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Re: [TCML] My last question on caps. I swear. (maybe)
> From: Nicholas J. Goble <ngoble@xxxxxxx>
> Subject: [TCML] My last question on caps. I swear. (maybe)
> 942C20P15K-F caps. They're rated at 2000VDC and .15uF.
> If I string
> them together in series, I'll get an MMC at 24000 Volts
> and .0125uF.
> Two things worry me.
>
> 1). The website says that it's rated for 2000VDC.
> I'm not using
> direct current. There's a link to a data sheet for the
> caps and it
> says that the voltage range is 600-2000 VDC or 300-500 VAC.
> If I
> series 12 of these together, will I get an MMC rated at
> 24000 VDC and
> only 6000VAC? Does this mean that I've got to string
> 48 caps to get an
> MMC that will work at 24000VAC? Or will 12 2000VDC caps
> work just fine?
Yes, that last thing you said. 2000vdc per cap x 12 = 24000vdc peak rating. Such a cap can handle your 9kv NST with both hands tied behind its back. Commercial polypropylene snubber caps in general and CD942 caps in particular seem to be very conservatively rated. The manufacturers deliberately low-ball the amount of voltage they can handle. Coilers can get away with using the DC rating--usually. Some coilers have exceeded even the DC max rating by a significant margin and still gotten away with it.
>
> 2). The website shows a picture of the caps. On the side
> of the caps,
> it says it's rated .15MFD. Why would it say that? I
MFD is an old-school way of expressing MicroFarad. So .15MFD = .15uF. I know how you feel. As an instructor of basic electronics, stuff like this simply spreads confusion. One student of mine who saw this "MFD" expression in a parts catalog became convinced it meant MegaFarad. Based on the T-G-M-k-(units)-m-u-n-p standard units chart, who's to say he is wrong? Big M means "Mega", right? Wrong. In this case, it means "micro".
> thought
> 942C20P15K-F caps were rated at .15uF. This isn't a
> huge concern of
> mine, but it's making me worry about my purchase.
Don't worry--all is well.
> Thanks for putting up with me.
>
> Nicholas Goble
Cheers,
Greg
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