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  • Author Author: baldengineer
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Guess the (Former) Capacitance Puzzle [SOLVED!]

baldengineer
Guess the (Former) Capacitance Puzzle [SOLVED!]

Without any question, my favorite passive component is the humble capacitor. For many of us, our first introduction to capacitors is learning that there are two types: non-polar and polarized. The next lesson we learned is that you do not want to apply voltage in reverse to polarized capacitors! Well, to heck with that. I did it anyway.

(Note, this video has a slight flicker from being shot in slow motion.)

Why does this happen?

Aluminum is a "valve metal." A property of valve metals is that their oxide grows in the direction of an electric field. During manufacturing, the aluminum anode sheets go through an electrolyte bath with a voltage applied. Together, this processor forms an oxide layer (Al2O3) which is an insulator and creates the capacitor's dielectric layer.

When the electric field is reversed, guess what happens: the oxide breaks down! And what is the oxide made of? Oxygen! So, two things happen. You start to get a build-up of free oxygen molecules. And the dielectric gets thinner. Eventually, it gets thin enough that current starts to pass through it. And what happens as the current goes up? You get heat. So now you have gas building up in a tightly closed container with the presence of heat!

In the cases where failure occurs from the gas building up, the can/vent usually just pops. In the more extreme case, you get rapid deconstruction.

Guess the Capacitance (and Voltage Rating)!

Can you guess this capacitor's (former) capacitance and voltage rating? Get it right, and you can win a DMM! Answers will be judged on getting the two ratings correct and how you came up with the answer! (So, show your work!)

Hint

2023-03-28 Update: This capacitor blew with a reverse range of -10 to -32 Volts. 

The reason for the range is that I tested three pieces. In all three cases, the rate at which I ramped up (or down?) the voltage had an effect on when it would blow.

What might not be intuitive is that the slower you ramp, the lower the voltage it will die--usually. The slower ramp gives more time for the dielectric to break down. Also, if you go really slow, the can will not explode. The gas has enough time to escape through the deck seal to prevent extreme pressure. The result is a small pop with no flying components. (I didn't bother saving that boring video.)

For what it is worth, I think the extended explanation sounds cool (to me, anyway), but it probably does not help. Slight smile

Final Update: Winner Announced

Not only was there only one correct guess, even from those who gave ranges, but it was the last guess before the end of the official timeline!

The capacitor in question actually measured 106 microfarads before it ceased being a capacitor. And it was rated for 16 volts.

Now, even though I was hoping someone would try for the actual capacitance, I assumed most people would guess an E12 or E24 value.

Congratulations to  ! You got the right combination.
Someone on the e14 staff will contact you regarding the prize!

Thanks to everyone who participated. Several of your responses made me smile with your attempts to solve it!

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