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Re: [TCML] Maxwell 31173 fail
Wow!
What max. pulserate bps was this cap designed for? I cannot see the typical
extended foils at the ends of the caps inside.
Some years ago I disassembled one of my 40kV/650nF/20nH maxwells because I
have plenty of them. There I could clearly see the extended foils and
massive busbars contacting them. By the way, these maxwells contain
ricinus-oil.
Maybe your Maxwells are not designed for arround 1000pps and they have to
much inductance?
Stefan
----- Original Message -----
From: "Joe Mastroianni" <joe@xxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, February 12, 2011 5:23 PM
Subject: [TCML] Maxwell 31173 fail
<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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