I must stop replying to myself... I spotted an interesting thing in the datasheet - the lifespan of this part is 12000 hours - which isn't an awful lot.
Assuming it's on for six hours a day, that's less than six years.
Regards,
Steve
That'll be specced at maximum operating temp. In any more normal application you can expect vastly more than that.
d
Interesting! I checked a few manufacturers and 12000 hours seems towards the top of the specifications, some specifying a lot lower. This got me thinking about broadcast equipment which is usually put into service and left powered up until it is taken out of service perhaps 15-25 years later. This is particularly so with transmission equipment which is normally expected to have a 25 year life.
One year has 8760 hours, so stuff left on for 20 years will be operating for
175,000 hours. I have equipment at home that's been on for well in excess of 50,000 hours (standby operation still has the power supply on) so I wonder what the 12,000 hours actually refers to.S.
As I pointed out elsewhere, that's at the maximum temperature, and derating appears roughly exponential. At 30 degrees C less than its rated temperature, which is not unreasonable, it might last five to ten times that.
I don't think 12000 hours is bad for an electrolytic. The old rule of thumb was seven years, though of course many go far beyond that. A bit like hard drives.
Farnell have a few 15000uF that come close to your spec:
e.g.
I've got an AR88D with some electrolytics coming up for their 70th rather than 7th birthday :-).
Where do you get the 7 year rule from, and what exactly is it? I've never come across it, and if it existed I really ought to know.
I've still got 1930s lytics in service, and IME lytics are a long way down the list of most likely failures in old equipment. The ida that lytics have short lives seems to be an offshoot of the spate of bad caps on mobos in the 90s.
NT
In message , snipped-for-privacy@care2.com writes
The failure of electrolytics over time is due to the drying out of the electrolyte. The capacitor will generally read the correct value on a capacitance meter but will develop a high ESR (Equivalent series Resistance) which causes ripple on a supposedly smooth DC supply. (And timing problems in old circuitry.)
When your old TV starts to hum and there is a dark ripple across the screen or the picture tears away at the corner.... That's a dying electrolytic.
I missed the start of this thread. Is the subwoofer humming even when the audio source is disconnected?
Well I had to fix an old valve radio that was late 50's vintage..that had packed in its electrolytics after about 40 years.
Lost of valve stuff has that as the single and only real fault.
well it hums only when the *mains* IS connected..and on..
In message , The Natural Philosopher writes
If it's just the mains and no signal then it sounds like either the PSU capacitor as suggested or maybe just sloppy circuitry picking up hum. Maybe even bad placement of cables inside if it's an active unit.
Exactly. When I was a teenager (can't remember when that was, but a while ago), I'd fix old valve radios for relatives, friends, neighbours and assorted hangers on.
The most common fault by far was a failed smoothing capacitor leading to a hum. I had a box of assorted diameter ones that would fit the clip on the chassis. It didn't particularly matter if they were larger capacitance than the original.
The second was that they had left the radio tuned to one station for donkeys years (normally the Light Programme or Home Service) and now wanted to tune to something else. Of course, the tuning capacitor would be crudded up and would cause crackles or have intermittent contact requiring "mechanical treatment" of the set. A quick go with the vacuum cleaner and a squirt of contact cleaner usually fixed these.
The third, but fortunately extremely rare one was a failed selenium rectifier. When these are on their way out, they emit the most evil of smells known to man and having a strong emetic effect.
Any of these repairs would bring forth a nice afternoon tea plus an amount of folding that was way in excess of the time and materials cost of the repair.
Regarding electrolytics in these old pieces of equipment, the failure mode was pretty obvious - I took several apart for curiosity. Inside they would be packed with some kind of gunk soaking the dielectric. On working ones this would be quite gooey. On failed ones it had hardened and become cracked. The hum wouldn't suddenly appear but would get worse over the years until it was noticably bad in comparison with something else like the TV.
It seems no-one can backup this 7 yr rule so far. Its far removed from my experience with lytics, and lord knows I've worked with enough of them. IME around 4 out of 5 1930s ones have still worked, so thats a mttf of ballpark 70 x 4 = 280 yrs.
I'm surprised by Andy's experience, I've also fixed lots of valve kit, and lytic failures have happpened but been fairly rare.
If there had been any sort of 7 yr rule, a lot of the new kit I've worked on would never have got out the door, as 7 yr life would have been unacceptably short.
NT
Bear in mind that the lifetime of electrolytics will follow some kind of normal distribution curve, and the quoted seven years will represent the very start of the lower end of the tail - probably 0.1% of the entire distribution, maybe even less. So the average life is probably more like twenty or thirty years, with the upper tail extending possibly to a hundred or so.
d
Certainly when called upon to fix the valve radio, I did a lot of web research, and it was, with selenium rectifiers, the largest single problem.
Ageing coils needing tweaking and ageing valves were most of the others.
resistors rarely go, and in modern kit semiconductors are nearly as good.
Dry joints in PCB's are the final big failure mode.
If that is so, then equipment with 100+ caps in would see higher failures than they really do IRL. Milspec equipment is very reliable. Or do you mean 0.1% of equipment with lytics in?
I'm still trying to marry the 2 somehow... It doesnt strike me as very likely that I would have worked on such an unrepresentative sample. OTOH on the web I've seen lots of individuals and sites spring up (all since the bad cap mobo issue) that say lytics are the problem. Does that mean they really are though? I dont think it does.
But I still dont see how to take account of both Andy's experiences and mine.
NT
Rotten fish - very nasty.
Old resistors rarely fail, but the old carbon ones do drift up in value pretty consistently over time.
I once repaired a tape recorder which had failed after about twenty years. The fault turned out to be a wire on the mains transformer which had been bent round the tag and not soldered at all - it finally oxidized enough to lose contact.
d
Just don't let them get too hot - that was always the rule that guaranteed long life for electrolytics.
d
Valve amps get hot, and old electrolytics are mot made as well as modern ones.
They all dry out..also paper caps..
Its unusual for modern caps to go..BUT the high ripple currents in big smoothers make em warm..they dry out faster.
ALL mil spec kit I worked on used tantalum electrolytics too..not a hint of an aluminium one.
It has always been know that Al electros were a weak point..temperature, tolerance and failure wise.
However, stick al electros at low power in a place where a high AC impedance won't cause a particularly huge effect..and they will soldier on for years and years.
A modern power amp is likely to be DC coupled throughout: Or have one or two non electrolytics in it for the purposes of rolling the extreme bass off....the only electrolytics will be the supply reservoirs..other than going to an SMPS there is no way to avoid those and SMPS add their own problems ..400v capacitors being need anyway to smooth the incoming mains.
What puzzles me is that the common mode rejection is not better on the amp..it should be able to cope with quire a lot of supply ripple. But its certainly the firts place I would look..connections to the reservoirs.
I hope they've got better. When they first came out in the '70s, the BBC made extensive use of them. And one series of sound mixing desk had to have them all replaced at about 2 years old. Thousands of them. ;-)
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