Re: [TCML] Looking for pulse cap

[Steve Ward <steve.ward@xxxxxxxxx>]

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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