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Re: Need Help With Capacitor

Hi richard.

In response to your doubts about constructing yout cap.
I have been where you are.
Knowing that my cash flow was slow, I decided to try my hand at building a
cap for my coil.
What resulted from my trial is as follows.
For my 1st try, I cut 10 5 inch discs from aluminum foil that had 1 inch
wide by 4 inch long tabs coming out on one side. Then I cut 10 6 inch .010
mylar film disks. On a 1 inch thick by 2 foot by 2 foot teflon work surface,
I made a 'sandwitch' of mylar, foil 'tab on left', mylar, foil 'tab on
right', ect. ect. you get the picture. I next placed a 6 inch by 6 inch
block of teflon on top of this sandwitch to compress this mess. I put my
test coil on top of this thing and made my conections to this cap thing with
aligator clips to each group of foil tabs. I fired it up, spark gap set to
about 5kv, and tried to tune the primary circuit. Just as the circuit was
comming into resonance, snap crackle pop!! break down!
OK no problem I think, i'll just double the mylar film and number of
aluminum foil disks.
Fire up the thing again,,,, snap crackle pop!!!! damn ! 
OK well,ll,ll  I'll put triple layers of mylar .030 total ya thats it!
well guess what? still Breaks down. Humm, ?? I cannot see any holes in the
mylar, whats going on?
Suddenly I have sort of sick idea! I run upstairs to my wifes kitchen and
spot a tupper ware bowl with a lid on it, it's about 8 inches in diamater. I
grab it and head down stairs. Next I spot a new bottle of 10w40 motor oil.
Oh what a mess this will be!!
I put this cap 'thing' in the tupperware bowl and add the motor oil to it. I
squeezed out all of the air I could.
Ok, now I put my test coil on and fire it up! wow! no break down!! seems to
work ok. I add more aluminum plates to my cap for more capacitance. Value of
my cap is .014uf. I am runing about 10kv or so from a neon sign x-former.
The cap is 2 .010 inch mylar disks between the foil plates. Total height of
stack is about 5/8 inches. With test coil running at max, about 12 inch
streamers, I can just see a slight blue glow through the clear top of the
tupperware container. The cap gets slightly warm after about 15 minets of
opperation. The opperation of the test coil is at its best with this cap!!.
I have used a stack of doorknob caps in parallel, they just don't work as
well. Also this cap 'thing' has an air tight lid on it and is not vented. I
have never noted any pressure buildup in it! I would not say you do not have
to vent this kind of cap, I just haven't the heart to cut a vent hole in my
wifes bowl.
I have disassembled this cap after about 10 hours of continous opperation. I
have noted a slight discoloration on the mylar film located at the very
edges of the foil.
I suspect that this goes with the slight blue glow at max voltage settings
on my coil. I belive that this is some type of corona discharge.
Richard, I hope this will give you some examples of what you can do with
home made caps!
If any one has comments on this, lets hear it!!!

                          bye for now,  Matt B.
                                        mattjb-at-rmii-dot-com


 At 02:35 PM 2/4/96 +0700, you wrote:
>>From richard.quick-at-slug-dot-org Sat Feb  3 14:12 MST 1996
>>Received: from uustar.starnet-dot-net (root-at-uustar.starnet-dot-net
[199.217.253.12]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with SMTP id NAA26566
for <tesla-at-grendel.objinc-dot-com>; Sat, 3 Feb 1996 13:58:28 -0700
>From: richard.quick-at-slug-dot-org (Richard Quick)
>Subject: Need Help With Capacitor
>Date: Sat,  3 Feb 1996 19:34:00 GMT
>To: tesla-at-grendel.objinc-dot-com
>
> * Original msg to: Oldradio-at-cheney-dot-net
> * Carbons sent to: usa-tesla-at-usa-dot-net
>
>Quoting "James M. Watson" <oldradio-at-cheney-dot-net>:
>
>> Hello Richard.
>
>> I am about to begin constructing my first capacitor, and 
>> another bit of doubt has popped up.  I will be constructing a 
>> flat stacked plate capacitor, with the plates being discs made
>> from aluminum flashing; the housing will consist of 10"OD PVC 
>> sewer pipe (previsions for pressure build up will be made). 
>
>This sounds OK. You won't have much of a problem with pressure
>rise, and as I mentioned there is no need to prepare the PVC pipe
>container. Just make sure it does not leak... Will you turn it on
>it's side when it is done, or pull the air out of the stack with
>a vacuum pump?
>
>> The dielectric will be three layers of .030 polyethylene.  Each
>> plate will have a small tab which I will attach to either an 
>> aluminum or copper bus bar.  The closest point between any two
>> opposing plates will be where this tab comes out of the 
>> dielectric.  Do you think that 1" separation at this point 
>> would be enough to prevent fringing, considering that I will be
>> using mineral oil, and the input will be 15kV? 
>
>This sounds like it will work fine. If you are worried about
>flashover beneath the oil you can mount an extra safety gap
>across the capacitor terminals. The safety gap can be set for the
>same width as the closest points between your conductors under
>the oil. Given that the dielectric strength of oil is
>considerably higher than air, the air gap across the capacitor
>terminals will fire before the oil dielectric breaks down.
>
>> Would an aluminum bus bar serve well (1/4" thick x 3/4" = 
>> wide)?   Is there any problem with using PVC sewer pipe for the
>> housing? 
>
>The bussing sounds heavy enough, depending of course on the value
>of the capacitor and peak current the bussing is required to
>handle. At these frequencies the bussing does not need to be so
>thick as is does wide. Your charging amperage will be measured in
>miliamps at 50/60 AC, which any reasonable conductor will handle
>without worry. Your pulse discharge is going to oscillate
>however: a smooth wide strap will have the lowest resistance to
>this type of energy.
>
>As I mentioned, the only care you need to take with the container
>is to make sure it won't leak... If you intend to pump the cap
>down to remove air it must withstand the vacuum.
>
>Richard Quick
>
>
>... If all else fails... Throw another megavolt across it!
>___ Blue Wave/QWK v2.12
>
>
>