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Recapping power supplies: Type of electrolytic used?

Most use plain old aluminum "wet" electrolytics. Assuming they're not abused, they'll give you at least 10 good years of service. Solid polymers would be preferable, but the extra cost generally doesn't justify the application.
 
Also, in a power supply, it's not a good idea to use different types unless you really, really know what you are doing. The characteristics of the whole circuitry may change if you use different types of caps, and that's not good especially on the primary side with mains voltage.
 
A bit more about this - in high frequency switching power circuits electrolytics need to be specifically ones with low ESR, at least in the high frequency portions of the circuit, which usually means all of the ones on the low voltage output side. If you replace them with run of the mill electrolytics the refurbishment will have a very short and unsatisfactory life. The high voltage caps on the mains side of an SMPSU will normally be dealing with 100Hz or 120Hz ripple, so they are the exception and do not need to be low-ESR parts. You should however use ones rated at 105 degrees, as with all the rest.

Timo makes a good point about how sometimes replacing an original electrolytic with a new one may actually adversely affect operation of the circuit if the characteristics of the new part are too different to those of the original part.

My suggestions for anyone thinking of recapping something, whether it is a computer or anything else, are:-

Do you really, really need to do it? If it isn't broken, don't fix it.

If you do feel there are valid reasons to recap - maybe some are visibly distressed or the unit / item is exhibiting behaviour synonymous with bad capacitors, then:-

Before removing any capacitor make sure the polarity marked on the PCB matches the polarity indicated on the capacitor. In some rare cases the screen printing is incorrect, but the capacitor has been inserted with correct polarity. If you find one of these put the new part in the same way the old one was oriented and not as indicated by the screen printing.

Whenever you take one capacitor out either write its original component position / circuit diagram part number on it or put it in a small ziplock bag or component tray compartment and write its component number - the circuit position from which it came - on the bag or tray. This is so that if your PSU or whatever does not work after recapping, you can return the original parts to the positions they came from one by one until it starts working again.

Make a point of taking out and replacing only one capacitor at a time, to lessen the risk of getting into a situation where you don't know which of two or more places two or more capacitors came from, especially if you don't have a schematic for the item in question.
 
In almost all cases polymer or hybrid polymer can be used in place of wet aluminum electrolytic. Generally lower ESR than the wet cousins--and much longer service life. Downsides: somewhat higher leakage current and more expensive and not available in higher working voltage ratings.

A brief guide.

Again, given that most wet aluminum electrolytics have a design lifetime of 10 years, is there a significant benefit toward using something better, but more expensive?
 
Well, let me tell you a story. Back in the 1990s we won a contract to look after some city centre CCTV systems, and at the heart of those systems were a certain type of video multiplexer. These were all rack mounted in cabinets with glass doors, a recipe for disaster, surely enough, they started to fail a lot. The manufacturers wouldn't let us have replacement SMPSUs, they always insisted on having the whole thing back and taking ages to fix it, so there came a point where one went down, we had no spares at the time and the user desperately needed this unit to be working.

So we took it back to the workshop, took the SMPSU apart and noticed that some of the electrolytics looked visually suspect, so, as we kept a large stock of ordinary electrolytic capacitors, we recapped it, observing value, voltage and polarity of course, and to our delight it sprang to life. Took it back, installed it, customer happy. Until, that is, the same unit failed several months later.

This time we had a spare so we swapped that in and brought the original repaired unit back to the workshop and were mystified to find that most of our months-old capacitors were showing obvious signs of distress. Bulged, leaking.

At the time the now well known phenomenon of 'bad caps' wasn't really a thing so we thought an electrolytic was 'an electrolytic'. The fact is, though, that the capacitors used in SMPSUs are run at ripple frequencies up in the high KHz range and therefore have to be specified to work at those frequencies whereas 'ordinary' electrolytics are only expected to deal with mains ripple or audio frequencies.

If you use run of the mill electrolytics to re-cap an SMPSU it may work, but not for very long, and certainly not for anything like ten years of continuous operation.
 
Heating due to ripple currents is mainly due to a too-high ESR, which will eventually kill an electrolytic.

Generally speaking, low-ESR caps will work even in SMPSU applications. If you have serious doubts, use a nonpolar device. If you're seriously into reliability, use a power film capacitor.
 
I'm not sure if you meant to say "Low ESR caps will work even in non-SMPSU applications". Certainly low-ESR, high temp (105 degree) types are the only type I would put in an SMPSU these days.
 
Both ways--buying cheap high-ESR caps nowadays is a fool's errand. Since 1995 or so, capacitors have gotten a lot better, though I still wish that I could find motor start capacitors made with PCBs (e.g. GE Pyranol). Modern start/run capacitors have ridiculously short lifetimes.
 
in my last recap (my old datability terminal server), i used Panasonic FM-A series, low ESR, specified at 105 C and 7000 hours, hope they would last long.
 
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