Yes, if you can agree on the test conditions.
Unfortunately metal film corrosion will depend heavily on air pollutants especially sulphur compounds
X and Y rated capacitors that are continuously bombarded with over voltage spikes do lose some capacitance.
Eventually they can be -20% after a decade or two of mains duty.
They are designed to absorb the interference spikes by vapourising some metal from the plate/s. This uses up life.
Ordinary duty capacitors should never "arc" internally because you will never expose them to the interference spikes .
They last virtually for ever.
Except when you buy some crap with "AUDIO" plastered all over the labeling. Then you don't know what you're paying for.
Eventually they can be -20% after a decade or two of mains duty.
They are designed to absorb the interference spikes by vapourising some metal from the plate/s. This uses up life.
Ordinary duty capacitors should never "arc" internally because you will never expose them to the interference spikes .
They last virtually for ever.
Except when you buy some crap with "AUDIO" plastered all over the labeling. Then you don't know what you're paying for.
Capacitive mains dropping is about the most exposed application possible. Yours seems to be of good quality and doing its job, sacrificing area with each surge
Anecdotal evidence suggests that better quality X caps last longer, so maybe they burn away less metal per incident?
Incidentally, this is why I always advise people to put an X cap across the mains transfomer primary after the switch, not across the switch contacts as many others advise. Assuming that an audio amp will spend more time switched off than on, this maximises the life of the cap.
Incidentally, this is why I always advise people to put an X cap across the mains transfomer primary after the switch, not across the switch contacts as many others advise. Assuming that an audio amp will spend more time switched off than on, this maximises the life of the cap.
Davids,
that's not the difference between X and Y rated.
X are rated to work in the presence of high voltage high frequency interference while being exposed to semi-permanent 220/240Vac
Y are rated to fail safe in the presence of high voltage high frequency interference while being exposed to semi-permanent 220/240Vac.
It's the fail safe that is important.
Across the mains switch does not affect this, since the switch can be closed or open and the equipment should be designed to still be safe.
It's the capacitive connections to Protective Earth that require the fail safe attribute. Here you must use Y rated capacitors.
that's not the difference between X and Y rated.
X are rated to work in the presence of high voltage high frequency interference while being exposed to semi-permanent 220/240Vac
Y are rated to fail safe in the presence of high voltage high frequency interference while being exposed to semi-permanent 220/240Vac.
It's the fail safe that is important.
Across the mains switch does not affect this, since the switch can be closed or open and the equipment should be designed to still be safe.
It's the capacitive connections to Protective Earth that require the fail safe attribute. Here you must use Y rated capacitors.
No. If you must put a cap across the switch just make it a low value Class X.davidsrb said:
Both are intended to fail safe - go open circuit when overstressed. The main difference is that you are supposed to be able to trust your life to a Y cap, so you can put a Y cap from Live to chassis. Also, Y caps must be small values so there is not too much AC 'leakage' current under normal circumstances.AndrewT said:
You can get smaller X caps. People who know what they are doing will use the right cap value in the right place.
Today I found another example of a 'shrinking' X cap. This was a 0.33uF acting as a dropper for the vacuum display and timer chip for my cooker. The display has been rather dim for a year or two - the cooker is only about 7 years old. The cap had reduced to about 0.1uF. Replacing it fixed the problem, and saved me from spending about £60 on a new control board. How much electronics is thrown away into landfill simply because a mains dropper cap needs replacing?
Today I found another example of a 'shrinking' X cap. This was a 0.33uF acting as a dropper for the vacuum display and timer chip for my cooker. The display has been rather dim for a year or two - the cooker is only about 7 years old. The cap had reduced to about 0.1uF. Replacing it fixed the problem, and saved me from spending about £60 on a new control board. How much electronics is thrown away into landfill simply because a mains dropper cap needs replacing?
Sadly, you will find mains dropper caps widely used in consumer electronics where the entire circuit can be isolated from the user. Cookers, doorbells, heating boilers (what Americans call furnaces?). This saves the cost of a low power mains transformer, but the whole PCB has to be replaced after 5-10 years unless the owner knows how to solder.
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