What determines caps deterioration?

In your opinion, what is the main contributor to capacitor deterioration in amps and power supplies? Age or usage?

Age. From manufacture.

Not my opinion. Actual facts.

Heat over time. The hotter they are the shorter the life.

So…usage then?

Not being used. No voltage then no insulating layer formed by oxidation. Many years though.

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Bruss, how many years do we then talk about? 10? 15? 20?

It’s not so much the life of the cap., it’s the estimated time to go out of spec.
But it’s correct that heat adversely affects cap life, as an e.g. I have a DC filter that I made with caps rated at 2000 hrs at a very high 105’C, the same cap when rated at 20’C (average room ambient) has an estimated life of many tens of thousand hours

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Yes, in a way. Electrolytic caps have a temperature rating, in a Class B amp they would last longer than in a Class A one - all else being equal of course.

They deteriorate regardless though but will last longer if they stay well within their rated temperature.

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I don’t know what causes capacitors to deteriorate (over the years I have heard heat, temperature change, rapid heating and cooling, quality of original parts), but I do know that they go off over time, and that nothing can be done about this. So I shall plump for ‘use’, and say that you can’t alter this.

Naim are more vociferous than any other manufacturers than I have ever come across in urging customers to refresh capacities regularly (ideally, every ten years?).

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It depends on whether they are cheap caps or well made ones. Naim recommend a service interval which I hope is based on their experience. I have 35 year old kit that still sounds good, but then I have seen newer kit with blown caps. Better to replace too soon rather than too late.

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The answer to this question is quite complex.
There are a number of degradation mechaisms at play. The main one is chemical then there is also one of drying out ( not quite that simple, but best to think of it like that). But these mechanisms are accelerated by temperature. So yes, caps degrade from day one, used or unused. If used and kept cool they still degrade but more slowly.
Change out is the only recommended maintenence strategy, not least as the OEM can simply sell you some more. Testing them is possible, but requires removal from the board, hence you could test and refit, but…
In extreme circumstances i have seen large caps explode and deposit themselves inside a cubicle. Not pretty. These were large caps that were on the DC link of an inverter. The inverter drive was swapped out. Caps were the size of a large beer can.

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When I’ve seen videos of people fixing broken electronic stuff, if it’s the caps, then it tends to be the larger ones. Does anyone know if that is typical, or just my incorrect view of the repairs?

I find the phrase ‘explosion in a cubicle’ terrifying. It brings to mind pictures of being stuck in the middle of Euston Station when the toilet block lets go. Talk about being caught with one’s pants down - or, as a good friend would have it, caught avec les pantalons en bas!


I expect if i’d have been stood next to said ( electrical) cubicle the results could have been similar.

My great great grandad always said never to put your cap away wet :smile:

Similar experience here, having seen the results of exploded caps in inverter (variable frequency) drives. Drive doors are fitted with interlock switches and bolted shut around the perimeter because of the potential damage an exploding cap can cause. You would not want to be standing in front of an open door when one goes, or even in front of a closed door that wasn’t bolted down.

The life of a capacitor quoted by a manufacturer is based on the capacitor voltage rating and temperature rating.

IE. 10,000 hours at 40v/85c

At 40v/30c it will last a lot longer. At 20v/30c it will last even longer.

If you look at an olive nac72, it is littered with maroon roedersein capacitors having a rating of 40v. Some are working at 24v, some are working at a couple of volts. The ones working at a couple of volts (feedback caps) will last a very long time.

So, a capacitor used at max voltage and max temperature rating will succumb to usage. A capacitor used at 5% voltage rating and 5% temperature rating will probably succumb to old age.

Whilst temperature x time are major factors, there is no and hard and fast rule regarding how long capacitors last, and it doubtless depends on the capacitor’s specific design, construction and operating conditions. I sent a Musical Fidelity P270 for service at about 25 years old, thinking it was probably high time it was re-capped, especially as it is a very hot-running amp due to strong bias into class A (internal air temperature about 60C when I checked once). Whilst they did indeed replace some caps, that, interestingly, did not include the reservoir caps, which apparently were found to be still satisfactory and within spec.

So one that’s not used at all will be good for how long?

Not predictable as it would depend on the design & construction,mand storage conditions - you’d have to consult the manufacturer…

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