Re: Capacitor voltage - AC or DC

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Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>



One usually overrates the cap for AC use.  I suggest Erms x 2 as a 
correct DC rating, so with your 15 kV AC xmfr, for a near bullet 
proof cap bank, you want a cap bank rated at 30 kV DC.

If you are using 0.15 uF 2 kV caps in your strings then each 15 cap 
string would be rated .01 uF at 30 kV DC.

With a 30 mA xmfr you need approx .014 uF capacitance so you cheat a 
bit and use 11 caps in each string.  This gives you a single string 
rated .0136 uF at 22 kV DC which will work fine with your 30 mA 
xmfr.  You try to avoid a .01 uF match with the xmfr as the cap bank 
might resonate with the xmfr and damage the xmfr.  Going a bit higher 
usually works very well.   1.2-1.3 x Cres.

Dr. Resonance



Subject: Capacitor voltage - AC or DC


> Original poster: "Dirk Stubbs" <dirk@xxxxxxxxxxxxxx>
>
> Hello all
>
> I am building my first coil using a NST 15kv/30mA. With all the 
> research, I have been seeing people use these MMC capacitor arrays 
> but I have a question. Usually all these capacitors, that coilers 
> are using are DC rated but isn't there supply voltage AC? Does this 
> affect the capacitor?
>
> I know from my some of my other little projects involving DC(5-12V) 
> that reversing the polarity on a cap results in failure.
>
> Thanks,
>
> Dirk