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Capacitor voltage ratings

It depends what you mean by "long term"... Generally it's safe to run at the max rating.
If looking for 10 year plus reliability then best to derate rather.
Obviously don't leave gear on 24/7 if long life required!
 
If you search hard enough, you'll find life curves for very many capacitors, including ones at volts varied away from rated.

Effects of increasing applied voltage also varies by type/construction method.

I used to work in tantalum cap' R&D and the insulator/dielectric, which is tantalum pentoxide, is formed electrolytically, in the ones that I worked on, at around twice rated volts, so they would go short-circuit at around double rated volts. Between rated and forming volts, they get progressively more leaky (higher leakage current - Li).

Failure mechanism in things like film cap's is going to be way different, but no doubt discussed online in many and various places.

I have no idea if they are now or ever were available generally, but some grades were aged using Weibull aging, which can produce cap's with truly massively extended rated life as the principle allows early failures to be eliminated from any one batch, so average expected/rated life of the remainder is increased. Too complicated to go into here, but again, no doubt, lots online if intrigued.

With any cap' with an immobile, non-volatile electrolyte, potential life is limitless. The common quote that "they dry out" applies to some but by no means all cap' designs. It does not apply to electrolytic tantalums as there is nothing in them to "dry out", they are 100% solid state, indeed, moisture ingress just makes them electrically leaky to some degree.
 
I'm assuming the OP means electrolytics but we could do with more info on that!

If tantalum then it's not even safe to operate them at their rated voltage!
 
Arkless Electronics said:
………...If tantalum then it's not even safe to operate them at their rated voltage!
Click to expand...

Strange indeed then, that they are regarded as the "Rolls-Royce" of capacitors by the electronics industry.

The ambition of the manager of the major project that I worked on was to be able to claim "Inside Intel", as the goal was to make them small enough to embed within a processor chip. Hardly likely if they are so unreliable.

Electrolytic tantalums are tiny, low ESR, much better maintenance of properties with increasing frequency and low leakage for any given rating, compared to the competition. Need cheap and cheerful by the ton, not too fussed about ESR in particular - use ceramics.
 
Some types of tantalum caps are very reliable but most of the bead types are not and their fault mode is often direct short circuit which can be quite detrimental to other components such as regulators where a sudden short circuit on the input puts reverse volts across the reg with obvious results.
 
One point I picked up from XRayTonyB’s YouTube channel which made a lot of sense to me is over-rating the voltage of electrolytic caps when replacing (i.e. replacing with a higher value) isn’t necessary a good thing long-term as the circuit lacks the voltage to reform them, so over time they sag/age prematurely. He knows what he’s on about as he is a XRay service tech with a hobby/side business restoring vintage audio kit. His view is to replace like for like as much as is possible unless the schematic suggests the original spec was inadequate. I’m pretty sure I’ve heard similar on Mr Carlson’s Lab and Blueglow Electronics, all of whom I’d trust.

PS There really is a wealth of amazing geeky stuff on YouTube these days! I watch hour after hour of it!
 
Vinny said:
Strange indeed then, that they are regarded as the "Rolls-Royce" of capacitors by the electronics industry.

The ambition of the manager of the major project that I worked on was to be able to claim "Inside Intel", as the goal was to make them small enough to embed within a processor chip. Hardly likely if they are so unreliable.

Electrolytic tantalums are tiny, low ESR, much better maintenance of properties with increasing frequency and low leakage for any given rating, compared to the competition. Need cheap and cheerful by the ton, not too fussed about ESR in particular - use ceramics.
Click to expand...

I would basically say the opposite of everything you say!

They always blow short circuit for a start and some even have/had built in fuses to try and avoid damage when they go.
USA Mil spec calls for tants to never be used at anything over half their voltage rating.

Poor for audio as well as they generate distortion.
 
Thanks guys. Yes electrolytics. I am thinking of trying a ripple eater supply in some power amps. The supply when loaded with a pair of resistor to simulate the amps current draw is outputting +- 34.2 to 34.7 vdc with caps on the amp boards being 35V ones I felt a bit concerned.
 
At Marconi I used to have to put a 2R2 resistor in series with every tantalum decoupling capacitor, rather defeated the purpose.
The bead ones really do fail a lot. At RACAL we had to fit glass beads on the leads. The theory was that the epoxy seal had to be kept away from the solder joint
 
davidsrsb said:
At Marconi I used to have to put a 2R2 resistor in series with every tantalum decoupling capacitor, rather defeated the purpose.
The bead ones really do fail a lot. At RACAL we had to fit glass beads on the leads. The theory was that the epoxy seal had to be kept away from the solder joint
Click to expand...
I didn't know you worked at Racal. I have a RACAL DANA frequency counter and it's a lovely instrument. Chapeau!
 
AFAIK electrolytics are tested to 1.5x rated working voltage but can't find info on this at the moment. My NCC200 uses 25V transformers which give 38.5Vdc per rail off-load and I used 40V Philips BC caps in the PSU. 10yrs old and well over 3000hrs use with no problems. Watch it blow up at the weekend now I've said that!
AP
 
Only get occasional dimming when they switch supply circuits. Other than that not seen anything unusual. Maybe luck then.
 
I've had beyond expected lifetime use from small caps used 10% over rated voltage. 16v nichicon fine gold.
 
And I've seen 'long life' Kemet/BHC 40v caps die by drying out completely when run at their rated voltage (Naim XPS I'm looking at you).
 
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