This blog series is for the “Experimenting with Inductors” Design Challenge.  In this blog, I experiment with benchtop circuits and Autodesk Fusion 3D animation to explore the tennis ball model of electron flow to describe inductance in a circuit.  This content will be released in two blogs:  this introduction to inductors blog and my inductor application blog.  I hope you enjoy the finished project and, if not had already, gain a great understanding of inductors.  Thanks to the e14 team for sponsoring this awesome challenge!


See Also:  The Crazy Inductor Learn-o-Nator Put to Use:  Experimenting with Inductors Blog 2 of 2



Raising Awesome Crazy Inductor Learn-o-Nator



Thanks for taking a look at this blog.  I'm Sean Miller, a petroleum Mechanical and Reliability Engineering Team Leader.  By degree, I'm actually a Chemical Engineer who started as a Controls Systems Engineer with the chemical company DuPont.  After working just about every staff job in engineering, operations, and maintenance for 20 years, I was courted to petroleum refining where I have been the last 4 years.  Funny thing was, I didn't even know what an engineer was until my second year of college - I was a psychology major whose math teacher saw my computer skills (which were not so common in 1992) and gave me a scholarship to the big university on the condition I changed my major to engineering.  Today, my continued 37 year hobby of programming and tinkering often find there way to element14 where I continue to grow as a self made electrical engineer.


This blog introduces the contest package and theory behind inductors.  In the next blog, I’ll scratch build a multiple inductor circuit to handle all my power needs for Maker and industrial datalogging projects. 


To begin, let’s take a quick look at the inductor package that element14 and KEMET were so kind to provide.



The gang at element14 coordinated a design package1 for those accepted in the contest.  It's comprised of a Tenma LRC Meter, storage boxes, and a great assortment of KEMET inductors.


element14 Challenge BOM


Tenma LRC Meter (72-8115)

Most enthusiasts have a multi-meter that takes care of your voltage and resistance measurement needs.  The Tenma 72-815572-8155 finishes out your toolbox by providing measurement of transistors, diodes, capacitors, resistors, as well as providing a continuity buzzer.

Just take a look at these specs2:

Resistance (Ω) 200Ω/2kΩ/20kΩ/200kΩ/2MΩ/20MΩ ±(0.8%+1)

Capacitance (C) 2nF/20nF/200nF/2μF/20μF/200μF/600μF ±(1%+5)

Inductance (H) 2mH/20mH/200mH/2H/20H ±(2%+8)


This meter will serve us well as we experiment to build our power supply circuit project in Blog 2.


Duratool Storage Boxes (D00413)


Inductors (Multiple)

The KEMET inductor set came with both surface mount inductors and thru-hole.  Below is a picture in reference to a US Dime (18mm) under the microscope:

KEMET SMD (Left) and Thru-Hole (Right) Inductor Packages


Many have heard the water analogy for electrical circuits.  It compares water pressure to voltage and water flow to current.  Heck, water flow is even called “current”.  It’s that good of an analogy!


When learning about inductors and the concepts of electro-motive force and back electro-motive force, I find it easier to think about it at the electron level as physical balls – Tennis Balls, in fact.


“Why tennis balls,” you might ask?  For one, the tennis ball analogy is often used when introducing electron flow.  For me, tennis balls have a good contrast for animating when compared to ping pong balls and baseballs.  Meatballs just won't do.  So, without further ado, I introduce to you the Raising Awesome3 Crazy Inductor Learn-o-Nator:

Raising Awesome3 Crazy Inductor Learn-o-Nator


We’ll experiment on the test bench with our Learn-o-Nator concepts in the next section, but first let’s explore the tennis ball analogy.


Electrons-electrons are represented by tennis balls being displaced from the left side to exit to ground on the right.

Tennis Balls in a Tube are Analogous to Electrons in a Copper Wire



Inductor-our KEMET Inductor is represented by a paddle wheel driven by the tennis balls (electrons) as they flow to ground. The paddle turns a massive stone wheel that is hard to start turning due to its incredible massive size and weight. Likewise, it takes a bit to wind back down to rest once it has momentum.


Our Paddle Wheel Driven by Tennis Balls is Analogous to an Inductor



Piezo Buzzer-the piezo buzzer in the electronic world is also known as a beeper.  In this model, we are using a baseball card (Darth Vader collector card) to make a tick noise with each passing tennis ball (electron).  It’ just like the trick kids did with their bike spokes back in the day.  Since it takes a larger inductor than we are working with in this project, I'll substitute an LED in my circuits.


Analogous to a Piezo Buzzer, our noisemaker on the left is just like the cool noisemaker on the Right4




Resistor – the resistor of this circuit is where the tube necks down making it hard for the tennis balls to pass. 



Our Resistor is Just a Fitting that Reduces the Diameter of the Tube



It would take more force on the left of the Learn-o-Nator to get the same flow with the addition of that resistor.  Sound familiar?


V = I x R

or solving for I,

I = V / R


Ohm’s Law4



Studying the math, we see that the higher the resistance, the lower the current for a given voltage.


Now let’s study the Learn-o-Nator from the “ground up” (get it, “ground”?! )




In the tennis ball model of electricity, the flow of electrons is like tennis balls in a tube.  A battery is like a basket of balls feeding one side of the tube.  The potential from gravity will work a ball in the tube displacing a ball to ground on the other end.



Tennis Ball Pushed in One Side of the Tube Results in One Falling to Ground – Analogous to Electron Flow


Without any resistance and with a fast enough push by Superman, the friction from the balls sliding could melt the tube.  Likewise, in an electrical circuit, if there is no resistance to ground, the insulation would melt!

Insulation Melted on a Wire due to Lack of Resistance5



The next part to building the Raising Awesome3 Crazy Inductor Learn-o-Nator is to add a resistor.  Here it is shown as the reducer in the center of the image below.



A Tube Reducer is Like a Resistor in a Circuit



You can imagine that this added restriction would immediately make the balls harder to push through and, in turn, slow down the flow of balls to ground. This is just how a resistor would perform in an electrical circuit.




In this example, we have a 330 Ohm resistor.  Setting the meter to Volts, we see we have nominally 5 volts across the resistor.  On the right of the resistor (top right picture), we have 0 volts.  Also, to the left of the resistor (bottom right picture) we have 0 volts.  How can that be?! 


It’s because voltage is a delta - that is, a difference from a reference. In this case the reference is the black probe's location.  The meter reads very low milli volts, essentially zero, when the energy is the same at each probe. If you place the probe around the resistor you will find there is more energy on the left of the resistor than the right giving a difference of about 5V.



Let’s add in our noise maker in addition to the current limiting resistor in our Inductor Learn-o-Nator. Now when the balls start flowing, we hear the nostalgic tick of a baseball card flicking as the balls go by.


Our Noisemaker In the Tube

Now let’s see how that looks in an electrical circuit.  I substituted an LED in place of the buzzer so you can see it:


Probing Around an LED and Resistor in Series


You can see that there is a voltage drop across the LED and as well as the resistor.


Now, if I had that buzzer instead of the LED, as soon as a 5V hot is hooked on the left and Ground is connected after the resistor on the right, we have the most annoying sound every heard.




Dumb and Dumber6 Piezo Buzzer Impersonation


So, what if we were to put that noise maker of our Inductor Learn-o-Nator in a parallel branch in the circuit?  What would happen then?  Remember, voltage is a delta.  If there is no difference in energy between two points, there is no voltage, and there is no driver for electron flow.  Same with the physical world - if forces are equal, nothing happens.


Does this make Noise at the Baseball Card?  The noisemaker is in the center of the bottom loop.




Since, the forces are the same at the down tubes, they cancel out. In turn, there is no movement through the branch.  What about an electrical circuit?


Well, since there is no energy differential (voltage) across the buzzer, it has no energy to make a sound.  So, nothing happens except the resistor might feel warm as usual when voltage is applied.



Now it gets fun.  If it wasn’t magical enough that electrons flow without being seen, there is even a secondary invisible “force” to be reckoned with – EMF, Electro Motive Force. The word “force” is actually a misnomer – it’s actually considered “energy”, but back in the day when induction was first beginning to be understood and documented, it seemed like a force.  Just like the force felt from getting this big paddle wheel rolling in our Inductor Learn-o-Nator:



Our Paddle Wheel is tough to get turning

by pushing balls through the tube
But, it is easy once it is up to speed -

just like how Back EMF works with Inductors




To help learn about inductance, imagine pushing balls through our tube without the paddle wheel.  As we reviewed before, the balls would just take the path of least resistance to ground which is straight through the tube.  Forces at either down tube is the same on both sides even when you throw gravity into the mix.  In turn, since the same amount of force is opposing itself, no movement occurs in that lower loop branch.  One force would have to be greater than the other to make it head a direction.  In turn, we hear nothing from our noise maker because the balls aren't moving past it.




So, what happens when we add our inductor, the Paddle Wheel?  Well, like all objects, it will resist changes in inertia. That’s because, like good old Newton said, objects at rest tend to stay at rest – the first law of motion - inertia8.  It takes force applied over time to overcome the state of rest and build momentum. 


In turn, when we first begin to push on our ball with the paddle wheel installed, there is a motive force that pushes back.  This creates a resistance in the straight thru path that drives ball movement through the lower loop while the paddle continues to block the upper loop - until the wheel gains momentum.




With the force on the ball on the left continuing over time, the paddle wheel begins to build momentum and is easier to turn.  At a constant force, it hits is a flow rate with little back motive force.  When this occurs, the lower loop no longer sees a difference of forces at its main tube intersections, so no flow occurs in the loop while the wheel is at full speed.




When the wheel is first pushed, you can think of it as charging. If we blocked off the exit on the right, the wheels momentum would allow it to continue to spin until it winded all the way down.  In a frictionless environment, it would never stop.  But, in the real world, friction would cause resistance for continuing to spin and it would stop.  While winding down like this, the balls would go down the loop at the right tube branch back to the left of the paddle wheel until it the wheel came to rest!  It's expelling its charged energy even after the power source is removed.  Don't think of it, though, like a capacitor or water stored in a tank.  Think of it as inertial energy as a rolling ball.




This is pretty much how an inductor works.  Back EMF creates an opposing energy that chokes the current through the inductors branch.  As the inductor charges, the current gets faster through it until it is at steady state and full current is passing through.  In a nutshell, an inductor resists changes to current inertia.  Another way to look at it is that it always tries to keep its present current flow.  (I first thought current current flow ).  If it has no current, it will push back to hold it there, but always loses in the end.  If at full speed, say 100mA, and the power source is cut, its going to try to keep throwing electrons past it to maintain 100mA until resistance in the circuit slows it to zero.


This is why its important to have what's called a flyback diode in your inductor circuits such as motors and relay coils.  With out it, the inductor will through electrons to one side with no where to go until it "over pressures" the circuit (over voltage, that is) which usually means a component blows are it arcs across open switch contacts.  This is an expensive failure for transistors circuits.


Flyback Diode Circuit10




You'll notice, this is our Raising Awesome Crazy Inductor Learn-o-Nator Circuit!.  Well, almost, but rather than a noisemaker, it has a diode which limits flow to one direction.  It protects the circuit from the inductor building up mega voltage when the switch is open as it tries to keep the current flowing.


Let's look at an experiment where we use a KEMET 6.8mH inductor with an LED for the Flyback Diode.  We'll charge up the inductor with 5V and then pull the plug.  Will the LED be Lit?  Will it blink on startup?  Will it ever light?


Our Learn-o-Nator as a Circuit




In the above video, you'll see that the LED doesn't initially blink or light up.  It doesn't do so until the correct voltage drop comes across it to light it -AFTER THE POWER IS DISCONNECTED!!!!  Which is awesome.  This isn't capacitance - it's inductive energy acting like electron inertia keeping the current flowing past the inductor just as inertia will cause a boulder to chase Indiana Jones out a cave even up hill for a bit.


Here is the current flow shown at the three main stages of the circuit life: power on, steady state, power off:



Current Flow at Power Up

Inductor chokes the current due to its resistance to change

The current is ramping up to steady state flow

(green wires are just test rails for o-scope probes)





Current Flow at Steady State after Power On

Inductor is Passing Current

(green wires are just test rails for o-scope probes)





Power is Shut Off

Inductor is resistance to change, so it keeps tossing electronis passed it

using its EMF until resistance in the circuit "winds it down"

The LED gives a quick blink when it sees the voltage induced by the inductor

(green wires are just test rails for o-scope probes)




Other than tennis balls, here are some other examples of physical inductance due to inertia and dampeners that remind me of electrical inductance and emf:


Physical Inductor Examples
A water wheel in a river turning a shaft that drives a cog that turns a grinding wheel in a blacksmith shop.
A turnstyle door is pushed from rest.  It takes a bit of a push to get going versus spinning immediately.  This gives the user safe control of he door to prevent your hand getting pinched by the door and frame.
Under a Jeep Grand Cherokee, there is a steering damper (shock absorber).  Without it, the driver over steers horribly from left to right.
A Windmill in Holland keeps a steady speed driving a pump on a day of gusty winds


And, here are some electric coil applications:


Electronic Inductors Examples
Car Engine Starter - pushes the pinion gear forward to engage the engine flywheel to automatically crank the engine
Fluorescent Bulb Circuits - to limit current during its start and then raise the voltage immensely to light the ionized gas inside the tube.
Buck Step Down Power Supplies - with a diode, the inductor can ensure steady current while the switching regulator switches.
Current Transform - a coil that goes around a wire to allow one to infer current through the wire through a proportional current through the coil.
Stop Light Sensor - to detect vehicles at stop lights to let the stop signal system know who needs to go next at an intersection.



With all this new found knowledge, I'm ready to put it to good use.  My project will help my real world job as well as any home Maker project.  At work, from time-to-time, I dream up a data logging need in the field.  Here are a couple examples from my blogs in the past:

My Azure Sphere Coke Drum Health Monitoring System11

Note the regulator in the top left



My Coke Drum Growth Tracker12

Requires externally regulated power supply




MODBUS Remote Data Logger13

Requires externally regulated power


My dataloggers have a variety of designs.  One thing all my projects have in common is they all need some form of DC power, but the voltage and connectors all could be different.  The sensors and microcontrollers typically need 5V or 3.3V.  Depending on the situation, I may only have a certain voltage available.  For instance, in the field, I might be able to find 24V from the Distributed Control System (DCS).  Also, we have a lot of small 12V SLA batteries. For low power projects, a 9V will do nicely.  The power plugs could be 5mm barrel jacks, micro USB, or USB min-B.  The microcontrollers for my dreamed up dataloggers are typically Arduino Megas/Unos/MKRs, Raspberry Pis, or BeagleBones.  Another common thing to have is 5V/3.3V rail supply and I2C busses.


So, for Blog #2 of Experimenting with Inductors, my project will be to two circuits that can handle up to 3 Amps each to convert any supply 24V and under to 5V and 3.3V.  The KEMET Inductors will be the center of attention for taking all those different power sources to correct voltages.  I'll run some experiments under the O-scope as well.



Well, this blog was quite the ride!  I went from knowing nothing about inductors to dreaming about them every night.  Now everywhere I go, I see an example of inductance.  I hope you do, too!  The Raising Awesome Crazy Inductor Learn-o-Nator is just a virtual model, but I hope it helps others understand the magic that is behind emf as well as physical inertia.


One thing I also learned was what makes KEMET inductors perfect for my builds - particularly, their metal composite inductors.  Due to the coil being surrounded by a metal composite, the KEMET inductors can take high amps in an extremely tight package allowing my power supplies to have an unnoticeable footprint in my designs.

KEMET Metal Composite Inductor14


Look for my next blog where I apply these new skills along with KEMET's great set of inductors to design a board to power industrial data loggers and Maker embedded solutions.


See you soon,




  1. Experimenting with Conductors by Pauline Chan
  2. Tenma 72-8155 Datasheet from Farnell
  3. Sean and Connor's Raising Awesome Youtube Channel
  4. Ohm’s Law on Wikipedia
  5. What Boys Do by Ken Smith Photography
  6. Know Your Motorcycle Well
  7. Dumb and Dumber Movie Clip
  8. Newton's Laws of Motion on Wikipedia
  9. Skyrim on Wikipedia
  10. Flyback Diode Circuit Image from Wikipedia
  11. Makevember Project - How Much More Can a 140 Foot Vessel Grow?
  12. Avnet Azure Sphere Coke Drum Health Monitoring IoT AI
  13. Big Petro Maker Magic:  $100 Datalogger That Can Save Millions
  14. KEMET Website
  15. The Crazy Inductor Learn-o-Nator Put to Use:  Experimenting with Inductors Blog 2 of 2