Re: 2465B power supply - Sprague 290uF/200V big blue caps


Where did you see the mention "near rated voltage"? It plainly says:

"In electrolytic capacitors, applying DC voltage actually drives a beneficial, on-going electrochemical reaction that heals defects in the anode dielectric."

Followed shortly by a description of the negative effects of simultaneously maxing out on both voltage and current/temperature.

---In TekScopes@..., <david_wise@...> wrote :

I read CDE_Multipliers.pdf, and they do claim that operating near rated voltage has the beneficial effect of repairing weak spots in the dielectric. Their graph of voltage life multipliers also stops at half of rated voltage.

I don't know how strongly this correlates with the useful life of a cap operated below rating. I suppose a graph would show a sweet spot with maximum life, with less at each end. I can't begin to guess at the shape of the tails.

The Shelf Life rating is based on storage at rated temperature. We don't know the degree to which thinning is accelerated by heat, although Arrhenius would be a reasonable first guess. A cap stored at comfortable room temperature will last much longer than the rating.

The Shelf Life test also applies rated voltage after storage. If the circuit applies only low voltage, this test will reject caps that operate just fine.

I just can't get righteous over this, but certainly there is *some* effect. We just don't know how much, and the people who research this for a living don't care about this operating point. I'm determined not to lose sleep over it.

Dave Wise

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