[TCML] Looking for pulse cap

[Dave Leddon]

Herr Zapp,

If we figure a 90% voltage reversal at 100 pps and de-rating from 100 
kv to 10 kv we would should get 3.4 years of continuous use.  I don't 
know the effect of using a 1 pps cap at 100 pps but I think others 
have successfully done so by greatly de-rating the voltage.  Steve 
Ward raised another issue concerning the rms current rating of caps 
used in DRSSTC service.  He feels I should design for 200A RMS, at 
least in an MMC array, but I don't know if that would apply to a 
single large pulse cap.

Dave

At 04:19 PM 9/15/2009, you wrote:
>Dave -
>
>After a little searching, I found a 0.4uF, 100KV Maxwell in my 
>storage area. It's a model 31427, white single-ended plastic case, 
>about 4" X 6" X 29" tall. I bought this as a "used" part directly 
>from Maxwell in San Diego during a "garage sale" several years ago. 
>It's history is completely unknown, but I haven't done anything with 
>it since I bought it.
>
>Maxwell's datasheet shows a peak current rating of 25K amps, RMS 
>current of 25 amps, and an inductance of 20nH. However, rep rate is only 1Hz.
>
>The question is, what kind of a pulse rate "derating" could be 
>applied if it was only used at 10KV and 2500 amps?
>
>Regards,
>Herr Zapp
>----- Original Message ----- From: "Dave Leddon" <dave at leddon.net>
>To: "Tesla Coil Mailing List" <tesla at pupman.com>
>Sent: Monday, September 14, 2009 3:30 PM
>Subject: Re: [TCML] Looking for pulse cap
>
>
>>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 at leddon.net>
>>>To: "Tesla Coil Mailing List" <tesla at pupman.com>
>>>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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>>
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