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TDK Ceramic "Doorknob" Capacitors For a Tesla Coil

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jpsmith123

Mon Sept 14 2015, 04:28PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

Has anyone ever used TDK ceramic doorknob capacitors (UHV series) in a spark gap type Tesla coil?

From the data sheet, they seem to have a relatively low dissipation factor, but before I spend money on them, I'm wondering: Do they heat up very much in a Tesla coil primary circuit? And if they do, do they heat up enough to make it go out of tune or anything like that?

Sulaiman

Mon Sept 14 2015, 06:02PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

2.5% dissipation ceramic capacitors worked in a sgtc (Panasonic MDU)
upgrading to 0.1% pp foil/film/foil made a big improvement. (Arcotronics/Kemet A.72)
That was at c220 kHz (unsure/forgot)

ceramic capacitors are a heat dissipation/generation winner
quite lossy but can run relatively hot vs.
pp foil-film-foil generate much less heat, but die at 85C

EDIT: i.e. looks like a reasonable spec. to me but I do not know.

jpsmith123

Mon Sept 14 2015, 07:09PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

Thanks for the info Sulaiman. That at least gives me a reference point.

I think I'll go ahead and buy them...and if for some reason I'm not happy with them in that role, they should work nicely in a Marx generator.

Edit:
Apparently TDK UHV capacitors were used in this "Jolt" contraption (where they were used with a Tesla transformer to generate 1 MV pulses):

So I suppose they are a reasonable choice.

Hazmatt_(The Underdog)

Tue Sept 15 2015, 01:22AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I run TDK caps all the time and they work great.

They do not change over time, and do not short out your transformer. The MICA ones will short eventually and kill your transformer.
Most people shy away from them because of the price tag, usually $20 each, but the savings in construction and better
efficiency in current dumping to me is a plus.

Let's see those scrawny leaded CDE caps compete with M5 threaded buttons for current density! Not even close.

jpsmith123

Tue Sept 15 2015, 02:57AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

Thanks for the info. BTW that's a nice capacitor bank you've got there!

Hazmatt_(The Underdog)

Wed Sept 16 2015, 03:25AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Yea, and you know what, they're really not that hard to build either!

It's just 3 pieces of acrylic bonded together. If you polish the edges with a buffing wheel, it comes out really nice.

Then if you mount all the capacitors and torque them in, THEN glue, it comes out just fine. Try it some time!

jpsmith123

Wed Sept 16 2015, 04:17PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

I have a few novel ideas that I want to try. Maybe later I'll get a chance to make some kind of a drawing and post the details for discussion.

jpsmith123

Thu Sept 17 2015, 01:38AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Here's my proposed primary circuit: It's a Marx circuit, with the capacitors mechanically (and of course electrically) integrated into the single turn primary. I still have to figure out the hardware.

1442452889 1321 FT173096 Marx Tesla Primary

nzoomed

Tue Sept 22 2015, 11:53AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Does anyone know much about these russian ceramic caps on ebay?
There sees to be tons of old stock doorknob caps on ebay that were made in the USSR, but i dont know how reliable they are, but they also seem to be in rather low values, i need to make a 225nf bank for my MMC.

GrantX

Tue Sept 22 2015, 01:24PM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

nzoomed wrote ...

Does anyone know much about these russian ceramic caps on ebay?
There sees to be tons of old stock doorknob caps on ebay that were made in the USSR, but i dont know how reliable they are, but they also seem to be in rather low values, i need to make a 225nf bank for my MMC.

If I recall correctly, the ones marked "K15Ð£-1" are low loss RF ceramics, and seem to be very popular in VTTC's. I've got a few 10kV 2200pF and 8kV 3300pF examples laying around, but I haven't yet used them as tank capacitors. They seem abundant and cheap, but you'll need a huge pile to reach 225nF.

This site lists some of the common Russian capacitor codes, which makes searching ebay a lot easier:

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