Re: [TCML] Looking for pulse cap

[DC Cox <resonance@xxxxxxxxxxxx>]

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?
>> >> ?
>> >>
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