Calculating Magnetic Flux in Spool Coil with Air Gap - Formula and Example

Click For Summary

Discussion Overview

The discussion revolves around calculating the magnetic flux in a spool coil with an air gap, focusing on the appropriate formulas and the necessary parameters for the calculation. It includes elements of homework-related problem-solving and technical reasoning.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a formula for magnetic flux, phi = I * N / Rm, but expresses uncertainty about how to compute the current (I) needed for the calculation.
  • Another participant confirms the formula is correct but emphasizes the need for the correct reluctance and either the voltage or current in the spool.
  • A subsequent reply reiterates the importance of reluctance and suggests that the reluctance of the air gap is significantly greater than that of the core, indicating that the B-H characteristic may not be necessary.
  • There is a suggestion to assume a voltage of 24V for further calculations, but a participant questions how to proceed without knowing the current.
  • Participants discuss the necessity of obtaining the current to continue with the calculations, with one suggesting that it could be determined through various means.

Areas of Agreement / Disagreement

Participants generally agree on the need for current or voltage to compute magnetic flux, but there is no consensus on how to obtain the current or on the implications of the reluctance of the air gap versus the core.

Contextual Notes

The discussion highlights missing parameters, such as the current, and the dependence on assumptions regarding reluctance and voltage, which remain unresolved.

Mutaja
Messages
239
Reaction score
0

Homework Statement



The attached picture shows a spool coil on a iron core with an air gap measuring 2.5mm. The spool is coiled by 0.5mm2 with rho cu = 0.0175 Ωmm2 /m. The average winding diameter for the spool is 3.18cm.

Compute the magnetic flux in the spool.

attachment.php?attachmentid=67961&stc=1&d=1395681020.png

Homework Equations





The Attempt at a Solution



Using the equation: phi = I * N / Rm, I still miss I, and I have no idea how to compute it. Rm is the reluctance which I can get from a B-H characteristic - if that applies to this problem.

My first questions are these I guess: Is this the correct formula? If yes, how to I compute I?

Any feedback and help is as always greatly appreciated. Thanks.
 

Attachments

  • spool problem.png
    spool problem.png
    7.1 KB · Views: 598
Physics news on Phys.org
Your formula is fine but you need to use the correct reluctance.
You also need either the voltage or the current in the spool.

Hint: the reluctance of the air gap is >> reluctance of the rest of the core. Forget B-H of the core!
 
rude man said:
Your formula is fine but you need to use the correct reluctance.
You also need either the voltage or the current in the spool.

Hint: the reluctance of the air gap is >> reluctance of the rest of the core. Forget B-H of the core!

If I need the voltage or current, it would apprear it's missing from the problem - and I do apologize for that. But since you say I can use the voltage, how should I go about it if we set the voltage to 24V?
 
Per your equation, you need the current, right?
 
rude man said:
Per your equation, you need the current, right?

Yes, but the voltage is given at a later problem, so I figured why not just test it now as I'm not sure what to do. If I have the current, I would just need to plot it + find the correct reluctance to proceed.

I don't know though, it was just an idea.
 
?

get the current, by hook or by crook!
 

Similar threads

  • · Replies 13 ·
Replies
13
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
5
Views
3K
  • · Replies 15 ·
Replies
15
Views
7K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 20 ·
Replies
20
Views
3K