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Re: rolled caps


From: 	Mad Coiler[SMTP:tesla_coiler-at-hotmail-dot-com]
Sent: 	Saturday, September 06, 1997 3:22 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: rolled caps

>From: 	Geoffrey Schecht[SMTP:geoffs-at-onr-dot-com]
>Sent: 	Saturday, September 06, 1997 9:46 AM
>To: 	Tesla List
>Subject: 	Re: rolled caps
>
>Answers to questions:
>
>1.) Having a PE-al-PE-al cap will give you about about half of the
>capacitance of a PE-al-PE-PE-al cap since capacitance is directly 
inversely
>to plate separation

I think you meant double the capacitance.

>(I think that I understood the question...maybe you
>should repost with a layer scheme like the one I just used).
>

I dont think you eactly understood. The actual distance between plates 
should stay approximately the same - three thicknesses of 30 mill PE. I 
will attempt to show the two chioces I am facing:
--     plate A
O    PE 1
O    PE 2
O    PE 3
--    plate B

OR

--     plate A
O    PE 1
--     AL (spacer)
O    PE 2
--     AL
O    PE 3
--    plate B

Since the AL inbetween the PE layers is electricaly shorted from one 
side to another it shouldn't add to the total seperation of the plates. 
Another way to see this is that as the thickness or the dielectric 
increases the capacitance goes down. In both models the thicknes of the 
dielectric is constent - 90 mills. I just thought that having conductive 
plates between might improve the efficiency of energy storage. Having 
the extra plates would allow smaller charges to act on each other at 
closer distances, perhaps allowing it to be better at pulse type 
discharging? Hmmm, is that any clearer?

>2.) LDPE can be contaminated by any fatty acid such as you find in 
soap.
>One of the cleanest solvents that you can buy is, believe it or not,
>Everclear 190 proof grain alcohol. We used to use it to clean nuclear
>detector circuits which couldn't tolerate leakages even in the low nA
>range. It was one of the only things that would properly decontaminate
>teflon standoffs after normal flux removers were used (plus it was 
great
>fun to have around after-hours). Having dust buried in the 
dielectric-al
>interface probably doesn't hurt anything; I'd think that leakage over 
and
>around the dielectric area is what could invite a flashover betwen 
plates,
>assuming all other things are properly spaced. 
>
>3.) Polyethylene has a breakdown strength of 1200V/mil at 60 Hz and 25 
deg.
>C. Theoretically, you should be good for 48kV but I think that I'd 
derate
>that by 50% since you probably don't have critically-controlled 
thickness
>in your poly sheeting and it could have thin spots or possibly some 
voids.
>Sounds like you're pretty safe at 15kV but I'd give it a once-over 
under
>polarized light to check for thin areas (that might work, it'll at 
least
>find stress areas).
>
>I'd recommend wearing clean latex or nitrile gloves after you clean the 
PE
>to avoid recontamination from skin oils and only work on clean,
>decontaminated surfaces until the cap is rolled up and secured/sealed.
>
>Good luck.
>
>Geoff
>
>
>> 
>> 
>> From: 	Mad Coiler[SMTP:tesla_coiler-at-hotmail-dot-com]
>> Sent: 	Friday, September 05, 1997 4:16 PM
>> To: 	tesla-at-pupman-dot-com
>> Subject: 	rolled caps
>> 
>> To all that have made rolled caps,
>> 
>> I have just recieved my order of 30 mill LDPE sheets. I plan on 
making 
>> the dielectric three sheets thick. This would be 90 mills, and I 
hopped 
>> this would be enough for 12000V.
>>  Question (1): Should you put aluminum flashing between each sheet of 
>> the dielectric or just set three sheets together without anything 
>> inbetween.
>>  Question (2): I assume the plastic should be clean. Is LDPE 
sensitive 
>> to soap, or should a damp cloth work fine to get the dust off?
>>  Question (3): Will three layers of 30 mill also work for 15kV or do 
i 
>> need more?
>> 
>> Mad Coiler
>>