Parasitic capacitance in inductors

[Paul Burridge]

Hi,

Having read Chris Bowick's explanation of how these tiny capacitances
arise between the turns of a coil, I'm left wondering if it's the
whole story. Bowick states that they arise due to the resistance of
the inductor's wire. Albeit tiny, this resistance leads to minute
potential differences between turns, thereby giving rise to tiny
capacitances. Is that really the whole story? Do not phase differences
within the coil of the ac signal voltage make for far more potential
difference between turns? In particular as signal frequencies get
*very* high?

p.

 

[Kevin Aylward]

Hi,

Having read Chris Bowick's explanation of how these tiny capacitances
arise between the turns of a coil, I'm left wondering if it's the
whole story. Bowick states that they arise due to the resistance of
the inductor's wire.

Oh dear....

Albeit tiny, this resistance leads to minute

potential differences between turns, thereby giving rise to tiny
capacitances. Is that really the whole story?

It isn't any story at all. Seems like darkness to me. The potential
difference between coil loops is because loops are *inductors*!!!


Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

http://www.anasoft.co.uk/replicators/index.html

Understanding, is itself an emotion, i.e. a feeling.
Emotions or feelings can only be "understood" by
consciousness. "Understanding" consciousness can
therefore only be understood by consciousness itself,
therefore the "hard problem" of consciousness, is
intrinsically unsolvable.

Physics is proven incomplete, that is, no
understanding of the parts of a system can
explain all aspects of the whole of such system.

 

[Reg Edwards]

**** OLD WIVES' TALES ****

The self-capacitance of a multi-turn solenoid has little to do with the
capacitance between adjacent turns. All the little capacitances are in
series across the coil. Their resultant becomes very small as the number of
turns increases. And smaller still as the turns spacing increases and wire
diameter decreases.


Take a cylindrical coil former and cut it in half to form two smaller-length
cylinders. The effective self-capacitance across the winding is closely
related to the capacitance between the two cylinders.


Download in a few seconds coil-design program SOLNOID3 from website below
and run immediately.


Amongst other useful things SOLNOID3 calculates self-capacitance and
self-resonant frequency of an isolated coil.

----
............................................................
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
............................................................

 

[Paul Burridge]

**** OLD WIVES' TALES ****

The self-capacitance of a multi-turn solenoid has little to do with the
capacitance between adjacent turns. All the little capacitances are in
series across the coil. Their resultant becomes very small as the number of
turns increases. And smaller still as the turns spacing increases and wire
diameter decreases.

[snip]

Reg, let's assume for a moment that you know what you're talking
about. ;-)
Why did you post this info under a separate thread? It clearly relates
to the question I posed earlier about parasitic capacitances in
inductors, so why not just follow-up? "old wives tales" tells no one
anything about the content of your post. Fortunately I spotted it and
thanks for the info, anyway.

 

[Walter Harley]

Why did you post this info under a separate thread? It clearly relates
to the question I posed earlier about parasitic capacitances in
inductors, so why not just follow-up? "old wives tales" tells no one
anything about the content of your post. Fortunately I spotted it and
thanks for the info, anyway.

What newsreader are you using? Mine (Outlook Express) shows Reg's post as
being part of the same thread, with the subject line changed.

I believe it is the "References" header that permits a newsreader to support
this. (It's been 13 years since I wrote a newsreader program, so I don't
remember for sure.) "Thread" and subject line.

 

[Reg Edwards]

"old wives tales" tells no one

anything about the content of your post.

...................................................

It tells you it was an old wife ready for ducking who palmed you off with a
load of rubbish in the first place. And you accepted it without question as
being gospel truth.

Doing things this way is more educational. It sharpens your wits. Clears
out the old-wives' nonsense. The circumstances under which the new
information has been knocked in will greatly assist your memory to retain
it. I'm sure you'll agree.

Havn't you downloaded the program yet? Get a move on!

 

[John Popelish]

Hi,

Having read Chris Bowick's explanation of how these tiny capacitances
arise between the turns of a coil, I'm left wondering if it's the
whole story. Bowick states that they arise due to the resistance of
the inductor's wire. Albeit tiny, this resistance leads to minute
potential differences between turns, thereby giving rise to tiny
capacitances. Is that really the whole story? Do not phase differences
within the coil of the ac signal voltage make for far more potential
difference between turns? In particular as signal frequencies get
*very* high?

In a coil of any reasonable Q (inductive reactance dominating
resistance) the main voltage source that moves charge around in the
inter turn capacitance is the inductive voltage drop, not the
resistance. Even super conducting coils have a self resonant
frequency.

 

[John Popelish]

**** OLD WIVES' TALES ****

The self-capacitance of a multi-turn solenoid has little to do with the
capacitance between adjacent turns. All the little capacitances are in
series across the coil. Their resultant becomes very small as the number of
turns increases. And smaller still as the turns spacing increases and wire
diameter decreases.

Take a cylindrical coil former and cut it in half to form two smaller-length
cylinders. The effective self-capacitance across the winding is closely
related to the capacitance between the two cylinders.

Download in a few seconds coil-design program SOLNOID3 from website below
and run immediately.

Amongst other useful things SOLNOID3 calculates self-capacitance and
self-resonant frequency of an isolated coil.

I agree that the adjacent turn capacitance is a small part of the
total effective capacitance across a multi layer coil. The
capacitance between the first turn of one layer and the last turn of
the next layer has lots more voltage across it, and the capacitance
between the start and end leads has the most voltage across it.
Crossing back to the same start end for each layer cuts the inter
layer capacitance by about half, and keeping the start and end leads
short and as far as possible from each other also helps. A bit if
extra insulation between layers (especially low permitivity material
like teflon or air) also helps.

 

[Paul Burridge]

In a coil of any reasonable Q (inductive reactance dominating
resistance) the main voltage source that moves charge around in the
inter turn capacitance is the inductive voltage drop, not the
resistance. Even super conducting coils have a self resonant
frequency.

Can you define "inductive voltage drop"?

 

[Paul Burridge]

It tells you it was an old wife ready for ducking who palmed you off with a
load of rubbish in the first place. And you accepted it without question as
being gospel truth.

I beg your pardon, Reg??? On the contrary I posted a question on
Bowick's explanation immediately after reading it. It didn't sound
right to me. Tomorrow I'll dig up the exact quote from his book. It's
odd he should screw up on something as simple as this as most of what
he writes is very accurate and informative.

Doing things this way is more educational. It sharpens your wits. Clears
out the old-wives' nonsense. The circumstances under which the new
information has been knocked in will greatly assist your memory to retain
it. I'm sure you'll agree.

Havn't you downloaded the program yet? Get a move on!

Already got it, thanks.

But it doesn't answer my original question re Bowick's explanation...

 

[John Popelish]

Can you define "inductive voltage drop?

V=L*(di/dt)

 

[Tim Auton]

What newsreader are you using? Mine (Outlook Express) shows Reg's post as
being part of the same thread, with the subject line changed.

My newsreader (Agent, Paul's using Free Agent) can tell what
newsreader somebody is using by displaying the headers

It is a known (to me, anyway) problem that Agent does this, it's
rather irritating. Oooh, I just looked at the preferences and you can
turn it off.

Options - General Preferences - Message List, untick "Enable Threading
by Subject" and "Start a new thread when follow-up subject changes".
Then to force it to re-calculate its threads, right click on the group
and change it to sort messages by something other than thread, then
change it back - et voila! Perhaps restarting or getting new message
headers would also do the re-threading, I don't know.

I believe it is the "References" header that permits a newsreader to support
this. (It's been 13 years since I wrote a newsreader program, so I don't
remember for sure.) "Thread" and subject line.

It is the references header, which Agent otherwise deals with properly
(preserving it, using it to spot cross-posts etc).


Tim

 

[Paul Burridge]

V=L*(di/dt)

The actual quote from Bowick's book (at page 15) is:
"Real-World Inductors
"As we have discovered in preverous section of this chaptre, there is
not perfect component and inductors are certainly no exception. As a
matter of fact, of the components we have discussed, the inductor is
probably the component most prone to very drastic changes over
frequency.... As previously dicussed, whenever we bring two conductors
into close proximity but separated by a dielectric and place a voltage
differential between the two, we form a capactitor. Thus if any wire
resistance at all exists, a voltage drop (even though very minute)
will occcur between the widings, and small capacitors will be formed.
This effect is called distributed capacitance."

So this explanation is definitely wrong, then?

 

[Kevin Aylward]

The actual quote from Bowick's book (at page 15) is:
"Real-World Inductors
"As we have discovered in preverous section of this chaptre, there is
not perfect component and inductors are certainly no exception. As a
matter of fact, of the components we have discussed, the inductor is
probably the component most prone to very drastic changes over
frequency.... As previously dicussed, whenever we bring two conductors
into close proximity but separated by a dielectric and place a voltage
differential between the two, we form a capactitor. Thus if any wire
resistance at all exists, a voltage drop (even though very minute)
will occcur between the widings, and small capacitors will be formed.
This effect is called distributed capacitance."

So this explanation is definitely wrong, then?

Yep, as much as it refers to resistance. The resistance is usually
insignificant. Its inductance that matters. That's were the volts drop
is V=2.pi.f.L.I

It seems to be the rule, that people who write books don't know what
their talking about. So, you can see why I haven't wrote a book yet.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

http://www.anasoft.co.uk/replicators/index.html

Understanding, is itself an emotion, i.e. a feeling.
Emotions or feelings can only be "understood" by
consciousness. "Understanding" consciousness can
therefore only be understood by consciousness itself,
therefore the "hard problem" of consciousness, is
intrinsically unsolvable.

Physics is proven incomplete, that is, no
understanding of the parts of a system can
explain all aspects of the whole of such system.

 

[Ban]

Kevin Aylward wrote:
||
|| It seems to be the rule, that people who write books don't know what
|| their talking about. So, you can see why I haven't wrote a book yet.
||
|| Kevin Aylward

Kevin,
with your awful English you will definetly need John Woodgate as a
proofreader then.

ciao Ban

 

[John Woodgate]

I read in sci.electronics.design that Paul Burridge
[email protected]>) about 'Parasitic capacitance in inductors', on Tue, 18 Nov
2003:

So this explanation is definitely wrong, then?

No, it's true, but it's not the whole truth. As has been explained, the
inductive reactance of each turn contributes more than the resistance in
the frequency range for which the inductor is suitable, and capacitances
exist in real inductors, other than single-layer, that are larger than
the inter-turn capacitances. These add to the *self-capacitance* but are
not part of the uniformly *distributed capacitance*.

 

[John Woodgate]

I read in sci.electronics.design that Kevin Aylward <kevindotaylwardEXTR
[email protected]> wrote (in <[email protected]
..net>) about 'Parasitic capacitance in inductors', on Tue, 18 Nov 2003:

So, you can see why I haven't wrote a book yet.

Tell us when you've writ it. (;-)

 

[Kevin Aylward]

I read in sci.electronics.design that Paul Burridge


No, it's true, but it's not the whole truth.

Its no where near the truth. Its utter gibberish. For the resistance of
the coil to matter, it must have a Q around or less than 1. As I said,
any capacitance effects can only occur because of the difference in
potential due to inductive impedance, not resistance.


Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

http://www.anasoft.co.uk/replicators/index.html

Understanding, is itself an emotion, i.e. a feeling.
Emotions or feelings can only be "understood" by
consciousness. "Understanding" consciousness can
therefore only be understood by consciousness itself,
therefore the "hard problem" of consciousness, is
intrinsically unsolvable.

Physics is proven incomplete, that is, no
understanding of the parts of a system can
explain all aspects of the whole of such system.

 

[Kevin Aylward]

Kevin,
with your awful English you will definetly need John Woodgate as a

Get real, you have no f'ing idea what your talking about. There is f'all
wrong with my English.


Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

http://www.anasoft.co.uk/replicators/index.html

Understanding, is itself an emotion, i.e. a feeling.
Emotions or feelings can only be "understood" by
consciousness. "Understanding" consciousness can
therefore only be understood by consciousness itself,
therefore the "hard problem" of consciousness, is
intrinsically unsolvable.

Physics is proven incomplete, that is, no
understanding of the parts of a system can
explain all aspects of the whole of such system.

 

[John Popelish]

The actual quote from Bowick's book (at page 15) is:
"Real-World Inductors
"As we have discovered in preverous section of this chaptre, there is
not perfect component and inductors are certainly no exception. As a
matter of fact, of the components we have discussed, the inductor is
probably the component most prone to very drastic changes over
frequency.... As previously dicussed, whenever we bring two conductors
into close proximity but separated by a dielectric and place a voltage
differential between the two, we form a capactitor. Thus if any wire
resistance at all exists, a voltage drop (even though very minute)
will occcur between the widings, and small capacitors will be formed.
This effect is called distributed capacitance."

So this explanation is definitely wrong, then?

It is a perfect explanation of the frequency limit of wire wound
resistors.

I have almost never found a technical reference book that contained no
errors. I am just glad I have not been given the responsibility to
create a zero error book on anything.