as it should be since both half-coils have essentially the same inductance.

I don't much like using the fine-tuning controls on the V/div scales to make the traces the same height on the screen, but since you did that, so did I.

My scope, thankfully, will do Measurements on the Math trace so I've shown the Average value of the Math in all three cases. I'm too coffee-deficient at the moment to be able to tell if these are valid values or what they might mean, though.

TinselKoala

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1255 on: April 30, 2017, 12:30:06 PM »
Please note that the Rigol has known bugs in its RMS measurement calculations so I wouldn't trust those figures. I probably shouldn't have included them in the scopeshots, I should have put p-p values instead so that we humans could calculate the RMS values from them instead of relying on the scope's math for that.


Meanwhile, trusting TinMan's Atten scope's RMS measurements... I performed some calculations using the values from his three scopeshots above. I posted these on OUR but I'm repeating the post here for discussion.

___________________________________

Ok.... it would still be better if your scope could compute the phase shift itself. But in your First shot, if we take the rms current through R1 (CH2) as 0.0618V/10R = 0.0062 Arms as the current being supplied to the system, and the voltage drop across the whole circuit (CH1), and estimate the phase shift as 72 degrees, we then calculate the total input average power as
P = Vrms x Irms x cos (72 degrees)
P = 6.60 x 0.0062 x 0.309
P = 0.0126 W or 12.6 mW

And if we calculate the power dissipated in R1 as
P = Vrms2/R
P = 0.0712/10
P = 0.0005 W

And the power dissipated in R2 as
P = Vrms2/R
P = 0.3482/10
P = 0.0121 W

So we get the total power dissipated in the resistors as
0.0005 + 0.0121 = 0.0126 W or 12.6 mW.

Coincidence?

This result is very sensitive to the Phase Shift in part 1, so we really need a good measurement of that. 
 

tinman

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1256 on: April 30, 2017, 12:41:27 PM »
Brad, I've done the same thing with my Tesla Bifilar solenoid coil, just because it's easier to work with than the pancake coil. Here are my three scopeshots that correspond to your three shots above. Using 10 ohm resistors just as you have done and connected to FG and scope exactly as you have done.

Note that the CH2 RMS measurement is practically the same for #1 and #2, as it should be since the probe and ground reference positions haven't changed. And also note that the phase shifts in #2 and #3 are also the same, as it should be since both half-coils have essentially the same inductance.

I don't much like using the fine-tuning controls on the V/div scales to make the traces the same height on the screen, but since you did that, so did I.

My scope, thankfully, will do Measurements on the Math trace so I've shown the Average value of the Math in all three cases. I'm too coffee-deficient at the moment to be able to tell if these are valid values or what they might mean, though.

So your total P/in is 6.99mW ?
dissipated power in R1&L1 is 4.27mW ?
And in R2& L2 it is 3.81mW ?
So P/in is 6.99mW
P/out is 8.08mW ?

Also,i think my scope is toasted,or has a hickup there some where.


Brad

TinselKoala

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1257 on: April 30, 2017, 01:16:50 PM »
So your total P/in is 6.99mW ?
dissipated power in R1&L1 is 4.27mW ?
And in R2& L2 it is 3.81mW ?
So P/in is 6.99mW
P/out is 8.08mW ?

Also,i think my scope is toasted,or has a hickup there some where.


Brad

No, the scope isn't calculating the Math value correctly for some reason. And not trusting the Vrms values, I went ahead and did the P-P x 0.3535 to get RMS values of my own...and they are quite close to the RMS values reported by my scope so maybe the RMS bug has been fixed in the latest firmware revision which I loaded a few weeks ago. But the Math averages shown on the scope are definitely still wrong.

Repeating the same calculations on my values that I did for yours, here's what it looks like.

Total input power is Vrms x Irms x Cos (82.7 degrees) = 4.86 x 0.0193 x 0.127 = 0.0119 W or 11.9 mW.
Power dissipated in R1 is P = I2R = 0.01932 x 10 = 0.003725 W
Power dissipated in R2 is P = I2R = 0.021872 x 10 = 0.004783 W
Total power dissipated in resistors is then 0.00851 W or 8.51 mW.
BUT... my coil has a lot of turns of fine wire and its DC resistance is 10.3 ohms total. So we have to include the power dissipated in that resistance as well.
Power dissipated in coil's DC resistance is P = I2R = 0.01932 x 10.3 = 0.003837 W or 3.84 mW.

And that brings our total dissipation to 0.01235 W or 12.35 mW  -- compared to our input calculation of 11.9 mW. This is within rounding and measurement error of being equal.  COP=1.04 is not significantly greater than 1.0 considering the measurement uncertainties and roundings.

nelsonrochaa

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1258 on: April 30, 2017, 01:19:08 PM »

Also,i think my scope is toasted,or has a hickup there some where.


Brad

Try join to "church" , maybe you earn a new one, and your envy and of some fellows could become in happiness.


Nelson Rocha

TinselKoala

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Re: The bifilar pancake coil at its resonant frequency
« Reply #1259 on: April 30, 2017, 01:28:56 PM »
Repeating the above calculations and taking the scope's reported RMS values and phase shift as "exact", along with a more precise measurement of the DC coil resistance as 10.4 ohms, I get

Total Input Power = 0.011846 W or 11.85 mW.
Total dissipated power in R1+R2+Rcoil = 0.01178 W or 11.78 mW.

Rounding to three significant digits we have 11.8 mW in = 11.8 mW out.