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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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