# Question on measuring inductor coils

Discussion in 'General Electronics Chat' started by keithostertag, Mar 12, 2014.

1. ### keithostertag Thread Starter Member

Oct 4, 2012
48
2
I found this set of vintage Phywe inductors at a yard sale and thought they might be fun to play with.

They are marked 300 (4A), 600 (2A), 1200 (1A), and 12000 (0.05A).

I assume the "A" figures are current ratings, but I can't figure the other numbers.

All these are approx the same size and shape, 1.25" diameter coil form about 2.5" long.

Using this webpage to estimate the inductance:

http://www.dos4ever.com/inductor/inductor.html

And the values don't come close to the coil markings. Here are the figures I measure:

300 (4A) coil- 2.3mH (2300uH), DC resistance = 0.65 ohms
600 (2A) coil- 8.9mH (8891uH), DC resistance = 2.3 ohms
1200 (1A) coil- 30mH (30,000uH), DC resistance = 11.5 ohms
12000 (0.05A) can't measure, DC resistance = 1430 ohms

Working backwards using formulas, speculating the markings might refer to the number of windings, the figures I get don't correspond.

So what is your guess to what the markings are referring to? Am I simply using the wrong method of estimating?

I wonder if the square openings were designed to insert iron or other core materials?

Thanks,
Keith Ostertag

Jul 18, 2013
10,564
2,379
They were typically used in lab experiments and teaching as you already may have guessed, but there is usually a soft iron laminated bar that goes with them.
Max.

3. ### keithostertag Thread Starter Member

Oct 4, 2012
48
2
Hi Max- thanks. Yea, I assumed they were lab experiments and wondered about a required bar...

Do you guess an inserted iron bar would raise the inductance from, say, 2.3mH to 300mH in the case of the small one? Just trying to figure out what the markings refer to.

Thanks,
keith

Jul 18, 2013
10,564
2,379
They are about as old as I am, but they probably have more 'memory'
Max.

5. ### activex New Member

Mar 5, 2014
3
0
i think the other number is number of turns and the other is amp as you mention. this may look like a transformer, too, so, more turn means higher voltage but less current.

6. ### MrChips Moderator

Oct 2, 2009
12,449
3,364
They are used in physics labs for demonstrating the operation of transformers.

Pasco sells these:

keithostertag and #12 like this.
7. ### crutschow Expert

Mar 14, 2008
13,042
3,243
I also think the larger number is the number of turns. Thus when two are used as a transformer with a common core you can see how the relationship of the number of turns between the primary and secondary compares to the voltage ratio.

8. ### keithostertag Thread Starter Member

Oct 4, 2012
48
2
Thank you gentlemen! Very useful info, particularly the PASCO link.

Keith