Re: Distributed capacitance effects Q?


"Richard Clark" <kb7qhc@xxxxxxxxxxx> wrote in message
news:v0c9339tduv6gjula9duhvt3fmc3h7e3th@xxxxxxxxxx
On Sun, 29 Apr 2007 06:52:17 -0500, "amdx" <amdx@xxxxxxxxxxx> wrote:

I agree with your assertion that distributed winding capacitance
degrades efficiency.
My thoughts about this are ;
Assume a 10 turn loop, between each turn there is a capacitance,
so, you have a complete circuit, (L,C,R) there is current
flowing through this circuit that is not flowing through the entire 10
turn loop. (this happens in the other 9 turns also)
I think these extra currents flowing that don't make the entire 10
turn circuit increase the losses.

Hi Mike,

Capacitance does not bring loss.

I'm not ready to give on that yet, but I could be convinced.
It seems I could add capacitors across turns of a coil and increase
circulating currents that would show as a lower Q. But I haven't
built a coil to test this.

Loss ALWAYS resides in Resistance and nothing else.

I agree, X/R=Q Lower Q means more loss.
(let's not get into radiation resistance right now)


Between you and Bill, there appears to be a fixation on the loopS
(emphasis on there being more than one). If you are going to blame
them (that emphasis on there being more than one), and try to tie it
to loss (that emphasis being naturally in Resistance, not
Capacitance); then it follows it is in the natural increase in
conductor Resistance that occurs when wires are spaced closer than 3
or 4 wire diameters to each other. When wires (or loops in this case)
are in close proximity, the magnetic field of the near wire (or loop
in this case, and each loop in proximity to the next) FORCES the
current in that loop to the surface of the wire - INCREASING that
conductor's Skin Resistance. Loss thus increases by proximity.
Capacitance does too, but that is merely a correlating factor.

Proximity effect could cause all of the additional losses.
Or it might just be part of the additional losses.

Why is it that when you get near self resonance of a coil the Q gets lower?
Note; to help clearify my question,
( as you get nearer and nearer resonance the capacitor you are using to tune
the inductor is getting smaller and smaller, and closer to equalling the
self
capacitance of the inductor)

Remember---Correlation is NOT causality.

If you measure reading skills in an elementary school you will find the
kids with big feet read better.

But then 5th graders usually have bigger feet than kindergarteners.

Thanks for the discussion____

Mike




.

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