Homemade plate caps

[billybob]

I repeated the same message twice apparently

 

[billybob]

I would rather use glass than plastic

I haven't figured out how to make the glass less apt to break from moving or arcs though.
My glass cap has lost a layer or two from shattered glass.

 

[shortbus=]

My glass cap has lost a layer or two from shattered glass.

Glass in a jar or bottle shape is stronger than a flat plate shape. While not a Tesla coil, the Whimshurst machines I made used empty Yoo-Hoo bottles. Thin brass sheet on the bottom and side of the outsides, and Daisy brand B-Bs on the inside.

Back to your original post for a minute. When you said there was corona, was it just fringing on the foil edges or did it actually spark over from foil to foil?

 

[billybob]

Glass in a jar or bottle shape is stronger than a flat plate shape. While not a Tesla coil, the Whimshurst machines I made used empty Yoo-Hoo bottles. Thin brass sheet on the bottom and side of the outsides, and Daisy brand B-Bs on the inside.

Back to your original post for a minute. When you said there was corona, was it just fringing on the foil edges or did it actually spark over from foil to foil?

Interesting I thought plates were more effective, good to know. What do you mean about the “B-Bs” was that the conductor on the inside?
the room smelled of ozone seconds after I turned it on. The foil would be surrounded by little purple fringes, but as I turned up the variac and if I opened the spark gap past a point the plates would arc.

 

[shortbus=]

Yes the BBs made the inter conductors, it's an old way of doing it with a small necked bottle.

The fringes I wouldn't worry too much about, spark over yes worry. But when this is done and all correctly tuned most of the problems should go away. This tuning is what you have the Variac for, starting at lower voltage levels to get things "correct" before full power. And any time you make a lot of sparking, ozone is a by product.

 

[billybob]

So Finally made the Cap. Probably took more time and money than it was worth. Cast me about 20 dollars in plexiglass and epoxy glue. Took me around six or seven hours cutting, sizing, placing and glueing combined. The results are decent, no visible corona wisps, but I do get arcs at around 10kVolts. You guys were right about glass being better, the 18 plate plexiglas cap measures 2nf. The glass cap 5 layers is around 4nf. I was able to tune the tiny tesla coil by just increasing the tap on the furthest turn, but still a little unstable. Is there a way I can insulate the plexiglas cap without oil? Kinda messy.
I think next time Im only gonna do glass. I can send pics later I got school to finish.
Thank you all for the help,
Ben
By the way I also just built a voltage multiplier that can deliver 7 inch sparks.

 

[shortbus=]

Keep at it! Personally I'm a "static electricity" guy. My home made Wimshurst Machine will make continuous 2 1/2 to 3 inch sparks with just slow hand cranking. If you go too fast though it starts sparking between it's foil segments. Got the stuff to build both a Van de Graff and a Dirode but have too many other projects to finish before starting new ones.

 

[billybob]

Sorry I never posted a picture. Well here it is.....
As well as the voltage multiplier I mentioned earlier. Pretty proud of the multiplier.

 

[rjenkinsgb]

Veri nice!

Just a suggestion for the next cap version:
I'd try greasing either the plastic/glass sheets or the foil (both sides) for the caps with eg. vaseline or silicone grease, and clamp the plates or put them under a heavy weight for a day or so, to try and eliminate all air spaces.

That should give a significantly higher value capacitance, than dry foil that is not physically tight against the dielectric.

 

[billybob]

Veri nice!

Just a suggestion for the next cap version:
I'd try greasing either the plastic/glass sheets or the foil (both sides) for the caps with eg. vaseline or silicone grease, and clamp the plates or put them under a heavy weight for a day or so, to try and eliminate all air spaces.

That should give a significantly higher value capacitance, than dry foil that is not physically tight against the dielectric.

Thank you!
Well I’m sure I will be attempting this again sometime, so yes I will do that.

 

[billybob]

I think this thing has become an addiction now...
I subconsciously wandered into Dollar general and ended up with nine 8 inch by 6 inch glass frames as well as some more glue.
Guess another cap is in the making.

 

[billybob]

Veri nice!

Just a suggestion for the next cap version:
I'd try greasing either the plastic/glass sheets or the foil (both sides) for the caps with eg. vaseline or silicone grease, and clamp the plates or put them under a heavy weight for a day or so, to try and eliminate all air spaces.

That should give a significantly higher value capacitance, than dry foil that is not physically tight against the dielectric.

Can I grease them with mineral oil?

 

[rjenkinsgb]

Yes, that should work, as long as the clamps are never released; it will just be messier.

Using a grease would also "glue" them together to some extent so they were less likely to separate.

The idea is to permanently exclude all air - any air between the metal and separators will lower the capacitance & if they come lose and draw in more oil it will also reduce the value, as would using grease but not clamping them hard enough to squeeze out any excess.

 

[billybob]

Made another plate cap with 5 glass plates and four 6 inch by 5 inch foil and measured almost 6nf with a compression plate it had mineral oil in between. That one cracked and here’s a picture.
So I then made another glass plate cap that is probably my favorite now.
it has 7 glass plates and two pieces of plexiglas glass on either side it measured 11 nf!

 

[Beau Schwabe]

A couple of things ...
- Round your corners
- I have used 2 inch adhesive tape just fine without the messy glue (when you are in the kV range gaps between the foil are less of an issue)
- thinner is better, I have used polypropylene from the side walls of kittly litter containers for making 50kV caps (leave about a 1/2 inch perimeter from the foil to the edge of the plastic.)

Reference: Marx Generator using such caps ...

 

[billybob]

Well I was running the cap with my 10k OBIT and while there was little to no Corona it arced. When I looked over it I saw a tiny burn mark. SUPER FRUSTRATING!! Yet another cap goes to the trash. I bairly had it a day.