Ignition Coil Spark Generator

This is probably one of the easiest high voltage projects I have ever stumbled across. For the cost of an ignition coil and a trip to RadioShack, I was able to intermittently interfere with antenna reception in my household for years.

The cool thing about car ignition coils is that they are essentially miniature solid-state Tesla coils—just like their older cousin, they essentially convert a low voltage, high current power source (such as a 12V, 10 amp car battery) to a high voltage, low-amperage current (such as that irritating 1000V, .003 amp shock you get from a doorknob). Purists will stop me here: technically speaking, Tesla’s original patent called for an open-air circuit, with energy transfer through a “resonant coupling” between two coils with no electrical connection (like a radio antenna and receiver). But the legacy of the Tesla coil lies in the general idea of transformers (the electrical component, not the Hasbro automatons), which are vital to almost every modern electronic device.

Transformers (ie, increasing or decreasing voltage while doing the opposite to current) rely on one of Nikola Tesla’s most important inventions: alternating current. We’ve all heard the description of the electrons wiggling back and forth in the wire instead of flowing though, but that description obscures the true beauty of AC. A better way to visualize AC  is as waves in the lattice of metal atoms. When I took high school chemistry, transition metals were typically described as a “sea of delocalized electrons.” This epithet explains many meaningful properties of metals: they’re literally just a fixed atomic lattice containing a bunch of electrons that constantly float around, uncommitted to a single parent atom . This means that something like an incident electric field can very easily cause the electrons to move: in DC current, a constant electric field makes all the electrons move in one direction. While this carries kinetic energy very well, a common misconception is how it does so: electrons move incredibly slowly, and so the current is not due to a torrent of electrons suddenly cascading through the circuit. Rather, the observed current comes from a large number of electrons getting a tiny boost in velocity– their power is in their sheer numbers, rather than by their individual speeds. In fact, it actually takes about 4 hours for a given electron to make the round trip from your light switch to your ceiling fan– most of the power that travels in the circuit is due to large numbers of slow electrons arriving at the light bulb at the same time.

In alternating current, it’s not the particles themselves carrying the energy—it’s a disturbance in them. In fact, when you flip a light switch, an energetic electromagnetic field travels through the wires in your wall at the nearly the speed of light (because, after all, light is an electromagnetic field). It might slow down some due to other interactions with the metal in the wire (light also slows down when it travels through non-conducting materials, like distilled water), but for all practical purposes the change in current travels super fast. Tesla’s AC was brilliant because it exploited the fact that the particles don’t even have to move at all to carry a lot of energy. Going back to the sea metaphor, imagine how long it takes a single water molecule to travel from Russia to the US, even if currents are steadily eastward. Nonetheless, things like tsunamis can still do a lot of damage; not because of individual particles carrying energy over the entire ocean, but rather because every particle between Russia and the US jumps up and down a little bit to carry the wave. Likewise, when you hit an AC switch, you basically trigger a series of well-timed kicks of energy to the metal lattice (the wire), each of which sends a nice wave traveling through the sea of electrons. Because the light bulb converts the energy of the sloshing electrons into heat and light, you need to keep making waves (using power) in order to keep it going.

The cool thing about kicking the electrons is that the resulting current changes in time– and so it can cause other things to change in time as well. Within an ignition coil, a magnetic field is set up in a wide set of wire loops every time a kick passes through that part of the circuit. When the current stops (the wave passes), the magnetic field collapses. Tesla thought to put a second coil inside the first, so that this collapsing magnetic field has somewhere to go. Just as running current through a coil created a magnetic field, running a dying magnetic field through a different coil will create a current. But say that I’ve made my second coil out of 100 turns of wire, while my original coil only had 10. The voltage induced on my second coil will be 10x my original voltage, and my current will be 1/10 it’s original value. In ignition coils, this ratio is more like 1000:1, allowing me to take a modest input voltage and make a nice, long spark.

It’s important to note that the two coils have no electrical connection between them– the magnetic field literally reaches one coil from the other and transfers the energy (a concept that is the basis of radio communication). Thus ignition coils have four terminals: a primary coil where you can connect a battery, and a set of secondary terminals that are the high voltage outputs.

There’s just one caveat: the magnetic field has to begin to die in order to be resurrected on the second coil. This means that the current that created the field has to come on and off as well– a requirement perfectly suited for AC current. The trouble is that a car battery is DC, and so all it does is pour electrons, rather than make waves.

Your car solves this problem by turning the DC on and off really, really fast using a device known as a distributor, which causes the current to stop and start several times each time a wheel rotates. Each cycle makes a new kick of energy pass through the circuit and thus creates a new ignition spark in the engine each time (and thus creating a steady, continuous set of rapid combustions that allows the car to run smoothly). This used to be done mechanically, but recently integrated circuits have largely replaced physical distributors.

For my project, I faced a similar issue of creating adequate waves in my ignition coil. If I attached the coil to a 12V lantern battery and then rapidly connected and disconnected my leads, I would get sparks, but only as often as I was able to manually connect and disconnect the switch. I considered using modern integrated circuits to do the switching for me, as occurred with distributors in cars, but I realized at the time that I barely knew how to send an email, let alone program an integrated circuit.

A trick I found online is to use what’s known as an electromagnetic buzzer, or a circuit that keeps trying to disconnect itself. Common devices known as N.C. relays have four terminals: two for control, two for output. The control terminals are electrically connected, as are the output (although the latter have a special magnetic switch connecting them). If I connect DC power through the two control terminals, it activates an electromagnet that then pulls open the output switch. If I disconnect power, the field goes away, and so the output terminals close up again. Thus in an ambient state, the N.C. relay is Normally Closed—anything connected to the output terminals will have a continuous circuit through the terminals.

A good way to consider this is that the N.C. relay is a logical NOT gate: if I have power through the inputs, then power is not allowed to run through the outputs. If the inputs lack power, then it is possible for power (in a separate circuit) to run through the output terminals.

N.C. Relay

An N.C. relay blocks current through another circuit when power is run through one of its switches, but allows the other circuit to flow when no power is being run through the input terminals. This illustrates how one circuit can control another, unconnected circuit.

The electromagnetic buzzer uses an NC relay to set up a paradox: what if a circuit were to run into one input terminal, out the other, back in one output terminal, and then out the other and into a circuit? Running power through this configuration would definitely provoke the electromagnet, which would then open the switch- and thus break the circuit. Since the magnet then turns off, the switch closes again—causing the magnet to turn back on, the the cycle to repeat. This means that, if I wire a common relay up correctly, I can end up with an electromagnetic paradox, a circuit that constantly strives to turn itself off.

The two states of an EM buzzer. The circuit constantly oscillates between these positions.

This is the basis of the electromagnetic buzzer, which gets its name from “buzzing” between on and off. If I were to plot the shape of the current in the circuit over time, I would get square waves, where the current runs for a short period at a constant DC value (making a straight line on the plot at this value), and then stops for another regular short period (making another straight line at zero).

Returning to the ignition coil, this means that all I need to put AC through my coil is my battery, the N.C. relay (correctly wired as a buzzer), and my coil. You can see in the video that this process creates a constant spark at a fairly low frequency (you can see it jumping, for example). In true Tesla coils, the sparks jump so fast that they give the illusion of being animated or continuous (at which point they are called “streamers” because they appear to stream out of the terminal).

The full circuit for the continuous ignition coil driver. This should produce 2-3 inch sparks at a steady rate.

For an even higher output voltage (3-5 inch sparks), another coil can be connected in reverse parallel with the original coil primary terminals (ie, in parallel with wires crossed). Sparks will jump between the output terminals of the two coils because they will have opposite polarities due to the reversal.



Incandescence from a pencil lead

Here is an old video of a basic incandescent light source made from a pencil lead and DC voltage source:

I liked this project because it reminds me of Edison’s original lightbulb design, which also had a carbon filament (made from charred bamboo). Naturally, the carbon gets exceptionally hot (incandescence, by definition, is the process of heating up an object enough that it releases light), and so this method risks shattering the carbon rod in a process similar to what happened in my arc welding project.

Most modern incandescent lights house a tungsten filament within a vacuum glass envelope, which extends the lamp lifetime by preventing the filament from oxidizing (“burning out”) in the air. Many theatres use what are known as Tungsten-Halogen bulbs, in which a reactive gas is contained within the envelope. As the filament burns, it reacts with the gas in an extended process that ends up eventually returning elemental tungsten to the filament. Of course, not all of the tungsten is deposited on the filament, causing TH lamps to gradually develop a “mirror” coating of tungsten that impedes their luminosity. But while this process is far more efficient than Edison’s original vision for incandescence, the mechanics of the process remain essentially the same.

Physically, incandescence can be modelled by what is known as a “blackbody” radiator, a hypothetical object that reflects no light. If such an item is heated to a specific temperature, it will start to release light of a very specific, predictable color (known as its “color temperature”). While no objects are truly black bodies, the construction provides a useful guide for predicting the behavior of real-word systems. As the name implies, by examining the color temperature or object, scientists can infer the temperature—a process vital to the study of distant stars and galaxies.

The reason for the relationship between color and heat is simple: As bodies (black or otherwise) absorb more and more heat, their electrons begin to jump to higher energy levels, in a process similar to carrying a heavy ball up a set of stairs: If I am willing to put in a little work, I can move a weight up one step at a time. If I put in a little less effort than what is need to go up a full step, I’ll end up not moving the ball anywhere all; the ball can’t go up half a step. Likewise, only certain, discrete amounts of heat energy(known as quanta) are absorbed by the atoms within an object. As these are absorbed, the electrons move into progressively higher-energy orbits– higher steps. Eventually, something happens to knock them off their high horse, and they end up falling back down to their original orbits– just as eventually my cat nuzzles my ball and causes it to fall back down the stairs. In falling, the ball gets rid of all of its energy by clattering and damaging my tile floors; in the atom, the electrons release their excess energy by emitting light.

The color of light is closely related to how much energy it has, and so higher energy/temperature objects tend to release higher energy colors. Visually, this actually corresponds to cooler tones– red hot is less serious than, say, white-hot or blue hot. Thus when astronomers see a blue star, they can tell that it’s still young and hot, because its temperature and appearance are inextricably linked.

Of course, there are other ways to excite electrons and create light– fluorescent and LED lights make use of stimulation from electrical fields to move electrons up the stairs, often at far greater energy efficiency than incandescent lights. But many lighting designers still prefer incandescence, purely for the warm glow caused by its low color temperature.

Worth noting in the video is that the light tends to flash on and off at a steady rate. Instead of using a battery, I opted for a 60 Watt AC to DC converter. My model, which was bought from a portable refrigerator company, includes a special protective circuit that shuts off the device when the current gets too high. After waiting some time, the current resumes, only to find that the short is still present.

Arc Welding with 9V Batteries

I used to work intermittently as a theatre technician, doing a mix of carpentry and electrical work in order to build sets and lighting systems.

Once, for a production of “West Side Story,” our crew rented an old Hobart arc welder in order to build portions of the set using chain link fencing (subtlety was not included in the production budget). We were fascinated to discover that the welder is literally just an extremely powerful soldering iron, using a high-amperage DC current to simultaneously melt steel and forcefully eject molten debris.

I became interested in seeing whether the same effect could be accomplished on a much smaller scale using a lower-power DC source. In a stroke of good luck, I discovered that another theatre at which I was working was disposing large numbers of half-spent 9V batteries from its wireless microphones. These batteries are generally changed very often, since no theatre wants to risk Maria’s mic cutting out halfway through “I Feel Pretty.”

Since many of the used batteries still had plenty of energy, I started stockpiling them. A convenient feature of 9V batteries is the metal “claspers” that allow them to be easily connected together, which allowed me to connect all of my connected batteries in series to build a power bank of ~100 V DC.

Batteries are rated in ampere-hours, which is a unit related to energy content. The idea is that, if I have a 10 ampere-hour battery, I can draw one amp for ten hours, or 10 amps for one hour, or 2 amps for 5 hours, and so on. The only limit to the amount of current that can be drawn is the battery’s internal resistance, which will steadily heat up as the current increases.

In the video below, it is apparent what happens when my 81V C circuit of ridiculous amperage is discharged through a graphite rod (a pencil lead) onto a thin piece of steel wire. As the steel wire heats up, it gradually begins to melt, resulting in the orange glow you see at the end of the video. The strange cylinder I’m holding was the closest thing I could find at the time to a UV filter, since staring directly into the arc is inadvisable. Pardon some of the poor directorial decisions involved in making the video, but definitely watch the last ten seconds or so:

I’m guessing that the shattering at the very end is the result of the interior of the graphite heating up relative to the exterior, resulting in differential thermal expansion across the lead and eventual mechanical failure (this is also why your windshield shatters if you pour boiling water onto it in the winter). Fortunately, I was wearing goggles and gloves at the time.

I eventually had to discontinue my experiments, as the now-overheated batteries began to hiss at me. But what I like about this project is that it shows directly the connection between the low-energy electrical devices we encounter every day and the dramatic electric arcs that we encounter in science classrooms.