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My first MMC cap test.

Original poster: Tesla <tesla@xxxxxxxxx>

Hi all.

I am designing three new coils at the time. A couple of days ago i tested my medium tabletop
with my first MMC. Never used this type before but everyone seems to get good results so i gave
it a try.

The tank cap MMC consists of nine 0,150uF/1200VDC caps for a total of 16,6nF/10800VDC.

The transformers used are two NST's(4kV/45mA) connected in serial for a total of 8kV/45mA.
Now i know that i probably should have used a much higher DC rating for this setup but some
people have gotten good results with using a bit higher DC rating than the transformer can deliver(in AC).
So i figured i would test with this setup.

I started by shorting out three of my gaps to charge the capacitor with a voltage of about 2000VAC just
to see if it worked as it should. I turned up the variac to about 50 Volts and the gap gave that typical
sparc of a functioning system. Voltage across the capacitor was about 1700 VAC.
It seemed to work so i only shorted two gaps for the next test. This would give a charge of approx
4kV. I turned the variac up to about 90 Volts and the gap were firing as it should. Input to the tank
was approx 3100 VAC when after about four seconds it just stopped.

I surmised that something had gone wrong so i disconnected everything and checked all components.
Everything seemed fine so i tested again. I turned the variac up to 50 Volts and heard a sort of buzzing
sound. At first i thought this was due to near-breakut at the sparkgap but when i inspected it closer it
turned out to be the MMC.

Now i wasn't sure that these caps would do the trick. Obviously they didn't. But i'm surprised that they
didn't even managed 3100 VAC for a longer period than a few seconds. I guess these capacitors can
be safely added to the BAD MMC list.

The cap type : MKP
Manufacturer : SCR
Capacitance : 0,150uF
Voltage : 1200VDC/600VAC

Question is has anyone else tried these caps for a MMC cap?

I have ordered a new batch of Evox Rifa, type PHE 450 (Metallized polyprop cap). Yes i know these
aren't the best types and that i should find foil caps. Unfortunately i can't find any from a supplier
here in Sweden.
They new ones have the same capacitance but a DC rating of 2000V and an AC rating of 700V.
I'm still a bit low on the Voltage rating but i will try these to see if i get a better result. Nine of them
isn't expensive to test with anyway.


Matthias "Tesla" Andersson
-"Why Am I Glowing In The Dark?"

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