Re: [TCML] Looking for pulse cap

[Dave Leddon <dave@xxxxxxxxxx>]

Herr Zapp,

I've been discussing igbt current limits with Steve Ward who felt 
that 2400 Amps should be the upper limit for my CM600 bridge.  The 
operating frequency of my coil is 37 khz with a tank capacitance of 
0.5 mfd.  At that frequency the impedance of the cap is 8.6 ohms and 
so at 2400 amps that works out to 20647 volts.  My present MMC array 
consists of three strings of 12 each 942C8W2K-F capacitors 2 mfd at 
850 vdc, 360 vac which limits me to something less than 1000 
amps.  Steve suggests using the peak value of the ac rating to insure 
longevity, which in this case would be 509 volts.  Using this 
conservative peak rms voltage rating I would require 11 strings of 41 
each of the 942C8W2K-F caps for a total of 451 and at about $5 each 
that works out to $2255. I could save a little bit my using the 
940C8W2K-F which has a 450 v rms rating and slightly lower cost but 
the bottom line is that the single surplus pulse cap is bound to be 
the better deal.

Regards,
Dave



At 01:36 PM 9/14/2009, you wrote:
> Dave -
>
> A few questions:
>
> 1. How are you calculating the voltage requirements for the tank cap?
>
> 2. How large a multiplier are you using to define the capacitor's 
> voltage margin (safety factor)?
>
> 3. What is the manufacturer's voltage rating for the IGBTs you will be using?
>
> 4. What is the calculated peak primary current?
>
> Regards,
> Herr Zapp
> ----- Original Message ----- From: "Dave Leddon" <dave@xxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Monday, September 14, 2009 11:19 AM
> Subject: [TCML] Looking for pulse cap
>
>
> > Hi all,
> >
> > I'm working on a fairly large DRSSTC and I find that an MMC 
> > adequate to the task may be out of my financial reach.  If I were 
> > to push the igbt bridge to its limits I would require a cap rated 
> > at 20 kv at 0.5 mfd. This begins to sound like pole pig 
> > territory.  If anyone has a cap like this that they would consider 
> > selling, or if they know of a resource that I can pursue, please let me know.
> >
> > Thanks,
> > Dave
> > Pleasanton, Ca
> >
> > _______________________________________________
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> > Tesla@xxxxxxxxxxxxxx
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>
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