I have now toasted one of my two maxwell's, as well as one of my
four strands of CDE 940C's. In the interest of not blowing up too
many more capacitors, I am trying to do my research this time before
ordering their replacements (and not using any of the remaining
caps, for this coil anyway).
unfortunately finding a few roadblocks to that end:
1. I have a possible source of doorknob caps, in the form of another
pacific northwest coiler who I recently bought a pole pig from, who
is going to try to acquire some soon. However, I have heard doorknob
caps might not be as effective, not to mention they are going to be
HEAVY to get enough of them for a 25KVA pig powered coil, which is
using a 120BPS synch rotary.
2. Have a rell.com shopping cart, containing 90x CDE 942C's (the -F
version, which they have in stock, not the non -F which has a lead
time of weeks). however, that is a $300 order that will still only
have the same voltage rating as the 940C's which failed QUICKLY when
I used them last week. A safer voltage rating would require more
caps, and would still be less than the resonant cap voltage by about
1/2. .06 uF is what the 2 37667's I was using added up to, with
great results, so that is what I was aiming for this time. LTR
according to JavaTC is something closer to .48 uF (hmm... $2400
worth of 942C's, even if I only use strands of 15! I think I am
going to pass on that option).
3. Maxwells- I would love to find out more about Dr. Resonance's
better Maxwell caps, than the 37667's which are known to fail easily
in a 25kva pig powered coil. (Between Aaron and I we have fried 2 of
the 3 maxwells that I have ever seen in my life, both within the
last month or two. ) Unfortunately all I can find is part numbers
and ratings, nobody selling anything other than the 35 kv .03 uF
37667's, and even those are $225 where I have seen them. Does anyone
know of a current source for better maxwell's, and/or have other
recommendations in this area?
4. Any other options? I haven't found any that don't involve a
custom order from CSI (which doesn't seem to take me seriously,
judging from their lack of a response to my recent request for
quote). I didn't even mention that I would be using it for a hobby!
So, in lieu of having many other options, I am starting to lean in
the direction of building my own. I have tried this in the past but
didn't know what I was doing, at all, last time. This time I am a
bit more educated, prepared, and have a more impending need now that
everything else in my coil seems stable including for the first time
ever a synchronous rotary.
For building this cap, I have a vacuum pump that will pull 29+
inches of mercury, and a t-shirt press which may help between the
two of them to remove air bubbles. I was thinking that if I ordered
a roll each of these two, I might be able to make enough caps that
are both fairly efficient, and high capacitance/ voltage, that I
could replace the maxwell/ MMC with something not too much larger,
in the overall scheme of things.
<http://www.papermart.com/Templates/47-0-40.htm>http://www.papermart.com/Templates/47-0-40.htm
(a 100' roll of 30" wide metallic .8 mil polypropylene sheet)
<http://www.papermart.com/templates/47-0-15.htm>http://www.papermart.com/templates/47-0-15.htm
(a 500' roll of 30" wide clear polypropylene 1.2 mil sheet)
(multiple layers of, between each layer of the above.)
I figure if I do a careful job in the overlapping, and use some
mineral oil or something to pot it once the whole thing is rolled up
in a tube and wires attached, I would be able to make it fairly
robust. I even thought about making it in a sandblasting chamber
that was completely cleaned out, and had an argon tank hooked up to
it or something to purge the air (and corresponding particulate) out
of the chamber after putting the parts in it, then sealing it before
working on assembly. but that is way overkill considering it
wouldn't even fully do the job- better just to use multiple layers
of clear polyprop between each metallized layer, and leave large
areas of clear overlapping all 3 edges of the metallized, and most
of all removing every single air bubble by pulling a full vacuum for
a few days after filling the tube with oil. then maybe a little more
oil, an over-pressure safety valve for when the oil gets hot enough
to raise the pressure inside it, and it should be decent enough for
a run or two of the coil, right?
Definitely has to be better and smaller than a fishtank with 2
half-racks of saltwater filled/ motor oil covered corona beer bottles in it.
please give me feedback if you think I am nuts or could do this
better another way or using something off the shelf. Regardless of
what option I choose, I only budgeted myself about $400 to spend on
replacement caps and I am hoping to use them more than once. I also
don't feel like waiting more than a couple weeks for something which
is on backorder so that rules out at least one option.
thanks in advance,
NICK