Introduction: High Voltage Car Ignition Coil Project

Picture of High Voltage Car Ignition Coil Project
Do you need a high voltage source for other experiments? What follows is a simple way to get 30,000 volts or more without soldering or fiddling with components. All you need is a automobile ignition coil, a household dimmer switch, a suitable capacitor, wire, a few common hardware store items, and you will have a high voltage source ready to go.

Step 1: Parts You Will Need

Picture of Parts You Will Need

First of course you will need an ignition coil. These are easy to find new or used. The common metal can type can be had new from J. C. Whitney for $18 and up, or you can buy them used from a local salvage yard. I got mine off eBay for about $9. They are Accel "Super Coils," capable of up to 50,000 volts. I recommend you get high value coils, if only for the better quality and higher safety factor.

Next you will need a household dimmer switch. Get the simplest, cheapest one you can find. Mine cost about $8 from Home Depot. It is rated for 600 watts. Get a cheap nylon cover plate to match it.

You will need a film capacitor. More about this critical component later.

You will need some appliance cords. I salvaged some from a toaster oven and a box fan. Leave the wall plug on one cord, as this device runs off household 110 volt AC current.

You will need a box of some kind to mount your components in. I had a wooden craft box lying around (bought at Michaels craft store for less than $5). It measures 8.5" by 5.5" by 3.25" and has a hinged lid. This proved to be a convenient size. You can get a electronics hobby box from Radio Shack if you like, but the wooden boxes are cheaper.

Other bits and pieces you will need:
(1) half inch PVC pipe end cap
about five inches of smooth metal rod, 5mm or 3/16 inches in diameter. Copper or brass is best.
(1) 10-32 size brass thumb nut
(1) 10-32 threaded aluminum standoff, one inch long
(1) 10-32 threaded rod, about 3 inches long
(2) brass cotter pins, 2.5" long
(2) alligator clips, preferably insulated. Mine in the photos aren't, so I had to sheath them in vinyl tubing.
(2) crimp-on ring connectors, sized to fit the cords you are using
(2) crimp butt connectors, ditto
a length of half-inch square basswood (four inches will do)
a spring clothespin
a wood screw that will fit through the pin's center spring
a couple of sturdy rubber bands
(2) small nylon zip ties
electrical tape, a crimp tool, wire stripper, etc.

Step 2: The Switch Box

Picture of The Switch Box

Stain your wooden box if you like, and give it two or three coats of polyurethane to seal it.

Measure the underside of your dimmer switch and mark out a rectangle on the lid of the box. Bore holes at the corners of the rectangle, then with a keyhole saw or X-Acto saw cut out the rest of the rectangle. Mount the switch in the lid with two short wood screws. Install the trim plate over the outside of the switch.

With the lid open, take the length of half inch square basswood and glue it across the lower right corner. Allow glue to dry. Take the clothespin and place it on its side about halfway along the basswood brace. Screw an inch long wood screw through the center "eye" of the hinge spring. Don't tighten too much. Let the clothespin pivot a little.

Bore a hole low but centered on one end of the box. Feed in the electrical cord you have with the wall plug attached. Divide the cord about four inches or so (that is, using a sharp knife divide the molded plastic cord into two strands). If the cord is marked, or if you can trace the positive wire, attach it to one of the dimmer switch wires with a crimp-on butt connector. The other wire is the negative line.

Take about eighteen inches of two strand appliance cord. Remove any plug and strip all four ends. Split one end of the cord about eight inches. Bore two holes of appropriate size in the opposite end of the box and feed in the two strands separately, one in each hole. Connect the lower wire--the one by the wall of the box nearest you--to the power cord ground line using a crimp-on butt connector.

Split the other end of the output leads about three inches and crimp on two ring connectors sized to fit the coil's 10-32 terminals.

Attach an alligator clip to the as yet unused wire coming from the dimmer. Attach the other alligator clip to the other output wire. Put a nylon zip tie on the output leads inside the box, and a similar tie on the wires outside, to relieve any pulling stress on the wire. Cut a thick rubber band in two. Tie this several times around the power cord where it enters the box, also to relieve stress on the cord.

Step 3: Prepare the Coil

Picture of Prepare the Coil

Wrap a few turns of electrical tape around the output post of the coil. This will insure a snug friction fit for the PVC cap.

Bore a 3/16ths hole in the center of the PVC cap. This should allow your 3/16 rod to slide in, but be close-fitting.

Insert the brass rod in the PVC cap and press the cap over the coil's high voltage center post. Make sure the brass rod is in good contact with the bottom contact.

Screw the threaded rod into the aluminum spacer. Fit a brass cotter pin to the top of the brass rod and the threaded rod.

Slip the positive output lead over the positive (+) marked terminal on the coil. Use a brass thumbnut to secure it.

Put the negative output lead on the (-) marked terminal. Screw the aluminum spacer--threaded rod assembly over it and snug it down.

Step 4: The Capacitor--updated

Picture of The Capacitor--updated

This is the most finicky step in the project. Your choice of capacitor will determine how well (if at all) your coil works.

Use a film capacitor rated for at least 100 volts and 1uF. 100v may seem low, but the cap I used with greatest success is rated at 100v, while higher voltage rated caps only made the coil buzz.

DO NOT USE ELECTROLYTIC CAPACITORS! These are the ones that look like little metal cans. Even high voltage, high capacitance types failed on me *every* time. They got very hot, they bulged, and one even exploded. No joke--leave them alone! Stick with film types. There may be others that will work as well, but my best result came with a cap salvaged from a computer monitor circuit board.

It is marked:

I measured the capacitance of this cap with a multimeter and got a reading of 2.178 microfarads. With this cap I get good long sparks, cool operation, and no overheating of the coil, the switch, or the cap, although I have not run the coil for long periods. The longest I have let it run was for 60 seconds.

I mount the cap in the jaws of the clothespin. The lower lead goes to the output cord alligator clip, and the upper lead to the dimmer switch.

Update as of 3/23/09: I obtained some metalized polyester capacitors rated at 2.2 uF at 250V from an eBay seller . They work very well, and give a greater range of output on the dimmer (by this I mean I get more sparks at higher settings than I did with the 100v cap). The new caps are marked:


Tolerance is rated at 10%.

Update as of 4/22/09 While tearing down a surplus microwave oven, I came across an array of capacitors I thought I would try in the coil driver. (These are not the usual metal can capacitors associated with microwaves; they are high voltage film-type caps). A couple of 3KV caps did not work, but a 4.5 uF, 250 volt cap gives much greater sparks than anything I have used before. Discharges are longer, thicker, and louder. They are no longer blue-white, as with the previous caps, but a kind of vivid orange. Does this indicate a lower temperature, I wonder?

The cap is marked:


Update as of 4/18/10:
Even better results have been obtained using a 10 uF, 330 volt VIOT motor start-run capacitor. This is a large, oval metal-bodied cap I found on eBay. With the motor start capacitor the coil produces much more powerful arcs. I have used this coil and cap combination to power my Tabletop Tesla Coil with success. If you can get a motor start cap like this, by all means use it.

Step 5: Firing It Up--and What You Can Do With It

Picture of Firing It Up--and What You Can Do With It

So you have the parts assembled, and the coil ready to go. First make sure the dimmer switch is set at "off." On my slider model, there is a bump, or detente, at the lower end of the slider's travel to indicate the off position. Twist dial models often have a push-on, push-off power switch.

With the switch off, plug the power cord into a wall socket. I chose a cord that happens to have a RF (radio frequency) choke built into it. This helps damp any high power surges back up the wires into the house circuit. If your cord doesn't have one, you can buy clamp-on chokes at Radio Shack. These attach over your existing cord.

The dimmer switch has surge protection built into it. I understand this is normal for all modern dimmer switches. Read the packaging in the store before you buy. Some dimmers are rated for 600 watts, other for 750, etc. 600 seems to be adequate in my setup, even with the Accel Super Coil.

I also take the precaution of plugging into a GFI (Ground Fault Interrupt) wall socket. If there is a short, the breaker will trip.

OK, you are plugged in. Keeping a healthy distance from the electrodes, bump the dimmer switch on. I get the brightest, loudest sparks at the lowest setting of the switch. Pushing the slider up attenuates the spark until it eventually disappears, leaving only a strong humming. The coil is still active at this level, it's just not producing enough power to jump the air gap between the electrodes.

The gap affects the appearance and noise of the spark too. A close gap--say, an inch--gets you a loud, continuous blue-white spark. Opening the gap (CURRENT OFF, PLEASE!) thins the spark.

ALWAYS TURN OFF THE DIMMER AND UNPLUG THE POWER CORD BEFORE MAKING ANY ADJUSTMENTS TO THE COIL! This thing puts out, at my best guess, around 30,000 volts. It runs off household AC. This is a deadly combination, so don't screw around with it, OK?

THE CAPACITOR RETAINS A STRONG CHARGE EVEN AFTER THE DEVICE IS SWITCHED OFF AND UNPLUGGED. You can add components to prevent this, but my goal was simplicity. You can safely discharge the capacitor by touching both leads at the same time with the shaft of a WELL INSULATED screwdriver. Holding the tool by the insulated handle, short-circuit the leads. You'll see a flash and maybe hear a slight pop. Once the cap is discharged you can remove it, swap it for another, etc.

What can you do with the coil?

Sparks are fascinating, but there's more to be done. I have used the coil to power a "lightning ball," consisting of a clear incandescent bulb mounted on a porcelain base. If you attach one lead to the screw terminal base and the other to an outside terminal made from a bend of heavy wire (like a length of coat hangar) you can make a plasma ball. Unlike the cute plasma spheres you can touch, do not touch this one!

Someone's bound to ask if you can power a Tesla coil with this outfit. You will need other components to do so, but I would say yes. I haven't tried it, but I have read about others using ignition coils as power supplies for Tesla coils.

A search of the net can turn up other uses for a high voltage power source.

BE SAFE, PLEASE. Use good sense and good technique when handling high voltage equipment.

Update 12/10/2013: Here's another use for the spark coil-dimmer switch apparatus:

Step 6: Addendum: a Simpler, More Compact Version of the Coil Driver

Picture of Addendum: a Simpler, More Compact Version of the Coil Driver

After finishing this write-up, I wanted to try a rotary-style dimmer and see how it compared to the slider model I used first. Rather than go through the whole rigamarole of the wooden box, clothespin, etc., I just got a plastic electrical box (the kind contractors use when installing house wiring). Home centers and Wal-Mart have these very cheaply. I paid less than 30 cents for a gray plastic one. I next found a new rotary style 600 watt dimmer at Lowe's for less than $5. The dimmer, like any other household electrical switch, is made to fit a standard sized box like this, so it all went together very easily. With simple crimp connectors I wired up the dimmer to a 250v, 2.2uF film capacitor (25 cents for the cap) and used two salvaged power cords going in and out. Total cost, less than $6.

And it works just fine. The rotary switch is pushed in to be "on," then adjusted by twisting the dial. It seems to have a greater range of operation than the sliding switch.


Electrode55 (author)2017-06-24

Have you used anything to regulate the output and/or how have you connected into it?

Mr. Apol made it! (author)2016-10-11

Here's a diagram.

Mr. Apol (author)2016-10-11

The circuit is simple:

TshewangT (author)2016-10-09

Hey Paul,

I really like this project of yours and would love to try it out....but i am worried about my safety since we are talking about kilovolts here so i dont want it mess up while making any necessary connnections...i tried looking up the link you have given below ( but its broken or the page shows some wierd can you please mail me the ckt diagram to (

Thanks a lot!!!...

Deathstick (author)2016-05-22

Love it when people update things, LOVE IT! My favorite internet thing, UPDATES! You found other neat things and kept the dream alive! KUDOS!!

My least favorite trait of the internet is the "drop-offs". You've seen em. They have questions, you want answers. You search the net because you have a problem / idea / wanna try / need help...etc, you find 10-20 like individuals. After reading 5-30 pages on each forum, the thread inevitably goes dead, usually right before the elusive answer. Now you have 400 POSSIBLE answers/resolutions, thanks to the helpful diehard forum members and are now worse off than when you started somehow. You have found the "drop-offs". They get theirs, then drop-off the face of the Earth.

How to spot one:

'I'm gonna try "x" and "y", I'll get back.'******

Instructables is not a drop-offs free zone either. They post.... missing pics, paragraphs, a part, a list, then never respond to comments.

I digress.

Mr. Apol (author)Deathstick2016-05-22

Thanks. As long as the questions are rational, I always reply, and if I have new info to add, I do that too.


StanleyM16 (author)2016-01-09

awesome biefield brown apparatus. very awesome

Mr. Apol (author)StanleyM162016-01-13

Thanks! Have you built one yourself? I always like to compare notes.


cgosh (author)2013-09-30

It's customary to include a schematic (wiring) diagram that shows the electrical connections in a very clear form. One easy way is to just draw on paper, then cellphone-photograph it and post it. Another is to use Windows Paint program (mspaint.exe).

Very good instructable. The high voltage will give you a poke if you're careless, and can make flammable materials burn, but shouldn't be enough to cause any real harm, in my opinion (unless it makes you jerk your hand away and jam your elbow into your buddy's face -- or a wall). The 120-volt side is lethal.

crazy-blender (author)cgosh2014-09-26

It's accually lethal because unlike most transformers ignition coils are autotransformers which makes the secondary connected to mains making it lethal.

If you want it to be a little safer use an isolation transformer before the dimmer.

masonmilby (author)2012-09-27

could i use a 12v battery to power it also can i use another coil and a
GE 72F6211 CAPACITOR 10 uF 330 V thanks!

Mr. Apol (author)masonmilby2012-09-28

If you use a 12 v battery, you have to have some method of pulsing the current to the coil. In the old days cars used "points" in a distributor, a set of mechanical contacts opened and closed by a cam. In order to power a coil, you'll need a relay or some kind of circuitry (like a 555 timer) to pulse the input. You can't just hook up the ignition coil to a battery; it won't work.

10 uF at 330 V will work well unless the capacitor is an electrolytic type (in that case the cap may overheat and explode). Is this a film capacitor?


masonmilby (author)Mr. Apol2012-09-28

Is this a good capacitor also ill use ac 120v

Mr. Apol (author)masonmilby2012-09-28

Looks like a motor-run capacitor. It should work fine. 10 uF will give you a very hot, loud spark, which might melt your electrodes if you run it very long. 3 to 5 uF is cooler.

Beware of any capacitor! This simple circuit does not discharge the capacitor after you shut off the juice. It will hold a nasty, dangerous charge, so don't fool around with the capacitor even with the power off and unplugged!


masonmilby (author)Mr. Apol2012-09-28

How long do you mean?

Mr. Apol (author)masonmilby2012-09-28

Basically the charge can last for days or weeks. You can short it out with an insulated screwdriver, but for goodness sake be careful.


houdini0118 (author)Mr. Apol2013-02-08

what exactly do you expect to happen when its shorted with a INSULATED screwdriver?

Mr. Apol (author)houdini01182013-02-08

You discharge the cap without shocking yourself.


houdini0118 (author)Mr. Apol2013-02-08

insulated screw drivers are insulated right up to just before the tip or including the tip to prevent the screw driver from shorting things out when working on live electrical systems.

Mr. Apol (author)houdini01182013-02-09

That's one version, I guess. I simply mean a screwdriver with a metal shaft but has a handle that insulates the holder against the charge in the capacitor.


masonmilby (author)masonmilby2012-09-28

And would this one work?

Mr. Apol (author)masonmilby2012-09-28

That would be just about ideal.


masonmilby (author)Mr. Apol2012-09-28

will any ignition coil work

Mr. Apol (author)masonmilby2012-09-29

Short answer, no. The modern HEI and electronicly driven coils are not a good choice for this system. Try to find one of the old fashioned "can" coils, or an epoxy encased coil like the one shown in the project.


masonmilby (author)Mr. Apol2012-10-09

How do I measure the output voltage of an ignition coil

Mr. Apol (author)masonmilby2012-10-09

Lacking an expensive high voltage meter (which I don't have) you have to estimate voltage based on spark length:



masonmilby (author)Mr. Apol2012-10-29

I got a 1 3/8 inch spark length how many volts do you think is coming out of it?

Mr. Apol (author)masonmilby2012-10-30

An inch of spark is ~20 KV, so 1.375 inches would be around 28 KV or so. Just as a rough estimate.


sevise (author)2012-11-05

Hi,what use with smallmotorcycle to ignition plug(parallel conection)),
I used cap. 30KV 1000pf, to ignition coil's car it work good,but not small motorcycle'scoil
you can email me;

Mr. Apol (author)sevise2012-11-05

1000 pF (which the same as 1 nF) isn't enough, nor do you need a 30KV rating. What you should use is a capacitor in the low microfarad range (1 to 3 uF) with a voltage rating of around 400.


sevise (author)Mr. Apol2012-11-05

Hi,Paul thanks for your kind email,I will try 3 uf and 400volt as you suggess(this is pararail connecting,not series),please tell me how much voltage of secondry of small motorcycle ignitiom coil(about 125 cc yamaha),for car's coil is about 30.000 volt

Mr. Apol (author)sevise2012-11-05

No, the capacitor is wired in series. See the article and diagram here:

It's hard to say what the output of your motorcycle coil will be. It depends on the input voltage and the ratio of turns inside the coil, etc. I would guess it to be around 15,000 to 20,000 volts, but that's just a guess.


bswt (author)2011-08-15

how did you wire the film capacitor to ac power did you put it across the mains ?

Mr. Apol (author)bswt2011-08-17

See the article and diagram here:

Paul (author)2011-06-04

I built this, and I finally have a working hv source. I am worried about my safety though, because even at the lowest level on my switch with about a total of 10 seconds runtime and that wasn't continuous, it is very hot. I didn't use a capacitor and it worked fine, although it isn't powerful enough for a jacob's ladder.

Mr. Apol (author)jj.inc2011-06-04

You need a capacitor to buffer the coil and cut down on that overheating.

Paul (author)Mr. Apol2011-06-04

buffer? To me it doesn't look like it does anything at all

Mr. Apol (author)jj.inc2011-06-04

I have run my ignition coil (with capacitor) for minutes and it never gets hot.

Paul (author)Mr. Apol2011-06-04

ok, so it is on the 120v end right?

Mr. Apol (author)jj.inc2011-06-05

See the diagram here:

Paul (author)Mr. Apol2011-06-05

Now it isn't working, I tried going through the capacitor both directions to no avail, it is 100v and a 2.2 joules. Any ideas, I am going to try some more really fast, but this is the best capacitor for the job it seems.
Does there need to be a way to bypass the capacitor, I didn't pick up on it if there is. So maybe like a wire going from the dimmer to the + on the coil and a wire going through the cap to the +

Mr. Apol (author)jj.inc2011-06-05

100 volts is not enough. Try to get 200+ volts. I assume you mean 2.2 microfarads, not joules (joules don't figure in this).

Always use an appropriate capacitor or you face overheating, shorting, and failure.

PBT (author)Mr. Apol2011-06-06

Well you said in the instructable that you used a 100 volt one and you had to measure the capacitance because all it gave you was joules. I had almost the exact same capacitor and it didn't work.

Mr. Apol (author)jj.inc2011-06-06

Commercial capacitors are rated not only for maximum voltage and capacitance, but also for the tolerance of their internal components. These ranges are coded into the numbers and letter you see on the cap. If you have a cap rated at 100 volts, but the tolerance is plus or minus 20%, then obviously the cap is good at 110 to 120 volts without overstressing. Other 100 volt caps might only have 5% or 10% tolerance, and therefore will not be as resilient. My original film cap that was rated at 100 volts worked, but not as well as the motor run cap I use now, which is rated at 250 volts.

I can't answer every question you have because I don't what equipment you are using or for what purpose. If you use salvaged or 2nd hand parts, they may have weaknesses that cause them to fail more quickly than new components. (author)Mr. Apol2011-06-06

Are you using a DC or AC capacitor because, I have tried both and none work except for the electrolytic type which are DC for sure. I think that may be why they don't work, because they aren't rated for the AC, which would explain problems at voltages well below the top of their threshold. (author)Mr. Apol2011-06-05

He, he, I got it to work, it was really cool. I decided to give it a go with a can-type capacitor. It was 400v don't remember how many joules. Gave some really cool sparks for about 5 seconds. I was glad I finally had it working so I pulled apart my two rods and it would spark once and then stop, we would shut it off and then on and it would spark again, the third time it went tsssss..... and now I have to pull all the smoke alarm batteries. :( so how do I get it to work now, do I need bigger film caps.

Mr. Apol (author)jj.inc2011-06-05

Don't use electrolytic (metal can) type caps! They will overheat, explode, and even catch fire. No joke, don't use them. You can use film type, or motor-start capacitors.

Paul (author)Mr. Apol2011-06-06

Well, I know this, I believed you. I just wasn't getting anything else to work so I gave it a shot and it worked temporarily. I have a big box for it and i'm outside with it so its all good. (author)Mr. Apol2011-06-05

Thanks, I just pulled about 5 film caps from a CRT board so I should be set

gunner21 (author)2011-04-23

i have a 12 V ignition coil , can it run off of 120V AC

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