Question aluminium electrolytic capacitor doubt

[gamerfan]

What happens to aluminum electrolytic capacitors that are left unused for long periods?

 

[mindless1]

How long do you consider a long period?

The oxide layer on the foil starts to degrade, which can result in leakage, causing some degree of additional heat and loss of capacitance. This usually doesn't reach a problematic level until several years have passed.

The layer will reform once power is applied again, but if the leakage is excessive, it can cause the capacitor to rupture, so ideally (not that most people would actually do this) a very low voltage is applied and then ramped up over several hours to reform them.

For practical purposes, if I'm going to deploy a used PSU that's been sitting around unused for years I'll just hook up an old HDD (or I have a load tester but usually don't bother using it), jumper the PS_On signal line to a ground contact on the connector, and let that run a few hours before powering a system, and I'll have opened the PSU, made sure there was no dust buildup, examine the capacitors for bulging, and lube the fan if it has a sleeve bearing.

Then there are lower quality capacitors with an unstable electrolyte, commonly the less expensive chinese brands, will break down and produce gas and vent, but this happens if they are kept in use too, typically at an even faster rate.

Finally there is the longest term issue of the electrolyte drying out, but usually this takes a few decades to cause enough degradation to matter, although the demands of the circuit determine how far out of spec a capacitor can get before it poses a problem.

A good quality PSU will have capacitors over-spec enough that you should expect well over a decade of service life whether powered or not, if it is not used at high temperature or near full rated output, which also heats the capacitors due to their ESR, causing them to create a little heat during normal use, even if in perfect condition. An old rule of thumb was that for every 10C rise in capacitor (not necessarily ambient...) temperature, the lifespan is cut in half. This is only for electrolytic, not any of the solid capacitors which generally do not have nearly as much lifespan reduction within their rated temp range. There are more variables involved, a single post can't address everything.

 

[gamerfan]

in an aluminum electrolytic capacitor manufactured in the early 90s and used and assembled in electronic circuits, how many months or years can this capacitor remain without being energized?

 

[mindless1]

There are too many variables to give you an exact, or even approximate # of years.

I would also consider what role the capacitor has in the circuit, for example the further back you go in time, the less likely the capacitor was used in a switching regulation circuit, which eases the wear on the capacitor, and yet that might have allowed the designer to use a less expensive capacitor. Are we still focusing on (computer?) power supplies or just generalizing about *all* electrolytic capacitors?

I'd also consider the rarity or value of the equipment you intend to power, and what cost it would be to replace the capacitor or entire piece of equipment it is in. Make a cost:risk assessment. Capacitors aren't expensive. There are more choices in capacitors today than ever before, so the market can provide replacement parts to keep things running.

If you want to get more technical, then you power the circuit, or reform the capacitor(s) at lower voltage as I mentioned previously and then power the circuit, and consider the function of the circuit, measure the amount of ripple and temperature of the capacitor, or in certain circuits there might be an analog signal like an audio coupling capacitor and you'd want to know the capacitance for the frequency cutoff, or a timing circuit where again, frequency matters but the latter tends not to use electrolytic caps in *most* cases.

It is usually more practical to just replace a capacitor that old, unless you are restoring something antique and there is value in preserving as many of the original components as possible, and they do test to be functioning within the necessary parameters.

 

[gamerfan]

I have doubts about whether to energize these devices in my case at a time that does not harm the aluminum electrolytic capacitors, electronic devices manufactured in the early 90s.

 

[mindless1]

I have doubts about whether I am helpful, or whether you are helpless.

If you want information specific to particular products then you should have just mentioned those products to begin with, and give us an idea what technical ability you have.

Otherwise, either power up the device(s) or don't, at which point they will either work, or won't, and will either let the magic smoke out, or won't.

If the equipment is valuable, just replace the capacitors. It's low cost and as easy as trying to reverse engineer and measure or reform caps, while you have the equipment open and access to them anyway. If you cannot solder, and then probably you don't have the experience doing measurements either, then what alternative were you looking for?

If someone tells you the equipment will be perfectly fine then it isn't, it was just a shot in the dark. If you prefer, you can take the equipment to an electronics repair shop and voice your concerns and have them make a more educated guess, having the equipment in-hand to test, and being able to replace the capacitors while they're at it.

This is a computer oriented forum and this subforum is about power supplies, so if we were to suppose that you have an early '90s computer that you want to have working for historical or sentimental reasons, then just replace the power supply capacitors or buy a new PSU. I'm sure someone out there makes AT PSU to service this market niche, or it wouldn't be hard to adapt an ATX PSU to power an AT circa '90s system, especially since you already have the old AT PSU so you have the relevant power connectors that you could harvest and transplant to the ATX PSU wires.

It would be easier to just replace the capacitors. Either the equipment is worth it, or it isn't. The cumulative time spent by everyone reading this topic, is worth a lot more than a few capacitors. It's like a black hole, but possibly one where a little bit of info escapes.

 

[winr]

Would probing the old capacitor tell you anything ??
And then a new capacitor with an ohmmeter ??

Only capacitors I used to work with would kill if not discharged


Ricky.

 

[mindless1]

Would probing the old capacitor tell you anything ??
And then a new capacitor with an ohmmeter ??

Only capacitors I used to work with would kill if not discharged


Ricky.

What electrical function measurement are you considering with the action of probing?

You can't get any useful pass/fail determination by trying to measure resistance. There are capacitance and ESR meters, but that is more of an investment for someone into electronics rather than just trying to keep a (single?) piece of old equipment running.

Certainly care should be taken when handling capacitors. Most semi-modern PSU have bleed resistors across the terminals to prevent fatal voltages from remaining when the PSU is unpowered, and also the wide range input ATX PSU will bleed off high side cap charge just powering the 5VSB rail even with nothing using 5VSB, but stay safe, do not assume that.

 

[winr]

Thanks for the info .. was just curious, learn something new every day


Ricky.

 

[gamerfan]

my devices snes, tvs crt, ps2 slim, power supply 5v or 12v my old devices with electrolitic capacitors

 

[mindless1]

That is sufficiently vague enough that I'll again just recommend to replace the capacitors. Genuine (sourced from a trusted electronics supply house) major brand caps of the right specs, can't be worse than what has aged in these devices. If the caps are in a switchmode supply circuit, choose something with very low ESR and 105C temp rating.

 

[gamerfan]

Is the leakage current of an electrolytic capacitor from the 90s very different from a new capacitor? If it stays without power for a long time to prevent failures, is the time interval in the old capacitor shorter?

 

[mindless1]

Yes, the leakage current is different because it is aged and the foil oxide layer has degraded, because it stayed without power for a long time. There is no way to predict the "time interval" as we don't have a time machine to see how current capacitors will be 30 years into the future.

None of your questions seem relevant to any useful goal. Either reform the caps and measure them, or replace them, or just cross your fingers and hope for the best.

This concludes my participation in this topic.

 

[gamerfan]

For used aluminum electrolytic capacitors over 30 years old, is it safe to energize devices that use these capacitors once a year for 1 hour? The storage temperature in my house ranges from 33-35C

I don't know if it was left unused for a long time. I bought the devices, they work normally and I energize them every 7 months, but if I have the possibility of once a year, that's better for me.

 

[gamerfan]

Manufacturers of aluminum electrolytic capacitors recommend energizing these components before 2 years of storage. Why is this recommendation?

Is this recommendation only for new, unused aluminum electrolytic capacitors?

Does this recommendation not apply to used aluminum electrolytic capacitors manufactured in the early 1990s?