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Re: [TCML] MMC help
Hi James,
Hobbyists typically construct their MMC's with the string voltage rating
greater than or equal to the peak NST voltage. So for your 15kV NST, that
would be about 21kV, so you have plenty of headroom.
Also typically, we try to size the capacitance to ~1.5X the mains resonant
value, which for your 15/60 NST, is about .01uF at 60 Hz (about .013uF @50
Hz). This is known as an LTR or Larger Than Resonant value, and has been
found to perform better and have lower risk of damaging the NST should your
spark gap be set too wide. So if you're in 60 Hz land, I would recommend
targeting ~.015uF, but the exact value isn't at all critical.
So you could use a lower number of caps per string, which would reduce the
voltage rating while increasing the uF rating.
I don't think there's any functional problem with the cap you've selected,
but you may find you bet more bang for the buck (or pound or euro) if you
select a cap with a higher uF value, to avoid having to assemble soooo many
caps as you're looking at!
Regards, Gary Lau
MA, USA
On Mon, Apr 25, 2011 at 8:04 PM, James Hutton
<b-u-r-t-o-n-boy@xxxxxxxxxxx>wrote:
>
> hello, I was wondering if someone can help me.I had ordered 276 of these
> capacitors:
> http://uk.farnell.com/jsp/search/productdetail.jsp?CMP=i-ddd7-00001003&sku=9751602<http://uk.farnell.com/jsp/search/productdetail.jsp?CMP=i-ddd7-00001003&sku=9751602in>hopes of having a series parallel circuit of 23 parallel strings, with 12
> caps per string. This would give me 30,000v @ 0.0107uf (i need
> ~0.0106uf)so, very conveniently, they decided to round and ship 275 of
> these! (i know, my fault for not adding some spares)so now i am left with
> the option of putting 21 parallel strings, with 11 caps per string (giving
> me 27,500v @ 0.0106uf)
> or
> 22 parallel strings with 12 caps per string (giving me 30,000v @ 0.0102 uf)
> *my transformer is a NST 15,000v @ 60ma
> -basically what im asking is will it be risky having only 27,500v but the
> right capacitance, or will the capacitance not matter that much if it is
> close enough to 0.0106uf
> thank you for any help!
> -james
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