Re: Why doesn't everything use solid aluminium capacitors?

Cost is only 20% higher. Lifetime is many times greater.

Not compared to the types of capacitors check out the data sheets typically up to 2000 hours.

You have to apply the Arrhenius temperature correction to those service hours at high temperature.

In chemistry, Arrhenius is taught as if it's a monolithic thing. Every 7C (10F) rise in temperature, doubles reaction rate.

In electronics, something different happens. Arrhenius exponential is curve fitted, and the doubling rate for reliability, differs depending on topic area. The doubling is around 15C or so for curve fit of electrolytic capacitor reliability. You use the curve fit data from the manufacturer, to correct the service hours at a lower temperature.

If the capacitor operating hours are five temperature-doublings lower, then the service hours would be 2^5 * 2000 hours or 64000 hours sitting inside your computer case with the fan running. It's not that warm in there.

When quoting the 2000 hour number, you also have to include the temperature at which the number is quoted. A capacitor quoting 2000 hours at 105C is better than a capacitor sporting 2000 hours at 85C. You have to adjust them to a common temperature, and then compare the hours, for a fair comparison. Maybe the one at 105C is four times better than the one at 85C. As a rough number pulled from the air.

When you get those catalog numbers, it would pay then to find the appnote where the manufacturer has characterized the devices, and extracted the temperature necessary for a doubling of reliability. Be it 15C or whatever.

Paul

Anything with only 2000 hours is not fit for sale. That's going back to the days of the filament lightbulbs.

At the temperature of the surface of the sun, the lifetime of the capacitor is 0.1 milliseconds. While you're sitting on the surface of the Sun, a spherical cow flies by.

At 105C, the capacitor lasts 2,000 hours (as communicated in some military reliability handbook or similar). The numbers selected, are intended by the manufacturer to resemble "classes of applications". Military, industrial, consumer.

At 45C, the capacitor lasts 60,000 hours. This is the temperature inside your PC, on a particularly hot summers day. A day so hot, you've stepped out of the computer room, to go for a swim down at the lake.

The rubber seal on the cheap capacitorss, is rated for a 17 year lifespan. Which is an issue that "runs in parallel" with the accelerated life testing curve being communicated above. If the room is filled with concentrated ozone, the cap lasts a day or so, before the seal is gone and the cap now has evaporating electrolyte.

The behavior of the reliability number, follows an Arrhenius style equation, with suitably extracted empirical constants. This requires the engineer in the lab doing the measurements, to own some "curve fit software", because nobody writes this software for themselves any more. (Although we were taught how when I went to school. Not that this matters.)

Paul

They're not used there.

WTF?

Rubbish. I've got graphics cards approaching that temperature. 2000 hours is only 83 days, that would fall foul of the warranty.

Really? Capacitors tend to be next to power circuits, they're much hotter than that.

Which is why I said we should be using the solid ones. I see no seal on those.

But you'd suffocate first.

You're a university graduate with a physics degree, and you don't know what a spherical cow is ?

Paul

There's more than one branch of physics. I didn't do (but wish I had) astrophysics.

Hows it going Hucker. Have you got a job yet.

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