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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.

?

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zanzarista
zanzarista

Reply 7 years ago

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
gmoon

Reply 12 years ago

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
Kiteman

Reply 12 years ago

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

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kelseymh
kelseymh

Reply 12 years ago

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
westfw

12 years ago

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
Kiteman

Reply 12 years ago

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
Big Bwana

Reply 12 years ago

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
Kiteman

Reply 12 years ago

Oh?

(Google)

Email away!

Thanks, BB

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Big Bwana
Big Bwana

Reply 12 years ago

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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Kiteman
Kiteman

Reply 12 years ago

PM.

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chooseausername
chooseausername

12 years ago

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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chooseausername
chooseausername

Reply 12 years ago

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

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Kiteman
Kiteman

Reply 12 years ago

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

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ll.13
ll.13

Reply 12 years ago

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

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Kiteman
Kiteman

Reply 12 years ago

Neither did most of this site's membership!

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Kiteman
Kiteman

Reply 12 years ago

Oh, thanks also!