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Most spectacular failures

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joshua_

Mon Feb 20 2006, 08:57AM

Registered Member #61 Joined: Thu Feb 09 2006, 05:50AM
Location: Mountain View, CA
Posts: 43

We've all had projects that didn't go quite the way we planned. Usually failures aren't so bad to recover from, but sometimes, you really lose hard. This thread is about the latter.

I'll start: I had scrounged some CCFL inverters, and I was pulling arcs from them. They worked decently individually, but performance wasn't really great. I had gotten onto the idea of seriesing them (or paralleling them) for arcs longer than 2cm or so.

For those of you unfamiliar with the circuit, you can take a look at the schematic (sketched on a napkin, then eaglized -- I might've gotten something wrong, but it's about accurate, IIRC). That schematic shows the configuration if you want to run them in series. Particularly interesting is that the feedback windings are all tied together to keep all of the inverters in phase; else, you'd just end up with a mess with similar (or less) power. Also interesting is what appears to be a ballast on the output to avoid destruction in the case of exactly what I was doing.

Well, I decided that there was no need for all three of them in circuit -- I wanted the most power that I could get! So, I dutifully removed two and replaced them with short circuits. I powered it up, and drew an absolutely beautiful arc -- the most powerful I'd ever had from it. Had a nice white tone in the middle, and was probably .5cm thick. Dead silent. But as I was playing, the arc suddenly extinguished. I reached for my battery to jiggle the terminals -- sometimes the wires tended to fall off the top of the 7Ah SLA's connectors. As I reached, I heard a *click!*.

I knew instinctively what the click was; it was the sound of my ammeter's needle pegging. I looked over, and confirmedit. I tried one more time to strike an arc, and I noticed that there was no way in hell that the arc was going to strike. One of the transistors on one of the boards had quite nicely melted, and the others were about to go.

Evidently, that one little ballast couldn't handle the HV across it -- or, more correctly, the already slightly carbonized board below it couldn't. It arced over, and I suddenly had a very nicely huge current flowing through my secondary. Power, of course, remained equal, and the current shot up through the primary as well. That got the transistors nice and toasty, and one of them just stuck on. When the transistor stuck on, it also fed decent amounts of power into the bases of the other two attached boards, and cooked the transistors on those as well. As far as I know, the transformers are still good.

Your turn...

[e: fixed image size. darn, 400px width is teeny!]

ragnar

Mon Feb 20 2006, 09:45AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

I've had several spectacular failures, some off the mains, some off my banks of seriesed lead-acid batteries (a bad habit, I admit).

Generally if a project of mine fails when connected to SLAs (36-48VDC), there is pink, red, blue, grey, or black smoke and a bad smell.

If it's connected to the mains, there is blasting around failed components, the most wonderful 50Hz "BVVVT, SPLATTER SPLATTER, FZZZZ" etc, by which time I'm yanking in vain at my variac's extension cord.

Here's a pictorial exploration I drew a while ago:

lim-ape.gif

I generally try not to take photos of stuff that fails... cause it makes people think my circuits are unreliable =P

[Edit: Changed image to link. The rules say maximum 400 pixels.]

Wilson

Mon Feb 20 2006, 10:26AM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

I've had a full bridge burst into orange flames on me once which working on my induction heater.
and btw blackplasma, i think the smoke which comes out of semiconductors is poisonous, especially the colourful ones which you describe

Marko

Mon Feb 20 2006, 01:26PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

All smoke is poisonous...

Well recently I pulled an arc with my finger from miniature SSTC (1,8cm dia) from middle of secondary, blew a hole in it and my finger smoked as well...

I had lots of explosions when working on small SMPS supply, blew couple of mosfets and bipolar transistors, and when they fail short 400V 100uF capacitor discharges violently trough them, later I put resistors and inductors to minimize current but they didnt help a lot...

Transistors are trashed and only few are kept to show, didnt want to bother of taking pics of two blown transistors...

Steve Conner

Mon Feb 20 2006, 03:04PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Whee!

Michael W.

Mon Feb 20 2006, 03:15PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

I had a tesla coil strike to a power bar I had onboard and it caused a steady arc along with red/orange fire, 10 foot streams of vaporizing something, tons of scraping, burning and popping noises and melted 3 powerbar inlets.....

Marko

Mon Feb 20 2006, 03:41PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Its actually one of best ideas not to solder transistors (any) just screw them, hurts lesser when they explode

My graveyard...

HV Enthusiast

Mon Feb 20 2006, 05:16PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Here is one of my better failures caught on camera.

Marko

Mon Feb 20 2006, 05:33PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

When transistors blow and short large filter capacitors discharge few hundred joules into them with such results...

Even small 100uF cap made my mosfets burst across room...

Very good pic..

Avalanche

Mon Feb 20 2006, 05:47PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Here's a classic video I posted a while back

Maplin coil explodes

The bridge went short circuit, and freaked me out a bit when all the lights went out as well

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