Re: MMC Substitute
Mads Barnkob, Fri Jul 15 2016, 11:47AM

Ebay :)

or

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

Generally any GTO snubber capacitor should be suitable,

Re: MMC Substitute
Blackcurrant, Fri Jul 15 2016, 11:53AM

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

Re: MMC Substitute
profdc9, Fri Jul 15 2016, 01:11PM

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

Re: MMC Substitute
Mads Barnkob, Fri Jul 15 2016, 01:51PM

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 ;)

Re: MMC Substitute
Finn Hammer, Fri Jul 15 2016, 05:39PM

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

Re: MMC Substitute
orac12, Sat Jul 16 2016, 08:37AM

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?

Re: MMC Substitute
Mads Barnkob, Sat Jul 16 2016, 08:52AM


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:

Re: MMC Substitute
Finn Hammer, Sat Jul 16 2016, 09:41AM


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 wouldn´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-go´s of Tesla coiling, so we will soon know.

Cheers, Finn Hammer

Re: MMC Substitute
orac12, Mon Jul 18 2016, 07:35AM

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..

Re: MMC Substitute
nzoomed, Mon Jul 18 2016, 09:16AM

There are lots of cheap chinese MKP caps on ebay that are worth while experimenting with and testing for tesla coil use.

If they prove durable, they very well may be a good option, but i dont know what the ESR would be like on them.

Re: MMC Substitute
Hydron, Mon Jul 18 2016, 09:08PM

Another option that's a little smaller than the beefy GTO caps is running a string or two of the IGBT direct mount snubber caps in series. I have successfully used two strings of the 2uF/1kV Aerovox snubbers (see ). Can be picked up as used surplus very cheaply (I paid $100 USD for 50, shipping to NZ cost more than the caps!)

Re: MMC Substitute
Justin, Tue Jul 19 2016, 07:13PM

I just bought some of these, you or someone else might find them suitable.

NOTE: These are all glued using silicone adhesive, a real pain in the ass to remove.