So what is an Ignition Coil? An Ignition Coil by dictionary terms an induction coil that converts current from a battery into the high-voltage current required by spark plugs.  An Ignition coil is like and can be used as a high voltage transformer, and as a transformer, it contains two windings (primary and secondary) wrapped around a steel/iron core. The ignition coil uses a rod core, instead of the classic transformer design, though there are some transformer shaped ignition coils. The whole winding (primary and secondary) is immersed in a casing filled with oil. The primary coil has a low number of turns while the secondary coil has many turns which causes the HV output.

The ignition coil is one of the most important parts of a car as it  makes the high voltage output (around 10 - 20kV) required for the spark plugs. In older model cars, the initial 12V current is regularly interrupted by a contact breaker in the distributor while the engine is running. Now days, solid-state switching using IC chips is used as they are simpler and more efficient. So what makes an ignition coil work?

As previously stated, an ignition coil is like a transformer, and works by electromagnetic induction. When current is applied to the primary coil, a magnetic field is created. When this current is removed, the built up magnetic filed collapses and this induces a current on the higher wound secondary coil creating a HV spike. This happens extremely fast (many times a second ) creating an visually apparent continuous arc, which is passed from the HV output to ground. (see Diagram Below)
 

Now that we all have an understanding of how an ignition coil works..... An ignition coil makes an excellent beginner high voltage generator. They are also readily available and very hard to destroy. Ignition Coils come in two forms, cylindrical oil-filled types (see picture) or square ones.  As stated before, too work an ignition coil needs a pulsing current through the primary to create HV off the secondary coil. The setup on the right seems to be the simplest setup.

Besides the fact that this setup is extremely easy to make, its also quite cheap because there are only three main components.  Due to the fact that it runs off Mains 120V AC, it can be extremely dangerous. The capacitor (s) included can store a huge amount of electricity so always remember to discharge it (them) after use or to perform maintenance. On the right, you can see my final setup.  If run from a true car battery, the final HV output is a lot higher if run from a car battery, but running it off the mains is a lot more portable . There is some arcing over from the HV output to the ground. i I think the only solution would be to immerse the whole thin in oil, but doing that is sort of messy, so I'll have to build some better insulation. Below is a slap-together diagram of my setup:

Not many circuits get any simpler than this, although now your wondering...how does it work? T. The dimmer switch contains a "device" titled a triac. A triac is an electronic switch which triggers in sync with the mains frequency. The potentiometer on the light dimmer adjusts the timing of the triggering. As the triac triggers, it closes the circuit consisting of the coil primary, the capacitors and the AC mains. The following happens in order. The capacitors discharge into the ignition coil, then recharge again from the mains through the ignition coil, to the opposite polarity. Once the capacitor is charged, the current drops  to zero which makes the triac to turn off. During the brief period when the triac is off, the line voltage goes through zero and builds up in the opposite direction. When the light dimmer knob is set correctly to about fifty percent, the triac fires at the exact time the line reaches its peak voltage in the opposite direction, so the coil gets slammed with the full line voltage, plus the full voltage of the capacitor. The ignition coil gets hit with both voltages in series.  Then this whole process is repeated over and over (about 90-120 times a second).

Besides a soldering iron, some HV or high gauge insulated wire, you only need a few other items. Many junk auto supply places may give you an ignition coil for cheap or free (just tell them its for a science fare project).  Due to the age of the coil you might get, you may want to wash off the grease and grime.

A light dimmer is very easy to find - any local store that sells hardware should have one (I got mine at Wal-Mart). Try and find a rotary  dimmer, there are the more durable and the cheapest. The higher wattage the dimmer has the better rating, the better. (Mine is 600W) . Now for the capacitor... You will need an AC capacitor of anything from 0.1 microfarads to 20 uF.  30uf is about the limit for capacitor rating. I don't suggest you use a bigger one, and  at any voltage from about 250-600V. They all work, but the bigger the capacitor, the greater the output power. If the cap is too big, the ignition coil will overheat. My coil used two 250V 270uF wired in series which equals 500V 135uF.  I recommend you get a better capacitor because I can not run mine for very long without overheating .The last step is to connect the wires.

Due to the output of the Ignition Coil, insulation is key. There are a few ways to insulate against high voltages. In order to have enough insulation you must pay attention to clearance. Clearance is easy enough. You have to watch the distance between conductors on the coil. 1KV can arc 1.1mm (this is a good way to estimate voltage) .  Any arcs that are "arcing" between surface other than the intended gap it due to excess electricity.  The one way to stop this from happening is to increase the distance the arc has to travel, therefore expending more energy.  Remember that electricity will always want to take the easiest path to ground. Now on to the fun stuff.....

Here we have to arc examples. The one on the top seems to be one giant "thread" due to my shakiness.  In the second shot, which is more clear, you can see the multiple threads of the arc.  When ever there is high voltage devices, there are lots of Electro-Magnetic waves produced.  The most noticeable affect I experienced was quite noticeable static on the telephone.  1 KV and arc approximately 1.1mm.  There are 25mm in 1 inch.  So in the above shot that arc is about 25KV.  The largest arc I have made is about 30-40mm so that equals 30-40KV.  

I first build a poor mans plasma globe, or more like a plasma discharge device, using a 500V capacitor bank.  (See the first picture)  Sure its only instantaneous, but its still cool.  Now that I knew it worked I decided to hook it up to my ignition Coil.  If 500V its good what about 30,000!  It wont work the same as a real plasma globe because of the low frequency and the fact that it can kill you if you touch it.   There are arcs present inside and outside of the light bulb.  If you were present in the room you would notice that the arcs are a lot more purple that blue. Scroll Down For a Video!

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Here is a video of my plasma globe in all its glory!
(you need QuickTime player to view the videos which are .MOV format)

Ignition Coil Plasma Bulb: plasmabulb.mov (coming soon) (799kb)

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