10V ceramic cap at 95V DC ?

As you have seen

- Polarization gets lost (perhaps recoverable) and more

- Capacitance at that high voltage drops considerably

- At some point in time or at some higher voltage the part will spark or something like that

Bye

I was making a EFL inverter, it had some 1nf 1205 400v caps in the filter, when I was trying to get it to work ocassionaly the thing would resonate and get so excited sparks would jump acros the endcaps of the capacitors !

I was surprised the caps hadnt failed and gone short circuit, it was quite spectacular.

Ive used some 10uf ceramic caps in a low leakage integrator application, I measured the total leakage in the circuit and it was the same as the leakage through the glass fiber pcb. theres probably good reason why the guaranteed specs are seemingly somewhat pessimistic.

Colin =^.^=

Be careful if that comes off a low impedance source. I have seen ceramic turn into bubbly green glass with a loud bang.

ISTR some information (AVX site?) saying that most ceramic caps will survive several times the rated voltage, it is just that a few per batch may not.

Regards Ian

Sounds like Russian roulette ;-)

I only tested a couple of caps and didn't go higher that 95V on a 10V rated device. Its interesting watching such a tiny thing make a nice little blue spark when shorted.

Hmmmmm. Methinks I want to buy a reel of a thousand, build an automatic testing machine, and assemble the remaining ones (being made almost entirely of magic smoke, the bad ones remove themselves from the machine with the assistance of a small fan) into a rather large capacitor. Whaddya think, energy density comparable to aluminum electrolytic at least? ;o) Power density through the roof!

Tim

-- "Librarians are hiding something." - Steven Colbert Website @

of

in

second

may

College student :-(

Tim

-- "Librarians are hiding something." - Steven Colbert Website @

No, starving Contract Inventor. ;-)

Or, depending on how hungry I am at the moment, I can do grunt work.

Let's face it, who amongst us isn't a w**re, some of us merely priced higher than others? >:->

Thanks! Rich

The X7R and BK (and some other) capacitor ceramics are nonlinear (actually ferroelectric), and the problem with overstress isn't leakage or explosion. It's capacitance-value-droop. And as you saw, the value stays out-of-spec after the stress is removed. At 95V, if you'd measured it (put a known-good capacitor in series and voltage-stress it then measure the series pair under voltage), you might have found 0.2 uF.

A buddy of mine was trying to measure capacitors for a filter. He never got the same value twice from the digi-bridge. I saw the markings on the capacitor and laughed- it was the heat from his fingers as he handled the caps that made 'em always a few percent off on successive measurements. Nonlinear materials are great for energy density and in applications when you care little for AC dissipation. They don't really obey the straight capacitance equation very well, though.

That's an old Playboy Party Joke. The "real" Churchill quote, which probably actually came from W.C.Fields, was:

Dowager: "Mr. Churchill, you are drunk!" Churchy: "Madam, you are ugly. Tomorrow I shall be sober."

And then there's the one where a guy walks into a bar and sees a gal with a duck under her arm:

Guy: "Hey, where did you get the pig?" Gal: "That's an old joke!" Guy: "I was talkin' to the joke."

Cheers! Rich