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Re: [TCML] Maxwell 31173 fail



Hi Joe,

Yikes - thanks for sharing the pics!

The combination of RF AND high break rate probably killed it. Most of Maxwell's 31XXX series caps are rated for only 1 PPS. Looking at the capacitor's relatively small physical size versus its voltage and capacitance ratings, I strongly suspect that Maxwell used a polyester (Mylar) dielectric system in your cap. A polypropylene cap of the same rating would have 2-3X the volume.

Although Mylar pulse caps can handle short runs in TC's if they're allowed to cool down between runs, sustained running will rapidly cook them from the inside out. The GOOD news is that the PP case on your cap failed "gracefully". Cylindrically-cased pulse caps (made by some other cap manufacturers) sometimes exploded when they failed. In any event, exploding or melting your first tank cap is a rite of passage - a "learning experience" that you (and your spouse) will remember forever. My wife has witnessed two cap explosions, and was NOT amused by either of them... =:^O

If you request (or already have) the Maxwell data sheet for your cap, you can find the abbreviation for the type of dielectric impregnant they used. Maxwell's abbreviations include:

CO  = Castor oil (vegetable oil)
RSO = Canola oil (vegetable oil)
IPB, IPBP, MIPB = Monoisopropyl biphenyl
PXE = Phenyl xylyl ethane or diaryl alkane
SO  = Silicone oil, (polydimethyl siloxane)
MO  = Mineral oil (petroleum-based)
EPX = Proprietary - contact factory
TCP = Tricresyl phosphate
DOP = Ethyl hexyl phthalate (dioctyl phthalate)
DRY = no oil

Although messy (and possibly stinky), none of these fluids pose a major hazard, but some may irritate your skin. You may want to wear disposable nitrile gloves during cleanup - latex will dissolve in some of these fluids. You can get more details by downloading the MSDS sheet for the impregnant used in your cap.

BTW, nice looking coil!

Bert
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Joe Mastroianni wrote:
<http://www.flickr.com/photos/iceowl/5437138473/> New
resonator<http://www.flickr.com/photos/iceowl/>  and topload
combination.

Yes voltage reversal.  Yes maximum pulse rate.   Of course. One
learns about these things, then forgets, then relearns after the
catastrophic failure.  The wife said, "Look, smoke,"  and I said,
"@#$(!" Like others before me, it took some number of measurable
seconds to shut everything down, during which time the coil continued
to operate "normally" even with it's guts spilling out.

The cap has been working swimmingly in with the new resonator and
pole pig power supply (being run above it's 5kVA rating at about
9kVA). ARSG running at around 300bps.  Of course, unhappy with
stasis, I began tweaking the tuning.  Why?  Oh, because.   JavaTC had
given me a precise number, I tuned to it, everything was hunky dory,
and then I tried to change it, just to see if things would get
"better".  They didn't.

I tried setting various breakout points.   They worked.

I tried running without breakout points.  It was much more dramatic,
though the arcs hit the primary , and I got a couple ground strikes
which killed the rectifier running the ARSG DC motor.

(By the way - this happens ALL the time.  Ground strikes trash my 30A
rectifier running a 90VDC 1.5hp treadmill motor.  That takes out the
fuse in the variac running the motor, and the now powerless motor
starts slowing down.  If I am not vigilant, the RPMs can change
dramatically before I can hit the panic button.   I've been
discussing this with Dave Leddon, who notes it is a common issue in
this kind of coiling.  If anyone has a "fix" for this phenomenon - I
am ALL ears.   My fix is to keep a box of 50 rectifiers  and 50 12A
fuses around.  I've gotten to where I can replace everything in about
90 seconds - but it's such a pain.)

I tried jury rigging a strike rail - at which point I learned that
jury rigged strike rails placed too close to the primary become
little resonators of their own.  Ok, bad idea, Joe.

Then, the wife came home from work and saw she couldn't park the car
in the driveway.  She said, "What I great way to come home to a lousy
day at work!" and really meant it, which is why I love her and
married her as soon as I could.   She was all smiley and giggly,
because the coil topload looms over her now at a height of about 8.5"
(she's short), so when we are prone to flights of whimsy it seems
we've really built some sort of very important reality-warping
machine.  She needed some sparks as much as I did, so I fired up the
coil and started messing with the ARSG speed.

I sped it all the way up to the max RPM - watching the sparks fade to
nearly nothing, and then slowed it down.  Spark size maxed at about
2400rpm (1/2 speed which = 300bps), and then just for the halibut I
slowed it down even farther.  There was no effect at lower BPS rates,
and higher or lower voltage settings, right up until the wife said,
"Look, ahhh!"

There was a rather large puff of brown-gray smoke.   The coil kept
sparking, and it was at least 2-5 seconds before I realized what was
happening and the panic button killed the power.

The capacitor (as you can see from the pics) exploded through its
casing.  It was a steaming hunk.  Very warm - clearly internal
stresses from heating caused some expansion.  There was oil oozing
all over.

Etc.

Well, maybe this is a sign it's probably time to start on my DR power
supply.

Cheers,

Joe


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