Silly tantalum cap question

[Mark Hammer]

Rummaging through my drawer of tantalum caps, I come across some 68uf caps that seem just right for decoupling power, except for one thing: I have no idea what their voltage rating is.  They seem big enough, but the voltage rating indicates 10k.

Is that 10000V (unlikely) or 10V (more likely) or something else?

[digi2t]

From I've seen on the net (different datasheets) "10" is for volts (10 volts), and "K" designates case dimensions.

No such thing as silly questions my friend... only silly answers.

Hope it helps. If I'm out to lunch on this one, let me know.

[metallo]

K usually indicates +-10% tolerance to their value. http://wiki.xtronics.com/index.php/Capacitor_Codes

Picture?

[Mark Hammer]

Hmmmm, interesting conundrum.  I may just have to post a picture to get it resolved.  I'll try later this evening.

[cjlectronics]

Years ago, in my engineering technician days, I accidentally put some tantalum capacitors in backward.  When the engineer and I fired the board up, i never knew the engineer I worked for could run that fast!!  Those caps were the next best thing to black cat fire crackers.  Good times!!

CJ

[Mark Hammer]

Well happily, these have a very visible + sign on them!

I'm not in a position to post pics tonight, but after looking at all of them, there is only the "686" (indicating 68,000,000pf or 68uf) and "10k" marking on them.  They are a wee bit bigger than the 100uf/3v, 4u7/6.3v, and 10uf/25v in the same bin, so I'm thinking these are 10v.  My experience is that for tantalums, moreso than for many other types, size tends to track value/rating.

[frank_p]

I don't know if it's just me but, I am not seeing a lot of tantalum caps that are rated over 100V...  maybe even: not much over 50V...  Curious.

[R.G.]

So Mark, put some voltage on them and **take pictures** when they let go.   

[amptramp]

I don't know if it's just me but, I am not seeing a lot of tantalum caps that are rated over 100V...  maybe even: not much over 50V...  Curious.

The highest I have seen is 75 volts.  Anything above that is usually two capacitor slugs in series.  Note that dry slug tantalums are NOT suited to power supply bypassing unless there is some series resistance.  They tend to explode without it due to the transformation of tantalum pentoxide (non-conductive dielectric) to conductive tantalum dioxide at high temperatures.  If a defect site has a temperature rise, some material is converted.  If there is enough current, the conversion sweeps through the slug like a firestorm and you get an explosion.  With enough resistance, the amount of current is not sufficient to convert more dielectric and the defect site shorts locally but does not explode.

[PRR]

The natural breakdown of aluminum oxide is 400V-500V. Breakdown of Tantalum dielectric is much lower, though I can not find a citation.

That's why Al goes up to 400V, 450V, sometimes 525V, but no higher (except as stacks packaged as a single unit, the old 700V caps), and Tantalum doesn't go much past 68V-75V.