# Parasitic capacitance in inductors

Discussion in 'Electronic Design' started by Paul Burridge, Nov 17, 2003.

1. ### John LarkinGuest

If Bowick thinks that the distributed capacitance of a coil is caused
by its resistance, then he is a lumped element.

John

2. ### pat dot lawler att verizon dott nneettGuest

"Thus if any wire _impedance_ at all exists, a voltage drop (even
though very minute) will occur between the windings, ..."

3. ### John WoodgateGuest

I read in sci.electronics.design that John Larkin <[email protected]
4ax.com>) about 'Parasitic capacitance in inductors', on Thu, 20 Nov
2003:
He doesn't say that. What he effectively says is that even at
arbitrarily low frequencies the resistance of each turn produces a
voltage across the inter-turn capacitance. This is true, but it is far
from the whole story, which is what I commented initially.

In sci.electronics.design, pat dot lawler att verizon dott nneett
wrote:
And since its an inductor conducting an AC current, such impedance
DOES exist (or more correctly it always exists, the inductive
reactance part is greater than zero for ac and is zero for DC).
For an alternating current, inductance is an impedance (a general
term) or a reactance (a more specific term) - there will be a voltage
drop between adjacent windings, even if the resistance is zero. In
practical inductors, at the usual frequencies of interest, the
inductive reactance accounts for much more of the voltage difference
between windings than does the resistance.

5. ### Paul BurridgeGuest

It's not though, is it? The propagation velocity in wire is somewhat
slower than that in air. That's why one has to multiply it by the
'free space correction factor' - something in the region of 97% of
light speed, IIRC.

6. ### Paul BurridgeGuest

Bowick actually refers to this parasitic capacitance between turns as
"distributed". I'm still waiting for the Panel to come to a definitive
conclusion as to whether Bowick's explantation, which I have
reproduced here verbatim, is accurate or not. Is the quote given from
his book correct or not?

7. ### Paul BurridgeGuest

And well worth it, I'm sure. Reg, do you have any programs in your
remarkable collection that tackle the problems of maximising radiated
power of (far from) non-ideal antennas for clandestine operation?

8. ### John PopelishGuest

It is not close enough to right to be useful.

9. ### Reg EdwardsGuest

========================

You don't need a program. Just turn up the wick.

========================
========================

Winny was disappointed, eh?

Reg, G4FGQ ;o)

10. ### John WoodgateGuest

I read in sci.electronics.design that Paul Burridge
>) about 'Parasitic capacitance in inductors', on Fri, 21 Nov
2003:
I repeat that it's true, but it's not the WHOLE truth. The per-turn
resistance DOES create a voltage across the inter-turn capacitance, but
in the frequency range where the per-turn inductive reactance is
comparable with or far exceeds the per-turn resistance, the voltage due
to the inductive reactance also appears across the inter-turn
capacitance.

The inter-turn capacitance is there whether there is any current in the
inductor or not. So where the voltage across it comes from is a question
quite separate from that about the existence of the capacitance.

11. ### Fred BloggsGuest

We're not talking about that kind of "distributed." The distributed
component I'm talking about dimensionally spans a significant fraction
of a wavelength of the operating frequency.

12. ### Paul BurridgeGuest

Yeah, but then the final trannie goes 'pop' due to the appalling
mismatch caused by a (necessarily) folded-up ariel.

13. ### Rich GriseGuest

The resistance doesn't have anyhting to do with the capacitance,
except when they're interacting. The capacitance is because
there are two conductors separated by an insulator. It just
sits there, so to speak.

Cheers!
Rich

14. ### Paul BurridgeGuest

So are you saying there doesn't need to be any potential difference to
arise between the turns for there to be an inter-turn capacitance?

15. ### John WoodgateGuest

I read in sci.electronics.design that Paul Burridge
>) about 'Parasitic capacitance in inductors', on Wed, 26 Nov
2003:
Indeed. An uncharged capacitor doesn't cease to exist.

16. ### Paul BurridgeGuest

I think that's a metaphysical question that more properly belongs to
the realm of philosophy, John.

17. ### John WoodgateGuest

I read in sci.electronics.design that Paul Burridge
>) about 'Parasitic capacitance in inductors', on Thu, 27 Nov
2003:
I checked before making such a controversial statement. I short-
circuited some of the capacitors in my stock, and they didn't disappear.

18. ### Paul BurridgeGuest

Ah, but shorted them at what frequency?
;->

19. ### John WoodgateGuest

I read in sci.electronics.design that Paul Burridge
>) about 'Parasitic capacitance in inductors', on Thu, 27 Nov
2003:
About one every 20 seconds, I think.

20. ### Paul BurridgeGuest

Very good. It obviously took you a while to think that one up.