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Re: Cornell-Dubilier caps (was salt water caps or buckets?)
Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
Hi Chris and Garry,
CD makes all kinds of caps. The ones Garry used (940C20S33K) definitely
got real hot fast but some ran cool too. I think they have a very low
dV/dT rating and the end connections failed (they may have been ALL
metalized). I imagine CD got you the best high current caps for your
project. Do you know the exact part number? Some people have had great
luck with CD caps so I imagine it is a matter of getting high vs. low dV/dT
parts. All manufacture's use the same "stuff" so I bet it is simply a part
number/application issue. I think I see (942C) on your caps which are
probably very high current types since I remember that number...
http://www.cornell-dubilier-dot-com/
"Style 940C, Round, axial film capacitors use polypropylene film and dual
metallized electrodes for both self healing properties and high peak
current carrying capability (dV/dt).
This series features low ESR characteristics, excellent high frequency and
high voltage capabilities."
"Style 942C, Round, axial film capacitors utilize a hybrid section design
of polypropylene film, metal foils and metallized polypropylene dielectric
to achieve high peak current ratings.
This series is ideal for high pulse operation and high peak current circuits."
The 940C looks like they just have metal film electrodes and the 942C has
solid metal foil electrodes. They both list pretty high dV/dT but the
metalized electrodes do not make solid connections to the end caps which is
what cooked Garry's caps.
http://hot-streamer-dot-com/TeslaCoils/Misc/blownMMC/
http://hot-streamer-dot-com/TeslaCoils/Misc/blownMMC/Pc020019.jpg
Yep, this last picture shows where I ripped one apart and the layers are
metal film, not foil. The dV/dT may "seem" high for a single pulse
(probably what CD tested) but wee need them to hit 120BPS all day long ;-))
There is a big difference between single shot and 120BPS... Also note how
poorly the few millionths inch thick film layer attached to the end caps
which was the real problem here...
Cheers,
Terry
At 03:49 PM 4/3/2001 +0000, you wrote:
>>Original poster: "Bill Vanyo by way of Terry Fritz <twftesla-at-uswest-dot-net>"
>><vanyo-at-echoes-dot-net>
>>
>>Tesla list wrote:
>> >
>> > Original poster: "Christopher Boden by way of Terry Fritz
>><twftesla-at-uswest-dot-net>" <chrisboden-at-hotmail-dot-com>
>> > Complete plans for a bucket cap can be found at...
>> >
>> > http://www.thegeekgroup-dot-org/Projects/Tesla/capacitors.htm
>>
>>I noticed you're using Cornell-Dubilier caps. I have a bunch of these
>>(.047uF 3000vdc) that I was planning on using for an MMC. Then I found
>>a doc on one of Terry's pages (which I can't find now - it listed
>>"good" caps and "bad" caps for MMC's), and the Cornell-Dubilier's were
>>the only "bad" cap listed. I know somebody else on the list used these
>>and they blew rather easily. Are they working for you? Maybe the ones
>>you have are constructed differently - mine are pure metallized film, no
>>foil (I unrolled one).
>
>I believe Robin Coprini is using the same ones as we are, and he's got a Pig
>system on his.
>
>Ours came directly from CD (not a distributor) as part of their sponsorship
>of the Group. We've pounded the caps several times and never had a failure.
>They've been run below freezing, and moved dozens of times.
>
>Maybe our MMC is different. I've never seen one built like ours (and having
>spent 4 days drilling holes I know why) most of them are VERY different.
>I didn't read Terry's chart (good thing too) and we didn't pick CD, they
>picked us. We begged every cap producer out there. CD was the first to
>accept us for sponsorship. It took us almost a year to get a cap sponsor,
>and it has definately been worth it. After we got the company, Mark Broker
>speced the caps and designed the MMC electrically.
>We spent a month scrounging materials (Lexan, resistors, etc) then we all
>got together here at Little St to build them. On the first day we decided (I
>have no idea why) to radically change the design (we were gonna use the
>Coprini design) to the one you see on our site.
>
>I designed the layout of having the caps held in place by their leads and
>floating in open air, the resistors too. I mentioned it while we were
>screwing around with the lexan and we all thought it would greatly help
>cooling, completly elimate arcover, and look radically different than
>anything else out there. The downside is they took FOREVER to build and were
>WAY more labour intensive than they had to be. We wasted a lot of time
>stuffing caps into little holes only to have them all fall out as you tried
>to get the top piece on....ugh.
>
>We have the Pig system coming together now as we get settled into Sigma-6
>and will be testing the caps to their design limits and beyond. I'll let you
>know what happens. So far we have CD caps in 3 of our large cap
>applications. We have the 4 MMC banks without a failire (thank God, it'll be
>impossible to replace an individual cap without a LOT of work). We have a
>room full of electrolytics (250 caps, each 450VDC -at- 1500uF) for our Project
>Thumper. And we have 100 of the 25kV mica caps for the Groucho Project (Marx
>bank). I hope they all survive :)
>
>
>
>>
>>BTW, your page (listed above) doesn't view under Netscape 4.7
>>
>
>lol....that's been an ongoing struggle for 2 years now. We made our site in
>Frontpage and the CSS files are screwy. We are currently in the process of
>recoding the entire site in Dreamweaver and Flash. Within 2 months (we have
>a REALLY big site) it will be done and replace the code-nightmare that is
>our current site.
>
>
>> - Bill
>
>Are you a member yet?
>
>Have fun!
>
>Christopher A. Boden Geek#1
>President / C.E.O. / Alpha Geek
>The Geek Group
>www.thegeekgroup-dot-org
>Because the Geek shall inherit the Earth!
>
>
>
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