# Inductor and Transformer Design Equations

## Main Question or Discussion Point

I thought it would be a good idea to write this down, all in one place, finally.
Any errors, or impovements needed? Should it be in gaussian units?

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## Answers and Replies

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stewartcs
Science Advisor
I thought it would be a good idea to write this down, all in one place, finally.
Any errors, or impovements needed? Should it be in gaussian units?
A .pdf would be better to thwart off any virus suspicions!

CS

berkeman
Mentor
I thought it would be a good idea to write this down, all in one place, finally.
Any errors, or impovements needed? Should it be in gaussian units?
What does this mean?

N – number of turns, Fingers
What's a Fingers? I don't think I've ever see units on the number of turns.

Overall looks good, very similar to my transformer/inductor crib sheet. It could use some diagrams showing flux and such, and should include the impedance transformation characteristic (goes by turns squared) of a transformer.

Do you do crib sheets for other subjects/topics as well? My crib sheet binder gets a lot of use.

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I would be very interested in seeing other engineer's crib sheets. My notebook is pretty bare (non-existent).

berkeman
Mentor
I would be very interested in seeing other engineer's crib sheets. My notebook is pretty bare (non-existent).
Interesting idea! Maybe scan our crib sheets and share them to generate ideas. I like that.

Let me work on that some.... Cool idea. Maybe a Crib Sheets sub-forum here at the PF...

A .pdf would be better to thwart off any virus suspicions!
CS
I was curious about that. How do you convert .doc to .pdf?

What does this mean?
Do you mean the Gaussian units? There are changes in some equations by a a couple factors.

I haven't done this in a while, maybe it was

$$v=N \frac{d\Phi}{dI}$$
that becomes
$$v=N \frac{d\Phi}{dI} \cdot 10^{-8}$$
in going from SI (kilogram-meter-seconds) to Gaussian units (essencially cgs. centimeter-gram-seconds)

I should check with some core manufactures to see what the prefered units are.

What's a Fingers? I don't think I've ever see units on the number of turns.

Overall looks good, very similar to my transformer/inductor crib sheet. It could use some diagrams showing flux and such, and should include the impedance transformation characteristic (goes by turns squared) of a transformer.

Do you do crib sheets for other subjects/topics as well? My crib sheet binder gets a lot of use.
I have notes buried within job folders, and never really concatenated them.
You know. One finger, two fingers, three fingers... That's how you count turns, right?

I think PF crib notes would be a very good idea. Would it be better to associate with each forum folder, or all in one place--under mirrored subfolders, maybe?

Oh, by the way, the Turns squared increase in inductance is in there--the last equation. So I'll label it as such.

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berkeman
Mentor
I was curious about that. How do you convert .doc to .pdf?
You can download a free conversion utility from PrimoPDF.com

It installs like a printer driver, so it shows up when you do "Print" from a software package (like Word or Excel) -- you choose to print to PrimoPDF instead of a printer, and it "prints" to a PDF file.

Thanks, berkeman. I got it loaded.

Bobbin cores and rod cores are difficult to solve, but a gapped core is not too difficult if you can guestimate the magnetic field fringent around the gap. But is the H field the same around the magnetic circuit given constant area. I'd been assuming it is in previous designs, with the results as expected, but is it true?

berkeman
Mentor
Thanks, berkeman. I got it loaded.

Bobbin cores and rod cores are difficult to solve, but a gapped core is not too difficult if you can guestimate the magnetic field fringent around the gap. But is the H field the same around the magnetic circuit given constant area. I'd been assuming it is in previous designs, with the results as expected, but is it true?
I believe so as well, as long as the area is constant.

I got this out of Wikipedia (Maxwell's Equations),

$$\oint_{\partial S}B \cdot dl = \mu_0 I_S$$

in the absense of electric fields, where

$$B=H\mu$$

I'll have to mull it over a little just to be sure it fits....

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