Very durable electrolytics or similar?

You're going to have this thing submerged in liquid nitrogen to get that kind of performance of these parts with any confidence.

125C/2000h isn't that great though. I'd rather go with 150C/2000h.

--
Regards, Joerg 

http://www.analogconsultants.com/

There's something to be said for that kind of scaling, but an electrolytic capacitor can fail due to non-chemical aging, i.e. seal failure. And, seal failure might be avoided by using a solid electrolyte (i.e. plastic). Consider Nichicon's CS series,

For seal failure, temperature cycles might be more important than temperature dwell time.

Are they with solid electrolyte? I can't find that information in the datasheet.

In our case there will be one very slow cycle per day, the long dusk to dawn phase.

--
Regards, Joerg 

http://www.analogconsultants.com/

--

Of course, any important data would be confidential, but I still think that you could have given much more information, without revealing who your customer is and what exactly they are trying to do.

While 10 years is the minimum _contractual_ life time, in practice industrial systems work for 20-30 years.

Ok, but I'd have to know what it is that you guys want to know in addition :-)

Aerospace usually shoots for 30 years of practical life. There's still DC3's in regular scheduled service that are over 70 years old.

--
Regards, Joerg 

http://www.analogconsultants.com/

I found it with DigiKey's search on capacitors-> aluminum-polymer so I guess so. I was actually hoping to find 'solid electrolyte' in the search tree. Like you, I didn't see any clear indications in the data sheet.

You can search on type = CS, but not on type = solid electrolyte. Website purgatory!

Lately Digikey has been inaccuate a bit. Mostly just wrong product photos but I've also seen stuff miscategorized in searches. Like radial fans coming up after keying in "gate driver".

Yet I won't complain. When I think how tedious design was in the 80's versus today it's like day and night. If you couldn't find a particular databook, none of the colleagues knew where it might be and it was after

5:00pm you could as well just go home. Now you can go all night because it's all right there on the web.

--
Regards, Joerg 

http://www.analogconsultants.com/

The point is that the "past" point was already reached, WRT aluminum caps, so polymers are needed.

But aircraft get regular maintenance. How many of those flying DC-3s have their original electronics (or engines)?

Discovered a funny the other day... try searching "s0t23" or "s0t-23" (that's a zero). Probably some guy just had a long day filling in those fields. :)

I'd be useless without the internet. Then again, sometimes I'm useless

*because* of it. :-)

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com

I have a 400-year-old hammer. Of course the head has been replaced a few times, and so has the handle.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

s

If I solve q = [? ? (Th^4 - Tc^4) Ac] for Th, where ? = .93 (emissivity of asphalt) ? = = Stefan-Boltzmann constant = 5.6703 10-8 (W/m^2 K^4) Ac = 1 m^2 Tc = 35 C (= 308K), q = 1,000 W/m^2

I get Th = 136 C. Did I goof?

Cheers, James Arthur

I want to say Phil's assuming Ta=0 degK, but I can't duplicate his calculation.

On the other hand, I posted a link with FLIR pictures and a set of measurements from Phoenix, Arizona. They say they've measured "as high as 172 deg F," which isn't even 100oC.

It was a lot hotter than 115oF--Ta was nearly that high all by itself-- so it's not an F vs. C problem. But I'm sure where I was wasn't any hotter than AZ. So, I must not be remembering accurately. I'd re-check if I could.

The problem was similar to Joerg's application though--I wanted a decade life in a sealed box at wicked high temps, and couldn't find any primary or secondary cells suited.

Cheers, James Arthur

George Herold"

** FFS - go f*ck yourself.

You pathetic, asinine, ASD f***ed TROLL.

.... Phil

Ten years ago, I rewrote parts of the control system for a VFD park, initially installed in the 1970/80s. Now I have been asked to update the control system so that it runs on current control system hardware. The VFDs and the motors are the same as in the 1970/80s.

Some of the motors might even be some odd DC variable speed motors prior to the semiconductor age :-).

Yep, the flat plate solar collectors I saw hissing and making steam were probably shiny (low emissivity) (and also insulated) on the back side of the plate, which would reduce radiation from the back surface and account for higher temperatures than in your calculation. As I already mentioned, the earth (and to a lesser extent the sky) are warmer than absolute zero, which will radiate some more heat onto practical objects and push the temperature a bit higher than the simple formula would give.

Also I found out that the wavelenth selective coatings that are high-emissivity in the solar wavelengths and low-emissivity in the long IR wavelengths have been around since the 1950s (though probably not actually used in commercial solar hot water systems for that long).

Chris

I am getting confused. I had thought heat only flowed from hot objects to cooler objects. Are you saying that the warm earth and surroundings will heat up Joerg's hotter enclosure?

piglet

Not as such, but if the earth (and in particular the ground around the box) were at absolute zero, then the box would be cooler than it is with the earth at the usual temperature. So having the earth warmer than at absolute zero does make the box warmer than it would have been if the earth were at absolute zero, but on balance heat is still flowing from the hotter things to the colder things.

I suspect that it is probably more accurate to say that heat is always radiated in both directions between two objects, both from the hotter one to the colder one and (to a lesser extent) also in the other direction. Otherwise each object would have to know whether there is a hotter object in a given direction before it decides whether to radiate photons in that direction. That would be complicated, and bearing in mind the speed of light it might be tricky to know what will be in a given direction when the photons would get there (especially for astronimical objects). It would be simpler to say that the thermal radiation goes both ways in all cases, but that the amount of it is more in one direction than the other.

Chris