[TCML] Looking for pulse cap
dave at leddon.net
Tue Sep 15 19:41:50 MDT 2009
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.
At 04:19 PM 9/15/2009, you wrote:
>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?
>----- 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
>>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.
>>At 01:36 PM 9/14/2009, you wrote:
>>>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?
>>>----- 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
>>>>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.
>>>>Tesla mailing list
>>>>Tesla at www.pupman.com
>>>Tesla mailing list
>>>Tesla at www.pupman.com
>>Tesla mailing list
>>Tesla at www.pupman.com
>Tesla mailing list
>Tesla at www.pupman.com
More information about the Tesla