[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] Looking for pulse cap

DC,

Can you clarify?  What stray inductance?  If you mean in the cap bank, then
no, it will not kill the IGBTs.  Stray inductance in the primary circuit
will only reduce coupling to the secondary.  It will NOT kill the IGBTs.

Zapp,

The 25A RMS on that capacitor you speak of is really worrying.  I'd expect
Dave's tank circuit to have a RMS current of several hundred amps.

-Phillip Slawinski

On Tue, Sep 15, 2009 at 19:11, DC Cox <resonance@xxxxxxxxxxxx> wrote:

> With a classic RSG coil, no problem.
>
> With an IGBT coil the sum of all the stray inductances would kill the
> IGBTs.
>
> Dr. Resonance
>
>
>
>
> On Tue, Sep 15, 2009 at 1:25 PM, Dave Leddon <dave@xxxxxxxxxx> wrote:
>
> > Phillip, Steve,
> >
> > Thanks for your insight.  You both responded almost simultaneously with
> the
> > suggestion that I raise the value of my tank cap to 1 uf which has
> several
> > advantages, not the least of which is that it reduces the capacitor count
> > down to something almost manageable.  Using the 940C8W2K-F caps ($5.99 at
> > rell.com) I could get by with 9 strings of 17 each and given that I
> > already have 38 of these on hand my out of pocket expense would only be,
> > ka-ching $690.  Still a bit more than I can justify.  So if anybody knows
> > where I can score 1 uf at around 10,000 volts for less money, please let
> me
> > know.
> >
> > Thanks,
> > Dave
> > Pleasanton, ca
> >
> > At 11:20 AM 9/15/2009, you wrote:
> >
> >> Herr Zapp,
> >>
> >> The lower voltage ratings you may have seen were for 2 reasons: less
> >> current
> >> and secondly, they were over stressed.
> >>
> >> I used to run my MMC caps with peak AC voltages at the DC rating, and
> >> after
> >> enough time, one by one, the caps would fail.  Testing shows that the
> cap
> >> makers arent fibbing about the VAC ratings, stick with that and it will
> >> last
> >> for a really long time.
> >>
> >> Dave,
> >>
> >> Id suggest going up higher than .5uF, perhaps to 1uF or so (i didnt
> >> specify
> >> this in our correspondence).  Im running 1.25uF on an experimental setup
> >> at
> >> 1500A, but a lower frequency.  While you get less amp-turns in the
> >> primary,
> >> you do arrive at the higher peak current level faster, which translates
> to
> >> achieving a certain top voltage on the toroid faster, which is more
> >> efficient (in my data i saw a 20% efficiency improvement going from 8
> >> cycles
> >> to 5 cycles of operation by increasing the tank cap value).  You have
> >> current to spare with those big CM600s, so you should have no problem
> >> producing well over 10 foot sparks (id guess in the 14-16 foot range,
> >> secondary coil withstanding).
> >>
> >> Steve
> >>
> >> On Tue, Sep 15, 2009 at 10:48 AM, Quarkster <quarkster@xxxxxxx> wrote:
> >>
> >> > Matt -
> >> >
> >> > Eh??
> >> >
> >> > Clearly, my post contained no answers whatsoever, only questions to
> try
> >> to
> >> > gain a better understanding of Dave's rather unique capacitor
> >> requirements.
> >> >
> >> > Most of the large DRSSTCs that I've seen get by using a cap with a
> lower
> >> > voltage rating, but they may not actually be attaining a primary
> current
> >> of
> >> > 2400A.
> >> >
> >> > Regards,
> >> > Herr Zapp
> >> > ----- Original Message ----- From: <mddeming@xxxxxxx>
> >> > To: <tesla@xxxxxxxxxx>
> >> > Sent: Monday, September 14, 2009 5:37 PM
> >> >
> >> > Subject: Re: [TCML] Looking for pulse cap
> >> >
> >> >
> >> >
> >> >> Hi Herr Zapp,
> >> >>
> >> >>
> >> >>
> >> >> Interesting questions, but how do they relate to answering the
> question
> >> >> Dave asked?
> >> >>
> >> >> Matt D.
> >> >>
> >> >>
> >> >>
> >> >> -----Original Message-----
> >> >> From: Quarkster <quarkster@xxxxxxx>
> >> >> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> >> >> Sent: Mon, Sep 14, 2009 4:36 pm
> >> >> Subject: Re: [TCML] Looking for pulse cap
> >> >>
> >> >>
> >> >>
> >> >> 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?
> >> >> ?
> >> >>
> >> >>> _______________________________________________?
> >> >>> Tesla mailing list?
> >> >>> Tesla@xxxxxxxxxxxxxx?
> >> >>> http://www.pupman.com/mailman/listinfo/tesla ?
> >> >>>
> >> >> _______________________________________________?
> >> >> Tesla mailing list?
> >> >> Tesla@xxxxxxxxxxxxxx?
> >> >> http://www.pupman.com/mailman/listinfo/tesla?
> >> >>
> >> >> _______________________________________________
> >> >> Tesla mailing list
> >> >> Tesla@xxxxxxxxxxxxxx
> >> >> http://www.pupman.com/mailman/listinfo/tesla
> >> >>
> >> >
> >> > _______________________________________________
> >> >
> >> > Tesla mailing list
> >> > Tesla@xxxxxxxxxxxxxx
> >> > http://www.pupman.com/mailman/listinfo/tesla
> >> >
> >> _______________________________________________
> >> Tesla mailing list
> >> Tesla@xxxxxxxxxxxxxx
> >> http://www.pupman.com/mailman/listinfo/tesla
> >>
> >
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla