Will a Leyden Jar Store AC Current?

[Fischer777]

Okay, I was planning on building a Tesla coil for my (high school) physics class. For the high voltage capacitor I was planning on using a Leyden jar, however, after doing some research I only found references to it being used to store an electrostatic charge. Thus, my question is, can a Leyden jar be used to store a high voltage AC current? Or should I stick with the more commonly used saline-in-a-plastic-bottle capacitor?

 

[Phrak]

This is for the primary side of a Tesla coil, right? If so, you are storing DC electric charge.

A Leyden jar stores a fantastically tiny amount of charge. So does the salt water in a bottle. It's just a variation of a Leyden jar. Is the saline in a bottle trick really what your Tesla coil plans call for?

 

[vk6kro]

This transformer operates at about 15000 volts AC. That would be OK for a Leyden Jar, but the capacitance needs to be about 0.0235 µF which is a lot more than one Leyden Jar (which would be about 500 pF) could produce.

I found this website:
http://www.richieburnett.co.uk/parts.html#schematic
which gives a way of making such a capacitor.
They use 8 parallel strings of 16 0.047 µF 1500 volt capacitors in series.

 

[Phrak]

This transformer operates at about 15000 volts AC. That would be OK for a Leyden Jar, but the capacitance needs to be about 0.0235 µF which is a lot more than one Leyden Jar (which would be about 500 pF) could produce.

I found this website:
http://www.richieburnett.co.uk/parts.html#schematic
which gives a way of making such a capacitor.
They use 8 parallel strings of 16 0.047 µF 1500 volt capacitors in series.

Since I posted, I've also done some internet poking around myself. The 15KV value comes from a standard neon sign transformer. A table top Tesla coil could be take much less voltage and require less capacitance.

A polypropylene soda bottle is a better dielectric than a glass bottle and is a lot thinner. (But is the dielectric strength good enough?) A few soda bottles filled with salt water and wrapped in aluminum foil or sitting in a bucket of salt water might work just fine for a school science project.

Edit: I'll have to retract some of this. The dielectric constant of Polyethylene Terephthalate Polyester (PETP), used to make soda bottles, is 3.0 at 1MHz. (It's dielectric strength is 17KV per millimeter).
By comparison, the dielectric constant of silica glass is about 6.0 at DC. I don't know about glass at comparable frequencies.

 

[Phrak]

So I found a 1 liter pepsi bottle. It's only 12 mils thick! At 5.2 KV breakdown, the most you'd want to put across it would be about 3kV.

 

[Fischer777]

The capacitor is on the primary side. However, the neon sign transformer I plan on using only produces 10Kv at 30 miliamps, which I assume is probably enough (the secondary is only 18 inches tall and about 2 inches in diameter). I was informed that a similar Leyden jar capacitor to the one I'm using can hold up to 3 joules of energy (it was specified as a gallon mayonase jar, however, I only used a standard sized jar). I did not do the math to check this, however, and if the walls are significantly thiner then it may be substantially less. I also was informed from this same source that glass Leyden jars are a bit more 'rugged' than plastic (being able to take more current and alternating at that), and that is what made it my first choice.

 

[whocouldshebe]

To charge from AC you need a one-way High Voltage Diode 5-10kv in-line to stop the alternating current from returning. I say 5kv because at 10kv only half the volts will becoming backwards back out of the jar at frequency.