Re: [TCML] Capacitor differences

[Steve Ward <steve.ward@xxxxxxxxx>]

Your peak current calculation looks right (545A), but the RMS in this case
is not just simply the Ipk * 0.707 (that only works for continuous signals),
its actually much harder to derive because it depends on break rate and the
time it takes for the primary current to ring down.

If i had to guess, the RMS current in your situation would probably not
exceed the capacitor rating to a degree that is dangerous for short runs,
but in general it will be 10's of amps for a coil like yours.

Also, maybe you grabbed the wrong Ipk values from the datasheets, i see 432
and 216A for the 942 and 940 respectively.  The proposed 940C bank thus has
an Ipk rating of 648A, and Irms of 30.3A, which sounds like a pretty safe
margin to me.

Steve


On Fri, Apr 23, 2010 at 10:43 AM, Miles Mauldin <teslamiles@xxxxxxx> wrote:

> Hi Steve,
>
> My plan was to use 3 strings of 15 each of the 940C30P15K-F to get to 30nF,
> at 45kV.  I am using 3 NSTs of 12kV/30mA each in parallel (90mA).  If I have
> done my math correctly I come up with 545A peak, 385A rms using 29uH for L,
> 30nF for C and 16970V for Vpk.
>
> 3 Strings of 15 each 940C would be 177A pk and 8.1A rms
> 3 Strings of 15 each 942C would be 231A pk and 8.4A rms
>
> Looks to me like I would be stressing the 942C series as well.  Or is this
> ok for short (a minute or two) runs?
>
> http://www.cde.com/catalogs/942C.pdf
> http://www.cde.com/catalogs/940C.pdf
>
>
>
>
> ________________________________
> From: Steve Ward <steve.ward@xxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Fri, April 23, 2010 10:24:58 AM
> Subject: Re: [TCML] Capacitor differences
>
> I think the problem is that very few coilers actually figure out how to
> spec
> their capacitors, and stay within the component ratings for peak current.
> I
> too use the 940C series on my solid state systems, but im careful to mind
> the specs that the manufacturer gives!  Yes, the 942C series handles more
> peak current, the datasheet says it, nothing to figure out there!  Dont be
> surprised when your caps break because you exceeded the current rating.
>
> Ipk = Vpk / SQRT(L/C)
>
> Is that so hard?
>
> Steve
>
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