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How to Identify or Measure Inductance? Answered

I am gathering the parts for an ible, but I am short one part: a 12mH inductor.

I can spot some inductors in electronic garbage - the wire coiled around a ferrite loop - but there are also solid state inductors. Plus, the inductors are not usually labelled with their values.

How can I measure the inductance of an inductor with a volt-meter and an ammeter, but without access to a sine-wave generator?

Is there some simple trick that would get me "close enough" to the true value? What would be really useful (but probably doesn't exist) is a chart or formula where you plug in the size of the core and the number of turns around it and out pops the inductance value.

?

21 Replies

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gmoon (author)2008-06-29

I've bookmarked a couple links for this myself; though I have yet to try it.

http://engr.nmsu.edu/~etti/fall96/electronics/induct/induct.html

Owens bridge inductance meter

The second link looks like the business....but it's a bit much if you need to measure just one inductor.

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zanzarista (author)gmoon2013-02-18

I've used the fomula in the NMSU.edu website with sucess. The resultant values will vary a little based on the frequncy used, but that's the nature of inductors anyhow. I've also noticed that no one has mentioned using an LCR meter here. I found one on AMAZON for less than $30 dollars that measures inductors, capacitors and resistors (hence the LCRname) and does so with some accuracy. It's on my wish list at Amazon..

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gmoon (author)gmoon2008-06-29

Oh, and if you don't have a signal generator, use a small step-down transformer, 6V or something. The frequency of the mains is a little low, but should get you in the ballpark... (50hz for euro?)

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Kiteman (author)NachoMahma2008-06-29

I tried that, but I don't have a signal generator.

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Goodhart (author)Kiteman2008-10-22

I remember doing this in the past but have since lost the "configuration" I had (as well as the resistance decade box I made back then), just using a step down transformer and a VOM (plus the decade box of course)

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kelseymh (author)Kiteman2008-10-22

I see that you've gotten sufficient links from others to solve your immediate problem, but no one mentioned the underlying issue.

You can't measure inductance with DC: you need a varying current in order to invoke Lenz's law and measure the voltage drop: deltaV = -L dI/dt. You might be able to do it using your 50 Hz AC straight from the wall, assuming it's stable.

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westfw (author)2008-06-29

12mH is a pretty huge inductor, assuming that a "milli" m and not a mis-type "micro" u. Counting the turns/etc may not be useful because one of the factors in the equation is the magnetic permeability of the core material, and unless you have an air-core inductor, the core material is just as unknown as the inductance itself, and can vary over 100x even for different types of identical-looking ferrite.

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Kiteman (author)westfw2008-06-29

I checked the instructions, and it's 12mH, and the part number matches. I'm waiting for emails from companies that turn out to be all over Europe to see if they can get me one. It's a problem because the manufacturer is American, and the (environmental) rules changed recently? Anyhoo, we'll see. I'm reluctant to go into details because the project so far does not exist on the site in any form, and I'd kind of like to be the first.

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Big Bwana (author)Kiteman2008-06-29

Coilcraft offers several and they are RoHS compliant, and if you ask nice they will give you a free sample...

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Kiteman (author)Big Bwana2008-06-29

Oh?

(Google)

Email away!

Thanks, BB

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Big Bwana (author)Kiteman2008-06-29

Enjoy, And remember it's one to use, one to lose, and one to abuse so order three.... And what are you building ?

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chooseausername (author)2008-06-29

As far as I recall, if you can count the number of loop, measure the diameter of the wire, and the average diameter of a loop, you could calculate the inductance ... There are also some inductor that are packaged like resistors. A coulour code is used to identify their value ... Unfortunately, I can't help you more, because I forgot almost everything about inductors ..........

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user

(See wikipedia for the various formulae if you want to calculate it by yourself)

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Kiteman (author)chooseausername2008-06-29

Oh, thanks - why did I not think to check Wikipedia?

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ll.13 (author)Kiteman2008-06-29

Wikipedia didn't exist in the '80s, 90's

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Kiteman (author)ll.132008-06-29

Neither did most of this site's membership!

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Goodhart (author)2008-06-29

I have always had my share of trouble with this also, but I did find one detailed reference in the book "Foundations of Electronics: Circuits & Devices (link to excerpt on inductance here)"

I hope this helps in filling in any gaps Wikipedia might have left.

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