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First and foremost, I'm going to say that I do and plan to continue to follow all safety best practices for working with electronics. I'm also a relative newbie, so I don't have a lot of experience diagnosing WHY things fail, and especially not in creating deliberate types of failures.

That being said, I'm helping a friend make a few short videos to augment an electronics workshop he does. The workshop is a very basic overview of electronics, more to get kids interested in the possibilities than an introduction to electrical engineering. With my background in graphic design and A/V production, he's enlisted me to make his powerpoint presentation more dynamic. I'm adding some short animations and video clips illustrating electrical concepts.

One video that I want will show power being applied to a circuit and then having the circuit smoke and fail after a short delay. We have a couple things we want to communicate:

  1. electricity is dangerous (if this happens on a small scale, imagine the disastrous results on a larger scale),
  2. the delay will show that failures may not be instantaneous, BUT
  3. don't let that stop you...everyone's encountered a blue smoke monster, fix it and move on.

LED flareups (see how easy it is to burn out an LED by simply mixing up where the anode and cathode land?), aren't nearly as visually dramatic as I'd hoped, but I do recall making something from a kit about a year ago that just smoked like crazy once I plugged it. I'm not sure what component failed, and it's dead on my workbench waiting for a diagnosis...but it looks AWESOME. So I'm looking for a circuit; I envision a PCB or breadboard with a couple components, I attach a power source (AA or 9v battery), and after a few seconds, smoke. If there's an LED that blinks out after the smoking begins, illustrating that the circuit is dead...that'd be awesome. And, being the perfectionist I am, I'd like to be able to reproduce it reliably for multiple takes.

Any suggestions for a circuit that'll do this without unnecessarily endangering myself?

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2 Answers 2

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As usual, you need look no further than the eevblog exploding capacitors video

AND, OF COURSE, AS A WORD OF CAUTION:

-wear safety glasses

-keep flammables away

-test out everything first with a proper DC voltage supply that has effective current limiting and safety measures

-do it in an actual lab that has real safety and hazard precautions

Not following any of the above is probably not smart [but probably how I would do it anyway ;).] With a low voltage, the biggest danger is probably to actual projectiles.

I would just reverse bias a low voltage cap (for the most flare up). You can put a diode somewhere after it that will 'turn off'. I would also put a current limiting circuit at the input to kick in after the cap goes, for safety.

You could probably get some nice smoke from any IC that you overvolt with a decently rated supply current.

You may need more than a single AA or +9V to get this effect.

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    \$\begingroup\$ Be careful overvolting an IC. I've seen the plastic case leave a voltage regulator at something close to the speed of sound : fortunately missing everybody. \$\endgroup\$ Dec 16, 2013 at 16:51
  • \$\begingroup\$ We used to power up our new revisions of 500V fet boards behind an inch of lexan! \$\endgroup\$
    – scld
    Dec 16, 2013 at 18:39
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    \$\begingroup\$ Capacitors explode spectacularly and dangerously. ICs can be unpredicable. A simple 100 Ohm 1/4 watt carbon comp resistor should give you a nice repeatable smoky burn. An adjustible power supply would let you adjust the voltage to get the desired burn rate. \$\endgroup\$ Dec 16, 2013 at 19:17
  • \$\begingroup\$ -12V from a 5A supply across a 3.3V 220mF supercap can have spectacular results. Not what I'd call "safe" though... \$\endgroup\$
    – markt
    Dec 16, 2013 at 21:27
  • \$\begingroup\$ Also, I feel like I need to request that the video be made in classic infomercial style and posted for all to see. Someone in a lab coat plugging in a comically oversized plug the wrong way and a big puff of smoke. \$\endgroup\$
    – scld
    Dec 17, 2013 at 16:03
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There is no reason to be absolutely authentic. Especially if you are doing multiple takes to get it right and want repeatability so you can perfect it. Think of yourself as being sort of like George Lucas and the special effects for the first Star Wars. (There's a special edition version of Star Wars that I'm thinking of that documented how they did the Lava planet, Mustafar.) There is no reason why you can't have some pyrotechnics mixed in with your exploding capacitors. Just like Star Wars, you're creating an experience, and it's the experience that has to be real, not the "accidents" behind them.

And you could synchronize it with an on-board Arduino chip you transplant in using an on-board socket for replaceability if you toast it, turning things on using opto-isolators and relays.

I'm envisioning a sparkler cut up into 1 inch sections, wrapped with a bit of wire much too thin for the current you're going to put through it.

As a kid, I remember the neighbor lighting smoke bombs behind our house. A little bit of that material heated to a suitable temperature will probably do wonders for your presentation.

But here is where you're going to have to show restraint -- it might be tough to make them think it's real, but that's your true goal... ...so no RAINBOW-COLORED smoke, right? (Is there a fireworks and pyrotechnics stack exchange, does anybody know? ;-)

Oh, yes, I almost forgot, a good transformer can always take a higher voltage with low current, and produce a low voltage with high current (which is what they do for welding, for instance... melted metal makes quite an impression, especially if they pick out a steel nail, and you give it back to them in pieces, cooled off of course).

A microwave oven transformer with the secondary (the high voltage one) replaced with a few turns of, say, some good jumper-cable from Walmart. Google "King of Random Microwave oven Transformer metal melter" or "MICROWAVE OVEN TRANSFORMER ULTRA MOD" to see what I'm talking about. And as long as the body of the transformer is well-grounded (I believe -- I'd like some agreement on this though... anyone?), it shouldn't be dangerous from a voltage perspective, because...

I actually built one which has about 3 or 4 turns on it (out of some repurposed jumper cables) and it only puts out about 3 AC volts. Melting metal or Welding with it is safer than regular welding because it's really low voltage (but really high current).

And the hum the transformer generates as it melts the metal will make quite an impression on them for the rest of their lives. I once hooked a little 9-volt battery up to a transformer and got a tremendous shock, and thinking back, that's probably why I'm still fascinated about electricity today.

Finally, you can use regular goggles (don't need the darker welding shields), because it doesn't produce the ultraviolet that the higher voltage does (not as much plasma, but plenty of sparks, and molten metal, which are, yes, both dangerous). The lower voltage does mean that the secondary gets more of the heat. Microwave oven transformer, humming, melting metal, and making sparks. That's my best idea. Let us know how it goes.

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