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Home made Capacitors for a SGTC! (yes, Again...)

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LAN_403

Muttyfutty!

Sat Sept 04 2010, 04:51AM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

Hi!
Well, Ive done some searching on Google and In the forums but I haven't yet found my answer...
Instead of using Aluminum foil/sheet or copper in the capacitor, Could I use galvanized steel as I have loads of the stuff.
Actually, I was under the impression to stay away from steel in a TC, due to high losses at high frequency,
but does this apply to the caps?
Maybe I should just stick to Al Foil?
Sorry if its a stupid question...
Thanks,
Mike

ZakWolf

Sat Sept 04 2010, 06:13AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

a capacitor is just and insulator between negative and positive, so all you need is tinfoil on the out side salt water on the inside with a wire from each , BOOM you have a capacitor. Also Google linden jar :) good luck

Muttyfutty!

Sat Sept 04 2010, 08:55AM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

Thanks, but I was talking about flat caps, not salt water ones.
I would prefer to avoid al foil because its hard to shape properly, and prone to crinkling, which would produce corona loss.
The steel I have is fairly thick, so no rips or tears to reduce efficiency...

Herr Zapp

Sun Sept 05 2010, 05:45AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

MF -

With flat-plate capacitors, the corona problem will be far, far worst at the sharp edges of the metal plates, compared to corona generated by any wrinkles in the surface of the material itself.

Your galvanized steel plates will "work" fine in a stacked capacitor, but how will you make your electrical connection to each plate without increasing the thickness of the plate? Cutting aluminum foil plates with integral connection tabs is much easier than cutting the same shape plates out of galvanized steel sheet.

Herr Zapp

Muttyfutty!

Sun Sept 05 2010, 03:13PM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

Oh dear, I was really running out of ideas for my cap, as the price of 'good' caps and shipping is far too much I can afford.
Is the loss significant, or should I reach in my bank account and buy some 'Popper' Capacitors.
What would you recommend?

To connect the plates I was planning to cut mall 'tabs' out of aluminum foil and sandwiching them on the edge of the steel plates.
Thanks again,
mike

Herr Zapp

Mon Sept 06 2010, 12:45AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Mf -

I'd recomend you try aluminum foil first.

If you look around, you can find "commercial heavy duty" aluminum foil that's about twice as thick as regular "household" Al foil, and is much more resistant to tearing, yet still very easy to cut with ordinary scissors or a razor knife.

I don't think your "galvanized steel plates with inserted aluminum foil connection tabs" is a very good idea because of the difficulty of achieving a good, low resistance connection between the foil and the plates.

What input power level are you considering, and at what voltage?
What type of dielectric material were you planning to use?
A conservatively designed and carefully-made flat plate capacitor can work well at lower power and voltage levels, although they are quite laborious to assemble.

Herr Zapp

Muttyfutty!

Mon Sept 06 2010, 01:39AM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

Ok, Thanks, Ill stick to Al foil. Unfortunately nowhere I can find seems to have the thicker stuff..
The dialectic I was planning to use is 1/16" acrylic. as I can find Large sheets for under 10Pounds.

I'm not too sure what power level my coil is at, as I am not very experienced, but I am using a 15/30 NST, and a 4x20" Secondary
I assume its considered small/medium?

I have had bad experiences with the "3.5nF 80KV homemade cap" On the HV wiki.
I experienced constant flash overs, probably due to a too large plate size, but because I glued It together, I was unable to resize the aluminum foil electrodes.
Ill retry Them soon...
Thanks, I have taken all you said into account; What Caps would you recommend I use?
Homemade flat, Rolled, or purchase some?
Regards,
Mike

genious 7

Mon Sept 06 2010, 02:30AM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107

I have had bad experiences with the "3.5nF 80KV homemade cap" On the HV wiki.

I also had bad experiences with them, but I resized the plates (2 cm smaller in every side), and got it working.

Muttyfutty!

Tue Sept 07 2010, 02:25PM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

Yes Thats what I was planning to do, Thanks anyways! :)
Does anyone know if these rolled caps are better (more efficient) than the flat ones?

Adam Munich

Tue Sept 07 2010, 08:54PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

What about keeping your capacitor under oil to eliminate corona? That could possibly work, and mineral oil is pretty cheap.

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