Looking for formula to calculate gapped inductor

Discussion in 'Electronic Design' started by [email protected], Aug 15, 2007.

1. Guest

Could anyone give me the formula for calculating the value of gapped
inductor? I don't want to mess with theory, all I need is the equation
and preferably in SI units. Thanks for helping ^_^

2. Fred BartoliGuest

Le Wed, 15 Aug 2007 05:09:36 -0700, w2kwong a Ã©crit:

Could you give me the money your customer is paying you.
I don't want to mess with marketing and such, all I need is the bank
transfer, and preferably in Euros. Thanks for paying ^_^

3. MooseFETGuest

I can't give you SI units but you can convert. A gapped inductor is

Y = 43.2 + 1.7*G + 53*W

Where:
Y = How much it is in US dollars
G = The number of faces that you need to grind
W = The weight in pounds

I hope this helps.

5. D from BCGuest

I take paypal

D from BC

6. RST Engineering \(jw\)Guest

What the hell is a gapped inductor?

Jim

You really should "mess with theory" at some point...

But in the interest of answering your question... it's easy to compute the
inductance of a gapped core vs. an ungapped core; the result is:

L_gapped/L_ungapped = L_e/mu_r / (L_e/mu_r + L_gap)

....where L_e is the effective length that the flux traverses, mu_r is the
relative permeability of the of the core, and L_gap is the length of the gap.
L_gap, of course, has to have the same units as L_e.

Notice that for large values of mu_r, the gap length alone starts to dictate
the entire inductance.

---Joel

8. Bob MyersGuest

Ummm...for instance, an inductor made on a
toroidal or similar "closed" core shape, but with a
slot cut through the core material. Think of a

Bob M.

9. RST Engineering \(jw\)Guest

Iiiim, sorry. I call those gapped core. I thought he was winding an
inductor with spaces between the windings.

Jim

10. Bob MyersGuest

Yeah, "gapped core" would be more common, but I'm
pretty sure that's what the OP meant.

Bob M.

11. Guest

Mates may I apologies for my poor expression, since English is not my
I'm still a UG student and don't get money for doing my thesis
project. Instead I myself 'm paying thousand bucks to buy my own
equipments, blown chips etc, and it's unlikely that I will be able to
claim these cost from supervisor.

12. ChairmanOfTheBoredGuest

You're an idiot. Almost ALL core manufacturers provide gapped cores
per customer spec.

I hope you get help.

13. ChairmanOfTheBoredGuest

You have to actually possess the capacity to provide the required
services before you would deserve a dime...

Unless, of course, you are a doctor... Then you can shuffle folks in
and out of your office all day, taking only vital signs, and billing
insurance companies out the ass for near zero actual performed services.

14. MooseFETGuest

I already knew that this was your latest nym. You didn't have to
prove it with yet another example of your stupidity, but here we have
such a fine example that I feel I should respond and fully quote what
I said and how you responded so that others may enjoy a good laugh at
your expense. Even those who have kill filed you, I am sure, will
have a good giggle. You really didn't get it did you?

15. MooseFETGuest

Beware that at large sizes of gaps, this equation is inaccurate. It
assumes that the lines of force pass as straight lines from one face
to another.

16. ChairmanOfTheBoredGuest

"Large" is a fairly ambiguous choice of terms here.

Yes, good point. Another one I forgot to mention is that with cores that have
mating surfaces (e.g., pot cores) the tiny spaces between the two touching
halves can be enough such that there's sometimes already a non-negligible gap
that makes the mu_r listed on the data sheet more of an "effective" value
rather than the true bulk material value. This of course causes the equation
listed to be somewhat inaccurate as well.

Hopefully this guy measures the inductance he ends up with prior to using the
device in a circuit...

18. TraverGuest

Toroids actually have a "gap" as well but it is distributed though the
core material without actually seeing a physical gap. With non -
toriods like E-E cores for example, you need to gap the cores by
putting a thin spacer in between the two Es or grinding down the
center leg. This gives you the ability to chose the gap. Toriods come
in a fixed gap with various discrete values.

19. Terry GivenGuest

if, and only if, its a distributed-gap core, e.g. iron powder, koolmu etc.

for ferrite toroids, this statement is entirely incorrect.

With non -
conversely, this is only true for non-distributed-gap cores e.g.
ferrite, metglass etc.

Cheers
Terry