Re: Questioning the math Re: reluctance

<amdx@xxxxxxxxxxx> wrote:

The URL below adds iron to an air core solenoid to reduce
the reluctance and increase force.
The author calculates the reluctance of an air core as R1.
He then calculates the reluctance of two iron end plate washers as R2 and
R4.
Then the iron tube around the air core as R3.
He then adds R1+R2+R3+R4 for total reluctance.

It seems to me that R1 (the air core) is eliminated because it is
replaced (shunted) by the iron.
Can someone explain what I am missing here.
I understand at some point there will be an air gap,
but it will much smaller, I'll deal with that later.

http://www.oz.net/~coilgun/theory/externaliron.htm

Also in the section, "R2,R4: Finding Reluctance of a Flat Washer"
He goes through some calculus and gets,
Reluctance = 1/(2*pi*t*u)[ln(r2)-ln(r1)]


You need another pair of brackets to make the above correct:

Reluctance = (1/(2*pi*t*u))*[ln(r2)-ln(r1)]

= [ln(r2)-ln(r1)]/(2*pi*t*u)

He then reduces this to,
Reluctance = (ln(r2/r1)) / (2*pi*t*u)

I don't see this as correct,

Thanks Spehro, but I'm not on board yet.
I agree that,

(1/(2*pi*t*u))*[ln(r2)-ln(r1)] = [ln(r2)-ln(r1)]/(2*pi*t*u)

But, the author then reduces
[ln(r2)-ln(r1)]/(2*pi*t*u) to [ln(r2/r1)] / (2*pi*t*u)

When I plug numbers into these two I get different answers.
What am I missing?
My numbers, ln=2.718, r2=.6, r1=.5, t=.063, u=3500

Oh, and what about,
It seems to me that R1 (the air core) is eliminated because it is
replaced (shunted) by the iron.
As above.
Thank you,
Mike






.

Relevant Pages

  • Questioning the math Re: reluctance
    ... The URL below adds iron to an air core solenoid to reduce ... The author calculates the reluctance of an air core as R1. ... He then calculates the reluctance of two iron end plate washers as R2 and ...
    (sci.electronics.design)
  • Re: Questioning the math Re: reluctance
    ... The author calculates the reluctance of an air core as R1. ... Then the iron tube around the air core as R3. ... scientific calculator will allow you to ...
    (sci.electronics.design)
  • Re: Questioning the math Re: reluctance
    ... The author calculates the reluctance of an air core as R1. ... He then calculates the reluctance of two iron end plate washers as R2 and ... Then the iron tube around the air core as R3. ...
    (sci.electronics.design)
  • Re: Questioning the math Re: reluctance
    ... The author calculates the reluctance of an air core as R1. ... Then the iron tube around the air core as R3. ... scientific calculator will allow you to ...
    (sci.electronics.design)
  • Re: interesting DC-DC converter
    ... The toroidal core IS the "iron", on fast transitions created by the Q1+Q2 flip-flop it has much better eficiency then the traditional iron plates design. ... For air core you need frequencies to match, changing most of other components to respond to RF design. ... Reducing number of components is easy if you start designing from zero. ...
    (sci.electronics.design)
Loading