Replace tantalum caps with aluminum?

Check the operating temperatures. The tantalums may have a higher operating range.

Tantalums are also made from slugs. Aluminum electrolytics tend to be wound; they may have some peculiar resonances.

Al

It's a low power device; basically sits pretty close to room temp.

Hmm. I'll take a look at the mfr spec sheets for the aluminums. Thanks.

If they are mostly working, you might measure the ESR now, and get an idea.

"Walter Harley" wrote in news: snipped-for-privacy@corp.supernews.com:

I suspect good low-ESR al. caps would work fine,and be much less expensive.

Thanks.

expensive.

May also be worth checking out the "Solid Aluminium" caps. These are different from the aluminium electrolytics. They have very low ESR (comparable to tantalums) and very long life.

Costas

Have you checked

"Walter Harley" wrote in news: snipped-for-privacy@corp.supernews.com:

If these are in the metal cans with the glass seal around the positive lead, then these tend to be VERY reliable and I would not replace them with aluminums under any circumstances. They are quite pricey, but if you should actually have a bad one, you should replace it with another tantalum.

These are a much better cap than the teardrop tantalums.

I've actually never seen one of these good tantalum caps fail, but I've increased the reliability of a lot of my gear by replacing failed (and commonly failing) low voltage alum electrolytics with these. If you keep your eyes open you can often get good deals on these at swap meets. I've been picking them up for years and now have a good supply whenever I need one.

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Electrolytics can have low lifetime specifications. I once saw a some with a spec of only 1000 hours. Thats about 41 days! Must have been a mistake?

No, just cheap caps. You need to select electrolytics with a higher temperature rating to get a longer life. In other words, the closer you run it to its rated temperature, the quicker it fails. Cheap caps are rated to 85°C, better caps are 125°C. You have to consider the operating temp of the equipment, plus the heat generated by any AC passing though the cap. A low ESR cap will generate less heat and last longer. Both higher temperature grade and low ESR cost more money, so lots of bean counters use the cheapest piece of crap they can sweep off the floor at the factory.

I believe I've read that lifetime doubles for each 10C under the rated temp. So if they were 1000 hours at 85C, then when run at 25C they'd be good for

So they probably put them in TV motherboards at 35C, and then the TV dies after 3 years and the owner buys a new one. The cap not only saves you money, it *earns* you money!

This has to be a mistake. Can you think of the hundreds of electro-caps used in each of every TV set and appliance???

--

Greetings,

Jerry Greenberg GLG Technologies GLG ========================================= WebPage

"Jerry G." wrote in news:bql6qt$nuk$ snipped-for-privacy@news.eusc.inter.net:

Look thru the Digi-Key catalog,the list the typical life of some of their electrolytics.I think that's a worst-case spec though.

Hi Jerry, No mistake but the rated life is done in hours over time at a given temp for so much change in value at a max. If ran that way most would still work longer if the circuit allows it but it would be a poor choice to use in that case. Jeff

Only if the customer is stupid enough to buy your brand again.

There is bit more to it.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs

...Unless the customer figures that all the other brands suck just as much.

Far as I can tell, practically everything out there these days is made to the same low standards. It all seems to be a race to pinch every last $0.01 out of the retail cost, regardless of whether it halves the useful life of the device, makes it less usable, or what. Except for "audiophile" audio gear, which is just as absurd in the opposite direction.

That's part of why I'm fixing the old HP 654A that triggered this thread - because it was built to be fixed, and to work and last a good long time. I could buy some new Chinese-crap-factory test oscillator for less than the time to fix the HP is going to cost me, but I don't wanna.

(Sorry to offend any Chinese engineers out there. I'm sure there are companies in China making superb, high-quality, reliable, robust products. Unfortunately, there don't seem to be any USA companies that want to import them.)

Are those HP tantalums bad? You would be surprised how long tantalums last if not abused.

last if

This morning I measured their ESR, and they all seemed fine, though one or two have a bunch of crystallization around the terminals.

Is that the definitive test? Is there a better test? (I suppose I should also measure their capacitance, which I've not yet done.)

-w

In the military world, we treat reliability extremely seriously. We use Tantalum for most of the high C applications.

There is an attempt to cut the price of military electronics by using commercial off the shelf components (COTS), but the reliability is not there. Apart from electrolytics drying out, we have issues with plastic packaged ICs which are hygroscopic, and even the in-built tendency of semiconductors to die after a few year due to diffusion of the metalization through the Silicon, and the migration of the metal across the surface of the die.

In summary, the electrolytics are just one of the components which, for consumer level electronics, tend to die more often than we would like, but believe me, you do not want to incur the cost of going high reliability on your next television.

Cheers,

Bill

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