Inductances etc..

[ivconic]

Wire is approx. 0.27 with resin. Take it as 0.25mm ....without resin..

[Qiaozhi]

Now you made trivial mistake! Ahahahahah!

Inner radius for TX is 21cm and for RX is 15cm!

Not according to your own calculations. You stated that the TX diameter was 21cm, and the Nulling coil diameter was 15cm. Therefore the TX radius is 105mm and the Nulling coil radius is 75mm. These are the values I used in the coil calculator. You've been working too hard!

Also, the coil calculation includes the resin thickness.

[ivconic]

Oh man!
Something is wrong with your calculator!
I just checked it.
It calculated 70.5 turns for 6mH on 21cm former, using 0.25mm wire!
Not right! Not accurate!
I am sure my coil has 104 turns with wire (0.25 without resin...90% sure) and my brand new inductance meter reads 6.04mH!
Wires are not constrained tight...but also are not loose at all. It is former taken from scraped GTI coil. It has own cuttings, pretty convinient for wire windings. I actually do not need to constrain wires at all. Those are tight enough.
So... i think your calculator is not accurate...

Ignore this post. BS made by ivconic!

[ivconic]

Not according to your own calculations. You stated that the TX diameter was 21cm, and the Nulling coil diameter was 15cm. Therefore the TX radius is 105mm and the Nulling coil radius is 75mm. These are the values I used in the coil calculator. You've been working too hard!

Also, the coil calculation includes the resin thickness.

Sheeeeeeeeeeeeshhhhh!

Radius, RADIUSSS!
Y E S! You are RIGHT! Sorry!
Your calculator is ACCURATE!

[ivconic]

Yes...now this makes some sence!

[ivconic]

Ok..one more thing. Minor correction. Inner radius of Cancel coil is a bit larger than 75mm, cose there is RX coil below it...occupying few mm's! Let's adopt inner radius for Cancel coil as 77mm...

[Qiaozhi]

Sheeeeeeeeeeeeshhhhh!

Radius, RADIUSSS!
Y E S! You are RIGHT! Sorry!
Your calculator is ACCURATE!

In my calculations I have assumed that you will need to increase the TX inductance by the same value as the nulling coil. In practice this will not be the case, and the increase in turns may be much less than 9 turns. A lot depends on the amount of coupling between the TX and Nulling coils. I would start with 9 turns and gradually remove a turn at a time until the coil is correctly nulled.

[Qiaozhi]

Yes...now this makes some sence!

Hi Ivconic,

You are using an early version of the calculator that contained an error in the calculation. The inductance value is always too low. Please use the new version. I've attached it to this post.

[ivconic]

In my calculations I have assumed that you will need to increase the TX inductance by the same value as the nulling coil. In practice this will not be the case, and the increase in turns may be much less than 9 turns. A lot depends on the amount of coupling between the TX and Nulling coils. I would start with 9 turns and gradually remove a turn at a time until the coil is correctly nulled.

Thanks!
I will check that in practice tomorrow.
At least we moved from "dead" point!
Now i have something to rely on...

[ivconic]

Hi Ivconic,

You are using an early version of the calculator that contained an error in the calculation. The inductance value is always too low. Please use the new version. I've attached it to this post.

THANKS!

[WM6]

O

So... 2 coils, same axis, same plan, you may say same former holder (one coil is 15cm and another 21cm as on posted photo).
Wired in serie, in phase - giving one inductance,
Wired in serie, in antiphase - giving another inductance!

Regarding serial connection of coils some additional remark:

If we use one (1) coil with say 33 turns, we do not have only one inductor, but in fact 33 inductor with mutual coupled magnetic fields and serial connected. Even this claim is only simplified, cause in fact we have infinite number of serial connected inductors (remember we can easily check that even 2 cm of wire effect as measurable inductor at some frequencies).

So every coil have to be in principle treated as infinite number of inductors with mutual coupled magnetic fields and serial connected. In our calculations we usualy use only (optimal) simplified (depend on used frequency) approach if we take that 33 turns coil consist from only 33 serial connected inductor and not from infinite nr. of inductors.

From experience we know that smal tightens or small lose of turns in coil can results in remarcable changes in coil inductance. Cause turns (inductors) are mutual coupled by his magnetic fields, we can stated that level of mutual coupling play here a crucial role.

Unfortunately there are many mutually offsetting factors that influence to level of mutual coupling of inductors. Only by fixing some main of this factors to limited or fixed value we can get approach to calculations and formulas.

It is hard to imagine that for real needs this (e.g. your two coils problem) can be done without targeted lab testing, measurement and analitic work to fix influential variables. If we seek for simplified formula applicable in practice, of course, and not only for theoretical acrobatics.

[ivconic]

During make of all those coils so far, i noticed certain relations between number of turns and rise of inductance. It is cerain "nonlinear" progression.
Now easily calculatable by various calculators. Qiaozhi's calculator turned to be pretty accurate.
But just because of the reasons you explained above it is not possible to calculate (predict) exact no. of turns or inductance with 100% accuracy. There is always some jitter in calculations. I can live with that. It is easy to finaly correct it, once it was done pretty close...let's say to 95% accuracy.
We can say that part of a problem is solved thanks to calculator.
Now...the hardest part is to put it all togather and make it to work good.
Tough task.

For example i would take one White's coil i examined in the past;
my memory is blur now, i don't exactly remember all the facts, but
it was coil for White's Eagle IIc. I don't remember exact diammeter, but it was something like 25cm or close..
TX = 31 winding
RX= 396 winding
FB= 11 winding + 60cm free loop

At the time i had'nt any inductance meter. So i just made 2 "blind" copies of it..
It worked pretty good, considering my total "unawareness" of facts i am awared today!
But looking at that coil and considering number of turns i am sure that people from White's must had some calculations and already established rules by wich to project simillar coil. Free floating 60cm loop depose only about imperfectnes of those calculations and jitters that are present after calculation job is done. Never mind. Even with those lacks it is still something, good enough to start with. Starting this thread i wanted to learn at least that and to have some starting point.
We already calculated here relation between TX and Cancel coils no. of turns.
But i am affraid it will not solve the problem of coupling with RX coil...

[Qiaozhi]

Unfortunately there are many mutually offsetting factors that influence to level of mutual coupling of inductors. Only by fixing some main of this factors to limited or fixed value we can get approach to calculations and formulas.

It is hard to imagine that for real needs this (e.g. your two coils problem) can be done without targeted lab testing, measurement and analitic work to fix influential variables. If we seek for simplified formula applicable in practice, of course, and not only for theoretical acrobatics.

Agreed. There are always assumptions that need to be made when performing the initial calculations. For example, the Coil Calculator assumes a square cross-section to the windings, but this may not be the case in practice, particularly if the coil is wound onto a bobbin.

[ivconic]

Agreed. There are always assumptions that need to be made when performing the initial calculations. For example, the Coil Calculator assumes a square cross-section to the windings, but this may not be the case in practice, particularly if the coil is wound onto a bobbin.

In homemade arangement it is almost impossible to achieve square cross-section. Usually it is rounded and windings are mixed up more or less.

[Mikediver]

Calculation of mutual inductance

I hope that the solution is available. I have an old book concerned on the calculation of inductances for coils with different shapes. Also the solution of your problem is mentioned with the exact formulas (great pity, not so simple, but graphs from this book can help...). The only problem is russian language. The title is something like "Handbook for calculations of coil parameters", written by M.B.Nemcow and J.M.Schamayew. If you are still interested, can present copy of some pages or send you all book. File format is DejaVu.
Christmas greetings
Mike