RE: [TCML] My terry filter capacitors blew up!!

["Lau, Gary" <Gary.Lau@xxxxxx>]

There's a couple of problems here.

First off, if the value of your tank cap is exactly resonant with your NST, that's a bad thing.  It should be Larger Than Resonant (LTR) to prevent mains-resonance from destroying things.  For a 15/30 NST at 60Hz and a static gap, a 0.01uF cap would be a good choice.

For your Terry filter, did that include the MOV's and safety gap?  The MOV's should have clamped any excessive voltages, possibly smoking them in the process.  Similarly, a properly adjusted safety gap should do likewise, though the key word here is "properly".  Opening it up to where it doesn't arc renders it useless.

The total capacitance on each side of a Terry filter should be in the ballpark of 500pF.  If you try to make a 500pF cap out of .015uF units, you'd need 30 - kind of a waste.  If you use fewer caps, you end up with a higher capacitance, which wastes a lot of power.

If you smoked a string of 12 1.6kV caps, that means the NST hot terminal to ground was over 19.2kV, or over 38kV terminal-to-terminal!

I would suggest:
1) Make sure your main static gap width is properly set.  Opening the gap too wide causes the voltage to climb to very destructive levels, especially when your main capacitor is mains-resonant with the NST.
2) Same thing with the Terry filter safety gaps.
3) If you can, try to increase the main cap size so as to not be mains-resonant.
4) For the Terry filter caps, you may want to consider using doorknob caps from ebay, typically 500pF/30kV.  They're not too costly and smaller than building an MMC.

My Terry filter and a lot of explanatory text may be seen at http://www.laushaus.com/tesla/protection.htm

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Ln2guy42@xxxxxxx
> Sent: Tuesday, February 05, 2008 11:38 PM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] My terry filter capacitors blew up!!
>
> Hello all,
>
> Recently I built an MMC for my medium sized 4.5 inch diameter Tesla coil,
> and the total value for it is .0053uf at around 35,000 volts. This is resonant
> for my Magnetek 15kv 30ma NST.
>
> I had a Terry filter on the NST, (i bought the kit off ebay) and when  I ran
> the coil, the capacitors on the Terry filter blew up and caught fire. I  was
> wondering why this is, and also I need to know how I can replace the  caps.
>
> Do they need to be the exact same kind of capacitors? The  ones that blew
> were .0033uf at 1600v each. There were 12 capacitors in series.
>
> I was wondering if I could use these other caps I had which are  0.015uf each
> at 1600v. I have around 20 of those.
>
> Would the extra capacitance make a difference? How does the capacitance
> affect the Filter and in general the whole Tesla Coil?
>
> Sorry if I seem naive to this, but I'm only 14 years old.
>
> I really appreciate this a lot!!!!
>
> Thanks,
> Amir M.
>
>
>
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