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Finn Hammer

Fri Jul 15 2016, 11:28AM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

All,
I have noticed, that The typical mmc of The past, these days seems to be replaced by a single string of some rather beefy Looking capacitors.
I would appreciate a pointer to a source of these caps, since I have a medium sized coil in The planning stage.

Cheers, Finn Hanmer

Mads Barnkob

Fri Jul 15 2016, 11:47AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Ebay :)

There is always the chance of a good deal with make offer.

Generally any GTO snubber capacitor should be suitable,

Blackcurrant

Fri Jul 15 2016, 11:53AM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

You could try e-bay search for something like
doorknob high voltage ceramic

or they do sell them in RS or Farnell etc

use a filter to find the high voltage ones

profdc9

Fri Jul 15 2016, 01:11PM

Registered Member #58522 Joined: Tue Mar 15 2016, 08:33PM
Location:
Posts: 50

I think the Cornell-Dubliier 942C series is often used, in particular these:

Look for the self-healing polypropylene film types. The total voltage rating of the cap string is important, as well as the peak current, so if your peak current is high (300 to 400 A/pk) you may have to put several strings in parallel.

There are also cheaper Chinese capacitors you could try

For the higher values of capacitance you probably need several strings in parallel to reach the rated peak current.

I built a capacitor from sheets of aluminum roof flashing and polyethylene painters tarp, 26 nF @ 60 kVDC, using 23 plates separated by 3 mm of dielectric. It seems to work, but its rather bulky. No arcing through it the dielectric (yet).

Dan

Mads Barnkob

Fri Jul 15 2016, 01:51PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Finn is no new name in Tesla coiling business, he is not looking for the regular MMC capacitors you are suggesting, he is looking for large MKP snubber capacitors in the range of 1-2kV, 2-4uF, 50-100Arms, 1000Apeak.

Maybe you could even pioneer trying out those "DAWNCAP" on aliexpress ;)

Finn Hammer

Fri Jul 15 2016, 05:39PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

Thank you Mads, for hitting the nail on the head. Those Arcotronics caps look absolutely perfect, and almost cheap.

Also thank you to Blackcurrant and Profdc9 for trying.

Cheers, Finn Hammer

orac12

Sat Jul 16 2016, 08:37AM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

Has anyone used the acrotonics caps before and know if they are any good. Also any insight at to what the peak current rating may be?

Mads Barnkob

Sat Jul 16 2016, 08:52AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

orac12 wrote ...

Has anyone used the acrotonics caps before and know if they are any good. Also any insight at to what the peak current rating may be?

I got a lot of them, but have not used them yet.

I would estimate them to have very similar specifications as "same" rated on page 23-25:

Finn Hammer

Sat Jul 16 2016, 09:41AM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

orac12 wrote ...

Has anyone used the acrotonics caps before and know if they are any good. Also any insight at to what the peak current rating may be?

Orac12,

A datasheet usually shows up in PDF format, if you punch the manufacturers part number in Google:

I am among the pioneers of the Multi Mini Caps, since I was fortunate enough to join the Tesla Coil Community at the time, where Terry Fritz made the first one. I made the second one, and the rest is history.

From a gut feeling point of view, it would be nice to use capacitors with Solid metal electrodes, such as used in the much fabled DC942 series, where the external electrodes are made of foil. This ensures superior pulse current handling characteristics.
Due to a desire for self healing properties, the floating internal electrode is made from metallized foil.

I have found experimentally, though, that even high current primary tank circuits, such as the ones found in OLTC coils, and the Triggered BRISG coils, run well and reliably with capacitors constructed solely from metallized foil, for example the CD940.
It all boils down to building a capacitor that will sustain both RMS and Peak currents. The voltage ratings are quite a bit more funky.
The mentioned Arcotronics caps have a peak current rating of 1600A, and that should suffice for a single string, even up into the larger coils, over time, the voltage rating has shown to be DC rating = AC rating in a tesla coil.

So I intend to use them in my next coil, 10 in series, for 500nF in a 2XSemikron SKM400GB124D based coil.
Like Terry told me, about 16 years ago: "I wouldnÂ´t worry much, Finn, Just build it, and It will work fine"

I have just placed an order for 25 of the arcotronics caps, I will put them into a coil designed to take the steam out of one of the last no-goÂ´s of Tesla coiling, so we will soon know.

Cheers, Finn Hammer

orac12

Mon Jul 18 2016, 07:35AM

Registered Member #9879 Joined: Tue Jan 29 2013, 05:00AM
Location: New Zealand
Posts: 37

Thanks, I did search the part number but found nothing. They seem they will be suitable for my coil and future projects, have ordered a few..

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