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!

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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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rocket_man3 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 days 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!2 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.

hawks881 year 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?
jabujavi1 year ago
How many farads is that?
monney952 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.

polishdude5 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.
jakesllama5 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.
conb33 years ago
If you add lemon juice to the water will it make it more conductive ?
Crtek3 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 guy3 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 guy3 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.
Crtek3 years ago
by the way...i've seen loads of capacitors made from a can (Al) on the inside and Al foil on the outside
are those better in anyway or can i just make the water kind?
thanks for your answers
Brian Wall4 years ago
wats the srew for?
its the contact. if u touche the the scw to the aluminum foil with a wire it sparks
micronxd6 years ago
nice design! I never thought of using a bottle! I've only made a simple one out of paper... nothing like this!
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