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.

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Step 1: 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.

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cgosh1 year ago
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.

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.

masonmilby2 years ago
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)  masonmilby2 years ago
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?

Is this a good capacitor also ill use ac 120v
Mr. Apol (author)  masonmilby2 years ago
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!

How long do you mean?
Mr. Apol (author)  masonmilby2 years ago
Basically the charge can last for days or weeks. You can short it out with an insulated screwdriver, but for goodness sake be careful.

what exactly do you expect to happen when its shorted with a INSULATED screwdriver?
Mr. Apol (author)  houdini01182 years ago
You discharge the cap without shocking yourself.

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)  houdini01182 years ago
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.

And would this one work?
Mr. Apol (author)  masonmilby2 years ago
That would be just about ideal.

will any ignition coil work
Mr. Apol (author)  masonmilby2 years ago
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.

How do I measure the output voltage of an ignition coil
Mr. Apol (author)  masonmilby2 years ago
Lacking an expensive high voltage meter (which I don't have) you have to estimate voltage based on spark length:


I got a 1 3/8 inch spark length how many volts do you think is coming out of it?
Mr. Apol (author)  masonmilby2 years ago
An inch of spark is ~20 KV, so 1.375 inches would be around 28 KV or so. Just as a rough estimate.

sevise2 years ago
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)  sevise2 years ago
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 Mr. Apol2 years ago
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)  sevise2 years ago
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.

bswt3 years ago
how did you wire the film capacitor to ac power did you put it across the mains ?
Mr. Apol (author)  bswt3 years ago
See the article and diagram here:

jj.inc3 years ago
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.inc3 years ago
You need a capacitor to buffer the coil and cut down on that overheating.

Paul Mr. Apol3 years ago
buffer? To me it doesn't look like it does anything at all
Mr. Apol (author)  jj.inc3 years ago
I have run my ignition coil (with capacitor) for minutes and it never gets hot.

Paul Mr. Apol3 years ago
ok, so it is on the 120v end right?
Mr. Apol (author)  jj.inc3 years ago
See the diagram here:

Paul Mr. Apol3 years ago
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.inc3 years ago
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 Mr. Apol3 years ago
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.inc3 years ago
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. Mr. Apol3 years ago
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. Mr. Apol3 years ago
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.inc3 years ago
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 Mr. Apol3 years ago
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.
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