bipolar aluminum caps

That's interesting. Does it imply that Al electrolytics can withstand short bursts of reverse voltage, as long as the average is substantially the correct polarity?

If so, I wonder how long they'd withstand a reverse - seconds, minutes - I suppose it would be stated as volt seconds per farad?

Cheers

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Syd
Reply to
Syd Rumpo
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Sure! You might want to put a fuse in series with it though. ;-)

(The intended joke is non-obvious. Do the unit analysis! :) )

Tim

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Reply to
Tim Williams

keeping time down isn't the issue. Keeping i down while the oxide forms is. I've not tested it, but guess C reduces when they're reverse formed.

NT

Reply to
tabbypurr

Yes, the capacitance won't come into it if I'm considering a voltage. Volt seconds alone is too simplistic.

What units would be appropriate?

Cheers

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Syd
Reply to
Syd Rumpo

Perhaps in the sense of being partially conductive. But not, I'm pretty sure, in the sense of being able to form a rectifying junction, much less a BJT or FET.

(I wonder if you could make a copper-oxide BJT -- I know it'll make a rectifying junction.)

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Tim Wescott 
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Reply to
Tim Wescott

It's the inexpensive option if you want 45 kV working voltage; heck, the 'lossy' ceramics are excellent at energy storage. The problem is, scaling down to low operating voltage,

stored_energy = V^2 C/2

At low V you need large capacity values which are made using nanostructure objects (supercaps, wet-slug tantalum, aluminum electrolytics and MLC caps). Letting a bit of leakage current build/rebuild your insulating layer is a big reliability and fabrication-cost win. MLC capacitors have to have plate separation of a few microns, with good uniformity, over a LOT of area. The electrolytics just need to generate an oxidized patina on the surfaces to accomplish the same thing.

Reply to
whit3rd

Any experience with gyrator ? Make your caps with coils.

Kind regards,

alpibucky

Reply to
alpibucky

Hmm, probably just charge. Should be independent of voltage rating, but proportional to capacitance, so, you'd have a ratio of charge to capacitance....... which is a voltage, but not the rated voltage. :o)

The amount of "voltage" necessary to reform the cap, may depend on the rated voltage as well (higher rating = thicker oxide to form / reform / deform). In which case, dividing by that gives a dimensionless "electrolytic reform" voltage gain!

Tim

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Seven Transistor Labs, LLC 
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Reply to
Tim Williams

Not counting chemical quirks, like non-stoichiometric compositions leading to uncontrollable doping (AFAIK, it's unreasonable to make N-type ZnO, because of excess oxygen?), and the different kinds of bandgap (direct vs. indirect), and some other things I forget -- it's just a matter of temperature. A semiconductor is any old insulator with a conveniently low bandgap, sufficient to allow a usefully small amount of thermally freed charge carriers.

I want to say, transistors were first discovered in Cu2O, late 19th century. I can't seem to find a reference to it, though. Lillenfeld made some interesting patents in the 20s, but they were poorly understood, and technically impossible, until years later (it took two score until FETs entered commercial use).

Without advanced materials science, and theoretical knowledge to back it up (you say it has to be HOW PURE!?), such observations were lucky coincidences, easily written off as shoddy work.

It's just as well; no existing infrastructure could have used them. ESD/surge from telegraph lines would've quickly toasted a point-contact transistor, if they even lasted long enough (between mechanical creep and atmospheric contamination) to perform any useful amplification in the first place.

Tim

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Reply to
Tim Williams

back to back electros in // with back to back diodes for improved reliability

Reply to
David Eather

and there Phil has it 24hrs earlier

Reply to
David Eather

Bipolar implies need for medication to achieve a semblance of sanity.

NON-polar, on the other hand,is what you mean. Nonpolar electrolytics have been around since before 1940 and it seems the lifetime (degradation due to heat,etc) has been comparable to polarized electrolytics. At least up into the'80s when i stopped seeing them. Did no repair work on speaker cross-overs,where they were "common". There is no reason that a nonpolar polymer aluminum capacitor would be worse. In fact, i would expect better longevity and reliability. Availability may be rather low due to a small market like speaker cross-overs. But, there is no reason you cannot use the age old trick of back-to-back caps.

Reply to
Robert Baer

  • No more than singles. A smaller mylar in parallel can do wonders.
Reply to
Robert Baer

A monopolar tantalum is shit at inverse voltage, and you take the risk of explosion. Even if you do the standard of derating by an order of magnitude.

Reply to
Robert Baer

Yes; that is the "standard trick" of order-of-magnitude derating. But even so, still having the possibility of fireworks.

Reply to
Robert Baer

When I was in IBM, we used tantalums by the millions (perhaps a thousand per system). The only problems we ran into were reverse insertion but that could be spectacular and occur years later. Our design ground rules called for a voltage de-rating of 2-3 times (no more), not much different that ceramics (though for different reasons;-). We didn't use aluminums. These were 100K hour applications.

Reply to
krw

Your "standard de-rating" is *way* to high.

Reply to
krw

if you can control peak current they're fine. The problem is many have thought current was under control and found later due to tant failures that it wasn't.

NT

Reply to
tabbypurr

Used as bypasses for 1KA supplies, there wasn't much current control. They were fine, as long as they were inserted and de-rated properly.

Reply to
krw

Do not complain to me when a problem happens...

Reply to
Robert Baer

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