Building an Inductor

Discussion in 'General Electronics Chat' started by Xeeshan Qureshi, Apr 15, 2009.

1. Xeeshan Qureshi Thread Starter Member

Jan 13, 2009
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Hi,
can someone tell me how i can build an inductor of 25H. It is not available in the market.
I don't have an LCR meter (an inductance meter precisely), is there any other method to check the 25H i'll build...?
thanx

Oct 22, 2008
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3. steveb Senior Member

Jul 3, 2008
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What is the current level and operating frequency?

4. KL7AJ AAC Fanatic!

Nov 4, 2008
2,181
410

The simplest way to do this is with a high permeability ferrite toroidal core. These are available in different permeabilities from Amidon Electronics, Palomar Engineers, and a few others. There are also pot-core ferrites available...a little easier to wind with small wire, but quite a bit more expensive.

eric

5. Wendy Moderator

Mar 24, 2008
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I was planning on starting a thread to measure inductance. The easiest way I can think of is a simple sine wave generator, say around 100 - 1Khz. Most decent DVMs can measure the AC at these frequencies. So you put a resistor in series with the inductor, measure the input AC value, measure the AC value across the inductor, the ohm value in the coil, frequency, and plug the values into reluctance math (don't forget the vector for phase shift).

A high end DVM will measure frequency, and AC values, the rest is math.

Basically it was a continuation of this thread.

Last edited: Apr 15, 2009
6. wollybyte Member

Apr 5, 2009
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are you sure its 25H
or is it 25uH

Apr 5, 2008
18,882
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Hello,

What is the use of the VERY large inductor?
Is it really 25 H ?
Or is it 25 mH or 25 μH or even 25 nH?

Greetings,
Bertus

8. thatoneguy AAC Fanatic!

Feb 19, 2009
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An FT-240 type W Ferrite Core would need 1352 turns of 40 Gauge wire (larger gauge wire won't fit), length of wire is 225 ft. Max current = 1mA

$FT-240-W \rightarrow A_{\small{L}}= \frac{13960mH}{(1000 x N)^{\tiny2}$

--ETA: 25H is very huge, and would block nearly everything other than DC, with very little current ability. Although a Laminiated iron core, such as in a power transformer, may allow larger wire, the inductor would be over 10 pounds to have any kind of current handling ability.

--ETA Again, for fun, I tried an air core: About 280 lbs of 18 Gauge wire, in a muli-layer spiral with 87,000 turns, needing 12.5 miles of wire, with the end result 3 feet thick, and 27 feet in diameter. This should explain why most posts are asking if MilliHenries or Microhenries was intended.

Last edited: Apr 15, 2009
9. SgtWookie Expert

Jul 17, 2007
22,202
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Gee, are you sure about those air core numbers, thatoneguy?
AWG 20 magnet wire on a 3" wide 12" diameter bobbin, 6765 turns, 92 turns/layer, 73.4 layers, avg diameter 14.4", outside diameter 16.8", 25,487 feet of wire, 259 Ohms resistance. Just over 25H inductance.

10. thatoneguy AAC Fanatic!

Feb 19, 2009
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That's for a spiral wound, thin/fat disc reltative to diameter, rather than a long coil. I may have missed a decimal point on my slide rule though.

11. hgmjr Retired Moderator

Jan 28, 2005
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I think a potcore may be a more DIY friendly inductor solution for this large an inductor. I look forward to the OP's explanation for the need for such a large valued inductor.

hgmjr

12. KL7AJ AAC Fanatic!

Nov 4, 2008
2,181
410

We regularly used coils of this range of inductance for ELF/ULF detection for ionospheric research

http://www.vlf.it/matteobruna/ULF_Induction-Coil.htm

Commercial versions run around \$10,000, but you can roll your own a lot cheaper!

Eric

13. Bernard AAC Fanatic!

Aug 7, 2008
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Not impossible, I have a 10H , 85Ω, 300mA choke by Triad. Abuot 12 lb. About 4X4X5 in. Wonder what inducteace of microwave trabsformer 2000 V winding?

14. srm_creator New Member

Apr 17, 2006
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what level of current?
what level of DC resistance do you need?
what kind of signal are you planning to apply to it?

Without these information, everything else is speculation

15. Xeeshan Qureshi Thread Starter Member

Jan 13, 2009
14
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ooooopssss
you are right
250mH and 500mH are what i require... not 25H

operating frequency 830-890MHz (1200MHz peak boosted).

Dear respected! i've checked the external reference links, but i'm still unable to understand how to calculate values of R and C in the gyrator circuit, which'll make gyrator equivalent to my required values of inductances. Could you please put all those equations here?