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My extended-foil cap failed.... To Gary: my cap died, too.
Hello Gary, All
Gary & anyone interested: read on down below how I make my cap containers.
I think Oct 9th was a bad night for us coilers.
I, too, blew up my homemade cap. It was made with the strange thin stuff (prob
non PE) I had. As I already had finished the cap I thought why not give it a
try. Not gonna use the thin stuff again, tho. After ripping it apart I found
deep inside (only slightly moist with oil) a rash about 3" long, 1/2" wide and
about 3/4" into the underlying poly/Al sheets. I really destroyed this sucker.
No use repairing it.
My next cap will use the real PE (thicker stuff) and paper between each PE
layer.
BTW: Did anyone else out there blow up or destroy more precious Tesla stuff?
After about 10 minutes of intermediate running the spark gap quit and I heard
a nice sizzling sound coming from my cap. A few seconds later my cap went:
burp and spilled about a half a gallon of oil on my garage floor. It was great
fun cleaning up this mess. (Yeah, I know I SHOULD have put a container
underneath the cap to catch the mess, BEFORE it burped...oh well)
Now to safety valves. I used an "automatic" safety valve.
Hereīs my cap construction:
I use a piece of PP pipe. Over here in germany this stuff is used for sewage
systems inside of the house. It is less brittle and much more impervious to
oil seepage (and it doesnīt change itīs characteristics after coming in
contact with oil) than PVC. Just about the nicest thing these pipes have is
that they have an o-ring gasket inside the ends. You just pop a cap into each
end and it is:
a.) Oil tight
b.) Vacuum tight
c.) Makes repairs on your cap a real breeze
The caps fit rather good and seal very well, but should the cap burp, do to a
failure the caps will just pop off, which is why my cap didnīt go BOOM and hit
me in the noggin after some pestering electron made itīs way through the cap
the wrong way around. . I usually donīt seal off the vacuum port, so any kind
of pressure or change in oil level due to heating effects will leave the cap
thru this vent. I usually connect a small hose to the vent and run it to a
container to collect any oil that might emerge from the hole. I seal my
carrige screws (connection terminals) via smalls o-ring.
Iīm sure you can get something similar in good old USA. You might wanna try
this.
Tesla List wrote:
> Original Poster: Gary Lau 10-Oct-1998 1204 <lau-at-hdecad.ENET.dec-dot-com>
>
> Hello All,
>
> I was eager to log some time on the extended-foil rolled-poly capacitors
> that I've documented on my new web site. This capacitor is two units in
> series, each using .04" thick LDPE dielectric. The caps were housed in
> 4" PVC SDR pipe and had no provisions for pressure relief.
>
> Last night I ran the coil for 1 minute, checked for any signs of cap
> heating, ran for 2 minutes and checked. The ends were just slightly
> warm. I ran for 3 minutes and checked. The ends were again just
> slightly warm. I was about 2 minutes into the next run when the roar
> diminished, then POOOMMM! One of the PVC end caps burst, leaving about a
> pint of mineral oil on my garage floor and egg on my face.
>
> A post mortem disection revealed dielectric puncture under the long edge of
> the recessed foil, plus a slight discoloration of the poly elsewhere
> along the recessed edge of the foil, suggesting that the dielectric
> thickness may not have been adequate. All poly and foil surfaces were
> evenly wet with oil. Unclear is how long this cap would have survived
> had I limited run-time to a more conventional 30 seconds at a time. Is
> running 7-8 near-continuous minutes something that is foolish even with
> the most robust capacitors?
>
> I will update my web site with this info, and in the future, recommend
> and use pressure release mechanisms on caps!
>
> Gary Lau
> Glum in Waltham, MA USA
> http://people.ne.mediaone-dot-net/lau/tesla/tesla.htm