Myth or fact? You can increase the force of your solenoid by removing turns (Part 2 of 3)

The solenoid: what's there to learn further about a passive component that is nearly 200 years old, dating back to the 1820s? After all, it's a simple passive component, isn’t it? And there is not that much to understand, right?

Well, yes and no. This article examines the common claim that the strength of a solenoid can be increased by removing some turns from the coil. In the process we look at formulations for inductance, power, energy, and force. The end result clarifies the roles of several solenoid parameters, and the effect of the number of turns may be surprising to many readers. Those who would prefer to skip the mathematical details can find a qualitative explanation in the conclusion.

We are presenting this article—which includes equations, models, and analysis—in three parts, as pdf files:

Part 1: Introduction; Equivalent Circuit; to read it, click here.

Part 2: From Energy to Force; Additional Discussion; to read it, click here.

[Editor's note: some readers have reported that Part 2 equations are not rendering properly in the pdf. If that's the case for you, please try this alternate version here, where Part 2 starts at the bottom of the first pdf page "From Energy to Force", and ends with the beginning of Part 3 (Conclusion).]

Part 3: Conclusion; References; and Appendix; will be available January 23, 2012.

About the author

Paul H. Schimpf holds the B.S., M.S., and Ph.D. degrees in Electrical Engineering from the University of Washington, with respective degree specialties in digital electronics, embedded signal processing, and modeling electromagnetic fields in complex domains such as the human body.

 He previously worked in the electronics industry for 13 years at Honeywell Marine Systems in Mukilteo Washington (which later became a division of Alliant Techsystems, Hughes Aerospace, and Raytheon), where he attained the level of Senior Principal Development Engineer, prior to entering a career in academics. He was previously a tenured Associate Professor of Electrical Engineering and Computer Science at Washington State University, and is presently Professor and Chair of Computer Science at Eastern Washington University.

One of his hobbies is the restoration and repair of arcade games, of which he presently owns three:  a Chicago Coin Twin Rifle (electro-mechanical), a Stern Meteor (early solid state), and a Williams Fish Tales (late solid state). Paul recently designed a printed circuit board to interface an Arduino Mega to 85 different Bally/Stern pinball machines so that his embedded systems students can program pinball game logic using a modern processor. The board includes the capability to play sound effects from WAV files stored on an SD card.