EMRFD Message Archive 11672

Message Date From Subject
11672 2015-09-26 12:48:10 bob_ledoux Question about Toroid Winding Protocol
The recommendation is tribal knowledge:  "Wind the toroid in a single layer.  Leave about 30 degrees of the core uncovered.  Spread or squeeze the turns to adjust the inductance."

How important is this protocol?

Who originated it? 

Was it intended to ensure consistent performance by builders without measurement tools?

With the low cost meters available should we just wind, even multiple layers, to a specified value?

bob-N7SUR


11673 2015-09-26 12:59:52 Lasse Moell Re: Question about Toroid Winding Protocol
Winding multiple layers would affect Q, and guess the "formula" you have would probably give max Q.

/Lasse

26 september 2015 21:48:09 +02:00, bobledoux@proaxis.com [emrfd] skrev:

 

The recommendation is tribal knowledge:  "Wind the toroid in a single layer.  Leave about 30 degrees of the core uncovered.  Spread or squeeze the turns to adjust the inductance."

How important is this protocol?

Who originated it? 

Was it intended to ensure consistent performance by builders without measurement tools?

With the low cost meters available should we just wind, even multiple layers, to a specified value?

bob-N7SUR





11674 2015-09-26 13:03:05 kb1ckt Re: Question about Toroid Winding Protocol
I would sweep well above target freq. Multiple layers will increase parasitic capacitance, which may mean something in the circuit which uses it. I would think loss would go up also.

Adjusting turns spacing should not change inductance as much affect the distributed capacitance.

But it can't hurt to try. Only costs a bit of wire. I have been trying to make some baluns and ununs here, and it has been fun, if not slow, finding what isn't working.

shawn kb1ckt

Sent from my iPad

11676 2015-09-26 15:26:49 kerrypwr Re: Question about Toroid Winding Protocol
This is an interesting paper that shows clearly the inter-winding capacitance of single-layer & multi-layer toroid windings;

www.powerelectronics.com/mag/508PET22.pdf


(Whilst not relevant to this discussion, the way in which the authors suggest that more turns can be accommodated on a toroid is rather astonishing; not one for the home-brewer  :)  ).

I think, from memory, that it was W1FB who promulgated the "30 degree rule" in the amateur community; it's in his Design Notebook and later in a 1996 CQ article .  He may have done some tests.  It was probably known previously in the professional world.

If you want a headache-producing analysis of winding capacitance, Snelling provides one in "Soft Ferrites".

Kerry VK2TIL.
11677 2015-09-26 16:06:30 bob_ledoux Re: Question about Toroid Winding Protocol
DeMaw was a very bright fellow.  His "Design Notebook" was my first reference for toroid techniques.

The article, referenced above, argues that multiple layer coils display more parasitic capacitance.  The same is true if the space between start and end of winding is not preserved.

It also discusses "wire forming" technology that varies the wire diameter over its length.  This permits the wire to be thinner on the inside of the toroid core and thicker on the outside, thus permitting more turns to be applied.  This preserves the wire area that permits higher current flow.  I don't want to go there.  A bigger toroid is fine with me.

bob-N7SUR
11678 2015-09-26 16:53:12 chuck adams Re: Question about Toroid Winding Protocol


11685 2015-09-27 14:16:54 Brooke Clarke Re: Question about Toroid Winding Protocol
Hi:

Capacitance depends not only on the mechanical configuration but also on the voltage between the plates.
For example if you wind a toroid leaving a gap of 30 degrees you can think of the capacitance as the series connection of N capacitors (where N is the number of turns).  Note this is correct since the voltage across each capacitor is V/N (where V is the terminal voltage).

But now consider winding two layers, still leaving a 30 degree gap.  The capacitance of the first turn to the last turn has the full terminal voltage across it and that capacitance is in parallel with the rest of the inter winding capacitance.  So not only are all the intermediate capacitance values added but they are much stronger because they have much more voltage across them.

Not mentioned so far is the fill factor of the toroid core.  The first layer is almost completely filled with core.  It can't be 100% because of any coating
11686 2015-09-27 17:04:45 afu Re: Question about Toroid Winding Protocol
Hi,

since when depends capacitance on the vltage between the plates ??

Is this a new knowledge from agricultural sience ??


Herbet


Am 27.09.2015 22:16, schrieb Brooke Clarke brooke@pacific.net [emrfd]:
 

Hi:

Capacitance depends not only on the mechanical configuration but also on the voltage between the plates.
For example if you wind a toroid leaving a gap of 30 degrees you can think of the capacitance as the series connection of N capacitors (where N is the number of turns).  Note this is correct since the voltage across each capacitor is V/N (where V is the terminal voltage).

But now consider winding two layers, still leaving a 30 degree gap.  The capacitance of the first turn to the last turn has the full terminal voltage across it and that capacitance is in parallel with the rest of the inter winding capacitance.  So not only are all the intermediate capacitance values added but they are much stronger because they have much more voltage across them.

Not mentioned so far is the fill factor of the toroid core.  The first layer is almost completely filled with core.  It can't be 100% because of any coating

11687 2015-09-27 18:52:18 vasilyivanenko Re: Question about Toroid Winding Protocol

Hi Bob

 

I think the 30 degree recommendation might rank as 70% folklore for typical Hams making stuff @ HF.
Doug DeMaw’s  most important point was to spread the windings over the toroid and not in a tight bunch leaving much of the donut uncovered.


I once examined the 30 degree gap assertion -- since to me at least, it did not make sense.


I swept some coils looking at SRF, resonator Q and calculated parallel C.   The only thing that changed significantly when measuring equal inductance coils that had or did not contain a 30 degree gap was the SRF.


One 906 nH toroid coil exhibited a an SRF of 326 MHz with about a 35 degree gap. The SRF is made up of the parallel resonance of the 906 nH inductance and the sum of the inter-winding capacitance and the capacitance generated between the gap of the first and last winding [gap capacitance].  I calculated the SRF parallel C at 0.27 pF.   For sure, the C went up a bit with no gap and the SRF went down.


Since the SRF of our typical ~1 - 5 uH inductors lays well above HF, a 30-40 degree versus a 0 degree gap makes no practical difference.  Sometimes we need to fill a toroid! 


I would love to see other people’s data.


Best!

11688 2015-09-27 21:29:47 John Maxwell Re: Question about Toroid Winding Protocol
11689 2015-09-27 22:01:13 K5ESS Re: Question about Toroid Winding Protocol

Count me in on wanting to see a technical explanation for this claim.

Mike K5ESS

 

11690 2015-09-27 22:08:16 K5ESS Re: Question about Toroid Winding Protocol

Maybe we should give Brooke a little bit of slack and assume he meant the MEDIUM between the plates rather than the VOLTAGE between the plates.  Yes?  No?

Mike K5ESS

 

11691 2015-09-28 03:26:32 kb1ckt Re: Question about Toroid Winding Protocol
Class II capacitors have a voltage dependency.
Should not apply here, to a torroid winding question, bit a good number of capacitors do have all sorts of curves.

shawn kb1ckt

Sent from my iPad

11695 2015-09-28 05:46:47 kb1gmx Re: Question about Toroid Winding Protocol
This aught to be good.

Actually I do know of exceptions, I'll leave it as not this one.

Allison
11696 2015-09-28 09:05:33 afu Re: Question about Toroid Winding Protocol
Hi Shawn,

you are out of context..... here the theme was toroide winding and and the influence of
the geometrical way to wind and the capacitance of the coil and not some material
properties of capacitors, else we should also talk about the ability of interaction of
capacitor voltage and mechanical deformation well known as piezostriction..
but we should not do that in this context because there is no direct connection
of these effects with a toroid winding strategie !

Herbert



Am 28.09.2015 11:26, schrieb kb1ckt@yahoo.com [emrfd]:
 
Class II capacitors have a voltage dependency.
Should not apply here, to a torroid winding question, bit a good number of capacitors do have all sorts of curves.

shawn kb1ckt

Sent from my iPad

11697 2015-09-28 10:07:14 Brooke Clarke Re: Question about Toroid Winding Protocol
Hi:

You are correct I misspoke.  The capacitance is not a function of the voltage across the capacitor.

The equivalent circuit of a single layer coil, for determining it's capacitance, looks like a series string of capacitors so the overall capacitance is the turn to turn capacitance divided by N (the number of turns).   Ctotal = Cturn-to-turn/N

If you draw out a circuit diagram for the capacitance of a double layer coil it will look like a ladder with the two terminals on the left.  The very first element in the circuit will be a shunt cap that's the top to bottom turn to turn capacitance followed by two adjacent series capacitors followed by another top to bottom turn to turn capacitance and so on.  For this case were the first and last turns are adjacent to each other the coil capacitance is much higher than N times the turn to turn capacitance.

This is why when you look at electronics made prior to the advent of ICs you will see many mechanical types of coils.  For example by "bank winding" where a multilayer coil is wound in such a way that the terminals are at opposite ends the self capacity is much lower, for example see the top loopstick photo at:
http://www.prc68.com/I/Loop.shtml
Click on photo to see larger image, click again if cursor is (+).

Another example is the old 2.5 mH choke where there there are a few basket woven coils spaced out on a rod.  The two terminals are on opposite ends of the final product.  You can get the same effect by using bobbins where there are more than one slot.  When each slot is filled with wire then the next slot is filled and so on.  The terminals are far from each other. 

A similar thing could be done on a toroid where you need multiple layers but also want low self capacity.  Bank winding or using septums made of thin plastic would allow keeping the terminals in series.

One implicati
11704 2015-09-29 11:48:23 afu Re: Question about Toroid Winding Protocol
Hi,

this way of winding a toroid s interesting for industrial
production and for non real RF products. By this way of
winding, the self capacitance of the coil will "explode,
because the windings will have over the half or more
than a turn only the distance of the varnish ( isolation)
between the turns, instead of only two round profiles
side by side. The flattened wire of that patented way of
winding is definitely not usefull for "real" RF !

Herbert


Am 27.09.2015 00:53, schrieb chuck adams chuck.adams.k7qo@gmail.com [emrfd]: