Picture of DIY Capacitor
In this Instructable I will be making one of the easiest high voltage capacitors that I know of.....

WARNING High voltage electricity can cause death and serious injury.I do not recommend that anyone work with high voltage power sources unless they know how to do it safely.
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Step 1: Getting the materials

Picture of Getting the materials
You will need:

1.A long screw
2.Some tin foil
3.A 2L bottle
4.some salt and hot water
5.Electrical tape

The first thing you do is get the cap and put a big screw in it.

Step 2: Tin foil time

Picture of Tin foil time

Now take 15inches of tin foil and fold it in half :)

Step 3: Almost done!

Picture of Almost done!
Now tightly wrap the foil around the bottle and tape it in place.It is very important that it has almost no air bubbles between the plastic bottle and the foil.....

Step 4: That wasnt so hard was it? :)

Picture of That wasnt so hard was it? :)
Ok ... Now if you want you can tape a wire to the foil and then wrap the whole bottle in electrical tape (thats what I did)

Fill the bottle with water and over saturate it with salt,baking soda
(Right now I'm trying water and vinegar 50/50 mix)


These capacitors work great in small Tesla coils and they make a very loud noise

Have fun and be safe
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How can we control the voltage of these? Building a generator and I want it to go no higher or lower than 230V (The voltage that UK homes get).

Use a resistor. Measure the voltage it produces. Invert the current to ac, run it through a transformer of the voltage you measured to 230v. Charge it for the same amount of time every time.

I don't think capacitors can be used for that, they supply one shock not continual voltage like a battery.
GeoK5 months ago

If you really want to make something REALLY dangerous manufacture a few capacitors utilizing 55 gallon poly drums with the entire outer surface covered with heavy duty aluminum foil very similar to this arrangement then sprayed with truck bed liner for insulation. Use a 30 foot coil of 1/2" soft copper tubing for your internal terminals for some major current carrying contact area with the 55 gallons of super saturated saline solution in each of the 2 barrels. Pick up a 500 foot roll of 12 awg copper wire and strip it with a sharp blade by tying off one end and walking down the line while holding the blade at the appropriate angle to efficiently remove the insulation at a decent pace. Wrap 5 50 foot lengths of your now bare 12 awg wire around the exterior aluminum foil covered drums in a helical ascending fashion then twist the 5 tails together tightly for a good 4 inches or so to produce a connection point with some respectable high current carrying capacity. 50 pound bags of water softener salt can be purchase extremely cheap to produce your SS salt solution. The roll of 12 awg wire costs $59 at lowes, the 60ft roll of copper tubing costs $139 and the salt somewhere around $10 bucks per 50lb bag. If you can scrounge up the poly drums free you can assemble a pair of far beyond lethal terminator caps for under $250 bucks! Charge them up with a pair of old 1500 watt microwave oven transformers (The good ones back when they were still called Radar Ranges) and you could set up a truly maniacal active burglar alarm system! Salvage the high voltage diodes from the microwaves as well of build a full wave bridge rectifier from high voltage diodes to make use of both ends of the AC cycle, waste not want not. Now simply run one wire to an expanded steel mesh fronting as an innocent a door mat and securely fasten other to the doorknob with the activation/detonator switch installed inside the door jam set to fire it off should anyone try to slip a credit card through the door jam to circumvent your lock. With one barrel charged positive and the other charged negative for a 16,000 volt DC combined potential difference at that capacity the perp would most likely explode violently when his now airborne corpse was determined to be the path of least resistance for 50 cents worth of electricity unleashed in a millisecond or two! Once it's all over simply pick up the mesh mat and remove the 4 AWG connecting leads tossing it down in the basement with the barrels and the rest of the gear the call the coroner. It will appear to have been an apparent divine intervention where God himself struck down the intruder with a bolt of lightning! That is probably pretty close to what the event would look like even if the nosy neighbors actually witnessed it unfold, especially at night! In any event, this hypothetical (though technically feasible) instructional ranting is only a work of fiction for your entertainment. Nobody in their right mind should never even think about assembling such an evil contraption even if well versed in the black arts such as something on this massive scale and level of mental illness. In the most likely event you incinerate yourself or a loved one while attempting to build this or any variant I shall not be held liable... Though I will truly enjoy the gory video in the event your equally twisted friends upload your demise on World Star Hip Hop!

rocket_man4 years ago
Alright stupid question but about how much voltage could one of these charge up to

This is stupid alright. Not in the sense that you are stupid, but in the sense that people shouldn't mess around with these kinds of devices without knowing how they work. I read stuff about people here playing with flybacks and what not. These things can kill you. High voltage is not a toy, and the knowledge one gains from plugging a TV set into the mains outlet is not enough for building high voltage devices. That's why building a high voltage cap. and afterwards asking questions such as "what will the voltage be" is stupid.

Now, to give an answer. Imagine a jar that you can put stuff in. A capacitor is much like a jar, where you put charged particles in. Your question reads somewhat like "how much stuff can i put in my jar?". Well it depends on how hard you push, doesn't it? The equivalent of the applied force to your imaginary jar is in the electrical case the voltage. Voltage is the measure of how hard you push, not how many charged particles exists in a location (how much stuff you've crammed in so far). So the more electrical particles you want to cram into you jar, the harder you have to push. Now the reverse is true, the more electrical particles you've put in your jar, the more electrical "push" your jar can excert on it's surroundings.

In general though, a capacitor will charge up towards the same electrical potential as you apply. If you apply 3V and wait long enough time, the capacitor will charge up to 3V. If you apply 30 kV the cap will (in theory) charge up to 30 kV.

However, the dielectrica (the insulator between the electrodes) can only keep the charges separated below some certain threshold voltage, over which the particles will simply go through the insulator, breaking the barrier and destroy your cap. This is how sparks are made. Up the voltage above a threshold, and you will get a spark.

The other thing is that just as it takes time to fill a jar, it takes time to fill a cap. It can take very different time to charge/discharge a cap depending on different factors (resistance in wires, capacitance of cap), and strictly speaking, the voltage will only approach the applied voltage, but never actually reach it.

If I didn't make sense above, this only means that you shouldn't make any more lethal electrical devices prior to reading a book on the subject. If you do understand these things, and spotted some error on my behalf here, please reply and correct me.

PS. In school (master level electrical engineering) an electrical safety specialist convicingly showed how it is possible to get yourself killed with < 9V, given sufficiently bad cirumstances involving rain and jewelry and a weak enough heart, if I remember correctly DS.

suttiwit6 months ago

What is the screw on top for? And how do I charge the capacitor? Where is the negative and positive terminal?

whats the baking soda for?
neohearted made it!8 months ago

I have made it...It works perfectly..

Dude this just doesn't work i substituted the expensive table salt for driveway salt replaced the plastic bottle with a glass bottle I just happened to have after I did it all I was left with a worthless bottle of saltwater I tried charging it with a 9 volt then a dc power supply then a high voltage low amperage grill igniter and nothing no spark no reading on the meter nothing
What did I do wrong they make capacitors with glass layers?

The reason your glass bottle capacitor didn't work is most likely because glass bottles are fairly thick. The thinner the insulator between the 2 terminals the more capacitance. The plastic bottle is thinner so you should use a plastic bottle next time. However I don't think it is a problem if you use driveway salt.

hawks882 years ago
Would using copper foil make it better?
not really, to increase capacitance you either increase surface area or decrease the distance from the "plates"
Can you trickle charge a capacitor? For example, from a small solar panel? If I have a 400mf Capacitor, can it take varying trickle charges in and still reach its full potential?

Or, would I have to hook the panel up to a small 6v battery, and funnel the voltage into the capacitor that way? What if the battery only has 100mah, is that relevant?
C= (dielectric constant) x (area / distance)

What Area do you use and what distance?
Is it the diameter of the bottle?
jabujavi2 years ago
How many farads is that?
monney953 years ago
Why is there no internal foil layer like in a typical leyden jar? I have made one and will test but am not sure if it will work for this fact.
The saltwater (a conductor) acts as the internal foil.
what is the capacity of this leyden jar?
nice project though.

polishdude6 years ago
How do you charge the capacitor up?
High Voltages, Televisions work decently, high voltage transformers, or even a van de graph generator. But be very careful, if you build it larger than a masonry jar it can get dangerous and possibly deadly. Do not play around with electricity if you don't know what your doing.
jakesllama6 years ago
you know what im thinking? worlds strongest electromagnet ever! thanks for the compaciter i will try to make it!!
 The strongest ever is over 500,000x stronger than the earth's.
The strongest ever has been recently created using graphene inside a lab environment measured at about 300 telsas. To put this into relativity, a really strong magnet, one of those rare earth, or neodymium magnets are about .7 teslas. Read up on it here: so 10 Million at this point!
worlds strongest? your going to need a lot of 2lt bottles!!!!!!
still best to buy one 10X smaller 
liny jakesllama5 years ago
I wouldn't recomend it but you could try. To make the world's strongest, you will need to beat the Navy's Gaussian guns (railgun and coil guns) with capacitors that can vaporize you. After that, you will need to beat the actual strongest (i think) electromagnet that can (more or less) defy gravity (it makes apples and stuff float, even water, just like an anti-gravity space). As a side note, the electromagnet is bigger than a house.
when i saw this i thought. that looks unreliable and overly dangerous, and sketchy, i give a forewarning i would not do this, and i am tring to build a tesla coil. so i am being nice and revving a friendly warning.
conb34 years ago
If you add lemon juice to the water will it make it more conductive ?
Crtek4 years ago
could anyone tell me if the screw should be touching the water inside the bottle or not. i can't seem to find this info anywhere

oh and how would one connect multiple capacitors like this in series?
It should be. As for connecting them in series, connect the positive to the negative, then the positive of that capacitor to the negative of another etc. In short, foil to nail, foil to nail. As long as you don't connect the same capacitor to each other twice. By the way, why connect them in series? One is already powerful. People would usually connect them in parallel, but of course, that depends entirely on the use. What are you planning to do with them anyway? Just so that I can satisfy your questions.
i need them for a tesla coil
so would that mean i need to connect them in series or in parallel?
series, for a tesla coil you want as high a voltage as possible (to prevent over-voltage) and as little capacitance as you can (to keep the frequency of discharges through the spark gap high) unless your not using a spark gap coil, in which case i have no idea.
A Tesla Coil? Sorry, I don't have experience building tesla coils. There are instructables floating around that could have people that can answer your question. Or you can post the question as a question in the first place.
techno guy4 years ago
Is the bright spark in the last picture done with static electricity or with high voltage ac or dc? I made my own capacitor, its smaller but its awesome if you connect it with high voltage ac (500+ volts) like from a flyback it makes some awesone sparks and you could sometimes make small corona discharges.
you cant charge a capacitor with ac, can you?
Because it is alternating, it will charge in one direction, then when the current reverses it will be discharged.
If you want to use an AC source you need to rectify it. The easiest way to do that is to use a (high-voltage) diode to only allow current to flow in one direction, thus preventing discharge.
techno guy4 years ago
To make a capacitor bank with these, what would be better, hook them up in parallel, or in series?
sorry didnt read well, what would you be using this for? if you want to increase the voltage, than do it in series, if you want to make it last longer do in parallel
With capacitors, in series reduces capacitance using formula (c1*c2)/(c1+c2), in parallel increases capacitance, so in parallel would be better.
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