Coil formula and how to measure inductance

[Claude]

Hi everybody,
I got this coil formula (see image) and I wonder if l=coil lenght in inches is not rather windings thickness instead.
Also if some of the guru's could answer how can I measure the inductance. I have only a multimeter.
Thanks,
Claude

[Reg]

Re: Coil formula and how to measure inductance

Hi Claude,

Below is a link to one of the best inductance calculators I have found. The nice thing about it is the fact it seems to be very accurate and it is really easy to use.

One other nice feature about this calculator is you can select between inches, centimeters or mm.

Now, once you plug in the numbers and hit the submit button, you will get two answers, the first is an approximate inductance and the second is a .1% accurate inducatnce.

Use the .1% inductance answer and you should come up with an answer that will be very close to what you will measure.

Now, calculator asks for three things, the diameter of the coil, the number of turns, and the length of the coil.

The length of the coil will be the thickness of the windings, which is typically about .25 of an inch, like you mentioned.

I just use .25 and come up with a calculated inductance that is normally within 10% of the actual measured inductance. Actually, the forumla is generally closer, maybe within 5% on the coils I make.

If we take your example and plug in the same knowns into the calculator on the website, 11" diam, and .25" for the thickness (length), the calculator comes out with 19 turns equalling 295.867... uh.

I am sorry, but I don't know of a way to measure the inductance just using a VOM, especially if it is a digital. Hopefully, someone else has an idea that will work.

I hope this link makes things easier.

Reg



Inductance Calculator

[William]

Re: Coil formula and how to measure inductance

Hi Claude, If you e-mail me I will sent you a pdf file with an adapter to measure inductance using a multimeter. William