leyden jar help

[dstich]

i have been trying to make a lyden jar and i have been having a lot of problems getting the foil on the inside of the jar can anyone give me some ideas on how to do this

 

[Russlk]

It would be simple if you could get your hand in it, so it must be a small jar? How about painting the inside with conductive paint? You could pour the paint in and swirl it around.

 

[panic mode]

what size jar? when i was kid, i used to make small ones from plastic containers (package for film rolls). i would solder wire to piece of sheet metal. to prevent wrinkles of the electrode, i was using second container as a sleeve (top and bottom cut out, narrow slot cut out along the side to compensate for diameter change). then press fit it with a piece of foam or cork. the wire would come out through cup and end in a small loop. so the sandwich would be outer electrode, container, inner electrode, sleeve, and compression material like foam.

 

[dstich]

it is a fairly large jar about 1 qt I ques what hapens is i put the foil in and then try to tape or glue it on but i can never get it to stay i can barley fit my hand in the jar o and for Russlk i have some matelic paint i so i tried painting a small area and measuring the resistance and the resistance was very high over even a short distance like .7 mega ohoms over a distance a bout a inch

 

[panic mode]

then just try salty water and be careful to avoid spills :wink:
as i wrote before, i had poor results with foil so i was using
sheet metal for inner electrode. if piece of sheet metal was flat,
it will tend to unroll and stick to inner side of the jar.
one just need to secure it a bit, (jam in pile of newspaper,
marbles, nuts and bolts, rocks, ...). it's just crude capacitor,
not Swiss watch...

 

[Oznog]

I did it a long time ago by rolling up the foil, spraying 3M spray adhesive inside the jar, put the rolled up foil in there, touch the loose end against the side and then carefully unroll it all the way around.

Note "tight" is actually bad because any tension will tend to pull the foil away from the wall. It's a matter of sticking down the loose end of the roll, then running your finger up and down to tack down the next 1/4" of the roll while carefully avoiding any contact between the rest of the roll and the jar's wall. Then another 1/4" and so on.

The foil on the outside can also be spray adhesived down. But you want to add 2" wide clear packing tape on top of that to keep the foil from pulling away, keep the foil from getting torn up, and to provide some degree of insulation. It's not like that makes HV safe to touch, but it will keep the corona down if you're doing a Tesla coil.

 

[dstich]

i got the foil inside by by making a tube from a 2 liter soda bottle a little larger than the inside of the jar then i wraped foil around the tube then i folded the tube put it through the mouth of the jar then let it unfold so it pressed the foil agenst the inside of the jar but now i get a smaller spark from the large leyden jar than i get from my little film canester one can anyone tell me why this is does it just need a LOT!!! of charging or what

 

[Nigel Goodwin]

i got the foil inside by by making a tube from a 2 liter soda bottle a little larger than the inside of the jar then i wraped foil around the tube then i folded the tube put it through the mouth of the jar then let it unfold so it pressed the foil agenst the inside of the jar but now i get a smaller spark from the large leyden jar than i get from my little film canester one can anyone tell me why this is does it just need a LOT!!! of charging or what

Capacitance is inversely proportional to the spacing between the plates, the glass jar will be much thicker than the film canister. It's also dependent on the insulator between the plates, but I've no idea of the reletive advantages of glass or plastic?.

 

[dstich]

i would gues that glass and plastic have about the same insolating qualaties so if i get what your saying because the glass is thicker it will take more charging to create the same charge??? os did i screw up in making the cap some how

 

[Roff]

I did a little searching and found that film canisters are made of high density polyethylene, which has a dielectric constant (Er) of 2.65. Glass Er varies, depending on the type, but it appears to be around 7.5. Capacitance is directly proportional to the area of the smaller plate and to the dielectric constant, and, as Nigel pointed out, inversely proportional to the distance between the plates.

 

[dstich]

so if i understand right the further between the plates the less capacatence??? sory if im not getting this right im kindov a newb to electronics

 

[Roff]

so if i understand right the further between the plates the less capacatence??? sory if im not getting this right im kindov a newb to electronics

Yes. You will get the most capacitance with a big (tall, large diameter), thin, glass container. If you use a film canister, it has to be 1/3 the thickness of glass if the other dimensions are equal (because of the differences in dielectric constant).

 

[dstich]

thank you for all the help and Ron H good luck with your dog problems

 

[Roff]

thank you for all the help and Ron H good luck with your dog problems

I've decided to follow the dogs home and piss on their owners' lawns. :twisted:

 

[Oznog]

So what did you want to make the Leyden jar for again?
The best construction is very different for high and low frequencies for example.

 

[dstich]

I didn’t really make it for any particular use just to play around with but I would like to store a large charge with them

 

[Roff]

I didn’t really make it for any particular use just to play around with but I would like to store a large charge with them

You can store a (relatively) large charge if you have a high DC voltage. I calculated the capacitance of a quart glass jar to be about 2nF, +/-50%. Since charge Q=C*V, more voltage will give you more charge. The breakdown voltage of a glass jar 1.5mm thick (I don't know how thick they really are) is on the order of 12kV. So theoretically, you could store 24 microcoulombs on a quart Leyden jar. You can store a lot more charge on an electrolytic capacitor, but the high voltage is what makes the Leyden jar interesting.
This is the results of several SWAGs, so it's worth what you paid for it. :lol:

 

[Dr.EM]

Kind of on topic, what do you think the dielectric constant of clingfilm is? I wondered if you could make a large foil cap with domestic tin foil and clingfilm :lol:

 

[Roff]

Kind of on topic, what do you think the dielectric constant of clingfilm is? I wondered if you could make a large foil cap with domestic tin foil and clingfilm :lol:

According to **broken link removed**, the dielectric constant is 3.0 to 6.0. Pretty sloppy, but better than zero to infinity.

 

[dstich]

would that be simaler to press-and-seal wrap or would that be a diffrent thing
you could make a cap by aranging the foil and the wrap like this corect???
-------------------------
++++++++++++++ if the foil is --- and the wrap is +++ it would be just
------------------------- like the leyden jar but flat