Re: MMC Cap choice

["R.E.Burnett" <R.E.Burnett-at-xxxxxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Hi Steve and all,

These RS capacitors (RS 114-474) made by Arcotronics perform excellently
in Tesla Coil service.  Alan Sharp identified these for MMC use some time
ago,  and many UK coilers have used them in MMC arrays for a year or more.
They have been proven on coils from hundreds of watts up to around 10kva,
and throwing arcs up to 10 ft.

For anyone who is interested there is a more detailed data sheet available
here:
		http://www.arcotronics-dot-com/pdf/ec/a72.pdf

I think that the AC voltage rating with frequency is based on the 
temperature rise assuming a continuous current.  Our saving grace is that
the current is not continuous in the case of a TC tank capacitor.
Generally the capacitors have been run at the rated DC voltage with little
heating if enough strings are connected in parallel.

BTW. I think that the metal-foil/polypropylene capacitors are more
desirable for pulse capacitor use,  than the metalised polypropylene
alternatives.  The Aluminium foil is better suited to the high peak
currents.

There should be more information about this in the archives.

							Cheers,

							-Richie,

> Original poster: "Steve" <seric48-at-yahoo-dot-com> 
> 
> Neil, All,
> 
>   Those axial-leaded caps, according to the voltage/frequency graph
>  between the price list and the glowing description, are not rated
>  for Tesla coil frequencies.
> 
>   The AC rating (450VAC) stays the same through 10KHz, but drops
>  steadily from there to 90VAC at 100KHz. Not a good thing at all!
> 
> (Note to List: To see the cap data Neil's link referred to, go to
> 
>     http://rswww-dot-com
> 
>  select 'RS Stock No.' in the upper box of their search widget,
>  enter '114-474' in the lower box, and press the 'Go' button )
> 
>   Steve Copeland