Inductance calculator

Discussion in 'Electronics Resources' started by someonesdad, Dec 3, 2010.

  1. someonesdad

    Thread Starter Senior Member

    Jul 7, 2009
    I've written an Open Office (3.1.0) spreadsheet that is aimed at hobbyists who want to calculate the low frequency inductance of various common configurations of wire. You can get the spreadsheet and an explanatory document here. Since the file will likely evolve over time, I haven't uploaded it to AAC so that I only have to maintain it in one place.

    Remember, I'm an electrical hobbyist, so go easy on the EE bashing in case I've messed up technically. :p If you do find errors or places where things could be improved, please send me email and I'll fix the tools.

    Warning: messing with inductance calculations can be hazardous to your free time. You'll soon be knee-deep in elliptic functions, Kelvin functions, power series, etc. and saying to yourself, "Oh, just one more function..." I finally caught myself and realized all I wanted was something that would give me a 10% or so estimate of the inductance, as I'm not designing inductance standards. Thus, a spreadsheet with simple formulas is an entirely adequate tool.
  2. someonesdad

    Thread Starter Senior Member

    Jul 7, 2009
    I had a little time to play with the spreadsheet today and found a few problems. I've also added some new cases. The version on google code will be dated 4 Dec 2010.
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    I'd like to see your spreadsheet, but I'm not gonna install Open Office in order to see it.:(
  4. SgtWookie


    Jul 17, 2007
    If you have Microsoft Office installed, you can download updates that allow reading/writing of those file formats.
    I take it back; I can't read it using Excel 2003 and the converter.
    Last edited: Dec 5, 2010
  5. someonesdad

    Thread Starter Senior Member

    Jul 7, 2009
    Since I don't use MS Office, writing it in Open Office was my only choice. I perfectly understand not wanting to download a huge amount of stuff just to use one program.

    SgtWookie, I'd be interested in knowing whether these add-ons allow people to use the spreadsheet in Excel. It's likely some things won't come through. For example, I put the equations used next to every inductance calculation and OO's equation language feels similar to TeX/LaTeX, but MS Office had the most gawd-awful implementation for equations. I'd be surprised if MS wrote the code to convert things.

    More importantly, the BASIC macro environments of MS Office and Open Office are different (at least they were a decade ago). Since I haven't used MS Office in about a decade, I won't state absolutely that OO's macros will work in MS Office, but, again, I'd be quite surprised if they do.

    I fiddled a bit more with the spreadsheet today and just uploaded a third version. It now includes the ability to calculate the resistance of a chunk of wire at different temperatures. It performs the calculations for:

    1. Single layer air-core solenoid
    2. Multiple layer air-core solenoid
    3. Straight round wire
    4. Loop of round wire
    5. Rectangle of round wire
    6. Regular polygons (sides 3, 4, 5, 6, 8)
    7. General planar loop of round wire
    8. Planar spiral
    9. Two parallel wires
    10. Wire parallel to ground plane
    11. Parallel rectangular traces
    12. Wide trace over ground plane
    13. Coplanar traces
    14. Isosceles triangle loop of round wire
    15. Coaxial cable
    16. Toroidal inductor
    If you find errors or omissions, please let me know via the email in the documentation and I'll get things fixed.
  6. SgtWookie


    Jul 17, 2007
    I was mistaken; the add-in tool I downloaded wasn't from Microsoft; it was from SourceForge, and it only supports up to OpenDocument v1.1.

    MS Excel 2007 with SP2 and MS Excel 2010 could probably open the spreadsheet.

    I can read the text document with Word 2003 and the SourceForge add-in, but not with Excel 2003.
  7. tom66

    Senior Member

    May 9, 2009
    It doesn't work in Office 2010 on college computers; it opens, but no calculations can be made. It should work using OpenOffice on Ubuntu at home. Thanks for the useful tool.
  8. retched

    AAC Fanatic!

    Dec 5, 2009
    Great tool. Thanks.
  9. Duane P Wetick

    Senior Member

    Apr 23, 2009
    Inductance Calculations by Professor Frederick W. Grover, ISBN 0486495779 is THE definitive work on self and mutual inductance coils. You can find an affordable copy on

    Cheers, DPW [Everything has limitations...and I hate limitations.]
  10. someonesdad

    Thread Starter Senior Member

    Jul 7, 2009
    Grover's book is definitely something you should have if you're interested in making inductance calculations. By the way, you can buy a Dover reprint of the book from Amazon for $10. There's an errata here; also make sure to take a look around that website from David Knight, as there's lots of material on inductance calculations and some useful papers, such as Nakaoka's 1909 paper (a formulation still used today) and a useful compendium by Rosa and Grover from the mid 1940's; both are in PDF form.

    Grover was interesting -- he was born 3 years before Maxwell died and lived to be almost 100 years old.

    One of the problems with Grover's book, however, is it was written in 1946 before the times of cheap computation. Much of the book is focused on practical work that avoids lots of calculation; this is done by giving shortened formulas with table look-ups. It made eminent sense 60 years ago, but not today. In a few cases, people have derived empirical formulas for some of the tables; otherwise, one would need to go back to the original literature, which is not easy for someone without access to a big research library.
  11. SgtWookie


    Jul 17, 2007
    For those who don't have OpenOffice and don't want to install it on their computer...

    Have a look here:
    All you need is a USB flash "stick" memory and a PC that will access it. You can get a 4GB USB flash stick for around $10 nowadays.

    Make a directory on your USB stick called PortableApps.
    Download the Portable Apps suite to your memory stick, and run it to expand the suite.
    Choose just the Portable Apps Platform only, or the Suite Light (2mb and 50mb respectively)

    Then go here:
    Scroll down to Office, and download OpenOffice portable (~33mB)

    Install that to your USB stick. Drag and drop the OpenOfficePortable directory into the \PortableApps\PortableApps directory.

    To launch the apps menu, click on \PortableApps\StartPortableApps.exe
    This is a really cool tool, you can get some really handy applications, and it's all free.