Tesla's power supply

[Guest]

So you're telling me i can easily put 4.5kv on my little Aerovox microwave cap that's rated at 2.1kv and 1.14uf?

Thats amazing!

[Electrotek]

So you're telling me i can easily put 4.5kv on my little Aerovox microwave cap that's rated at 2.1kv and 1.14uf?

Thats amazing!

Yes, I was pleasantly amazed too. I'm using them now with my NST. When connected in parallel they add up fast.

[barbosi]

Aren't those microwave capacitors having an internal resistance connected in parallel?

This is what I found... If you discharge them fast enough after charging, it might not be an issue.

[Electrotek]

Aren't those microwave capacitors having an internal resistance connected in parallel?

This is what I found... If you discharge them fast enough after charging, it might not be an issue.

I'm not sure. The instructions inside the cabinet do say to discharge the cap before servicing. But like you say, discharge them quickly enough. They've been working alright in my EV Gray circuit tests. They produce the same plasma effect as my larger caps, it's just not a big a plasma because the Joules are lower.

[Guest]

Inductance and Resistance of Capacitors

Each capacitor has some inductance and resistance and when you connect them these values unfortunately add. That's why it's always better to have one large capacitor than many in parallel or series, but the values are usually so small that they go unnoticed until you perform massive disruptive discharges at radio frequencies, or stack hundreds together.

[cody]

Thats great news about the microwave capacitors, thanks Electrotek! I got 4 free microwaves in just this past week, and had been trying to figure out a way to use those caps, with this info about their break down point i will definatly be using them. Thank you

PArAd0X, i didnt know that about water, interesting That link said that it only holds up for a little bit before it starts to conduct, so thats probably the reason why its not usually used. But still.... learn something new every day, thanks!

[Guest]

I was looking into some homemade capacitor variations but the results are all depressing. For something that I can make weighing 30 kilograms the equivalent can be bought in the size of a can. So i will probably be saving up for one of those nice 50uf 5kv caps on Ebay.

The only other homemade solution that could be viable to me is to combine 2 dielectrics like water and glass. One for its dielectric constant and the other for its high breakdown voltage.

[cody]

Yea, i see your point. I didnt think it would take that much and buying one is looking much easier than making one. Im still planning on making my tank cap because that is very low capacitance and i want it to be a variable capacitor. Or i might be able to use the variable cap i have and just dunk it in transformer oil. Problem is that i cant source any yet. For anyone who hasnt seen this page yet and is interested in making HV caps, this is a great page.
High-Voltage Capacitors, make your own! HV
All kinds of great info there.

[Electrotek]

Yea, i see your point. I didnt think it would take that much and buying one is looking much easier than making one. Im still planning on making my tank cap because that is very low capacitance and i want it to be a variable capacitor. Or i might be able to use the variable cap i have and just dunk it in transformer oil. Problem is that i cant source any yet. For anyone who hasnt seen this page yet and is interested in making HV caps, this is a great page.
High-Voltage Capacitors, make your own! HV
All kinds of great info there.

Thanks for the link; I enjoyed reading it. However, polypropylene wasn't listed in the dielectrics chart. Most people haven't caught on that this plastic has a puncture voltage of a few kV per mill, rather than a few mills per kV, as with polyethylene.

[Guest]

Properties of Mylar

Mylar looks pretty impressive @ 7.5KV/0.001". I think that's almost 300KV/mm
Why isn't this being used more often then... or is it some sort of mistake.

[cody]

mylar is a very popular material in manufactured capacitors. If you look at the little non electrolytic caps in electronics you will read on them either mylar or poly for the material used to separate the plates. My only issue with using a plastic for dielectric material is that if you have a flashover, it melts through the plastic and then the capacitor is shot. Where as if you are using a material such as oil or metalic film caps, its self healing, so if you accidently exceed the voltage rating and have an arc, the cap will still be good.

[Electrotek]

mylar is a very popular material in manufactured capacitors. If you look at the little non electrolytic caps in electronics you will read on them either mylar or poly for the material used to separate the plates. My only issue with using a plastic for dielectric material is that if you have a flashover, it melts through the plastic and then the capacitor is shot. Where as if you are using a material such as oil or metalic film caps, its self healing, so if you accidently exceed the voltage rating and have an arc, the cap will still be good.

I haven't tried mylar, but it'll be easy enough. And mylar is usually aluminized on one side, so there's one electrode already. Thanks for pointing this out. And I agree with your assessment of oil, for self healing. That's why I like to use both oil and plastic. Although oil does require a much higher plate separation distance. Is there a ready source of mylar which is comparable in price to the sheet protectors? You can get 50 of them at WalMart, at 1.4 mills, for around $4.

[Guest]

Then how about manufacturing a mylar capacitor, then submerging it in oil to prevent flashover and coronae on the sides?

[Electrotek]

PArAdOX: That would probably work. With metalized mylar I think one strip would have to be narrower than the other, to prevent flashover at the sides.

[Guest]

I found this page pretty useful to me with cap calculations:
Cap Calculator
and it has a few plate layout ideas too