One of my ongoing hobbies is the autopsy of failed domestic appliances. We live in the land of 240VAC domestic supply. LED ceiling lamps fail with regularity. So far nine in the last five years and all with the same fault… the 4.7µF 350V 85°C Electro. after the bridge rectifier in the SMPS mounted in the base of the lamp.
Where else would you mount a small electrolytic running at maximum voltage, in an enclosed area, except, just above a bank of heat generating LEDs???
Maybe I should screw them into the floor?
I think of it as planned obsolescence.
Back in my more youthful days I earned a lot of “pocket money” repairing CRT TVs outside working hours.
Aside from dry joints, the most common failings were the small electros., especially the ones mounted near the heatsinks in the SMPS and Horizontal Output stages. The switching transistors may have failed, but the Electros. were, in most cases, the culprits for those failures.
Yes. Even though I design switching power supplies, I have been surprised that the HV switching MOSFETs rarely seem to fail, even though they represent the greatest amount of electronic “action” within the power supply. It is the small aluminum electrolytics.
On the subject of LED lighting, I do not have so may yet as I have not yet burned through all of my CFLs. The difference in efficiency is not large enough to warrant discarding good working CFLs. I have heard of failure prone LED lamps but I have not experienced it. From what you are saying, I suspect that we may be better off here with 120 VAC. When you look at available aluminum electrolytics, 500 (or maybe 600) VDC seems to be some sort of technology limit. The ESR gets much worse as the voltage rating goes up. I do not know whether our LED lamps have electrolytic capacitors inside, but ours would not need to be rated more than 200 or 250 VDC. In our kitchen, I installed dimmable LED tubes which physically replace 120V 60 Hz fluorescents but with the ballasts removed. I am very much a dim wit when it comes to lighting.
Having repaired many LED lights on my 240V+ AC in a hot climate, it’s the output capacitor that fails most often. I note that most capacitors used claim 105C rating.
Back to the OP
Plastic film capacitors only seem to fail in a human lifetime for one of three reasons:
exposure to excess voltage ie surge on mains inputs
handling/soldering damage spoiling the package seal - get your lead pitch correct
poor choice of oil in the filled types - some “audiophile” types use cooking oil!
Another failure mode is “manufacturing defects”.
In the first 20 minutes from the video below, Dave is yapping around in his own brainless style, but in the last 10 minutes he’s calling in some help from a capacitor god and it becomes really interesting.
And about LED ligting…
Those things should not get hot at all. A lot of the LED’s that get hot are also overdriven. By reducing the LED current, not only the heat goes down, but the efficiency of the LED also goes up. LED lighting can have an efficacy of 200lm/Watt these days (some interesting video’s on youtube on “Dubai LED’s”)
The form factor of the old light bulbs is also a gross mismatch in form factor for LED’s. First, LED’s like a low voltage DC, and second, if the LED is separated from the electronics, the electronics is much easier to keep cool too, which prolongs their life time. I’ve bought a bunch of 12V COB led panels on a 35x120mm alu plate which are supposed to be 10Watt. They stay quite cool upto about 6W, but above that they “suddenly” get quite hot.
And best I know, electrolytic capacitors are by far the worst electronic component that is in wide use these days and they have a short life time ( Often as low as a few thousand hours, but it’s prolonged by de-rating) Apart from those capacitors (nearly?) all other types have a “near infinite” lifetime.
Not only Dubai Lamps, but today there are 210lm/w LED lamps available for Europe / EU, and I think the same guy who took apart the Dubai lamp also took apart those EU lamps, and found out they have a different driver circuit in them.
I assume that the video I just watched was the same one…Very interesting stuff. He did note at the end that the Dubai lamps are not dimmable. I would think that dimming an LED lamp would allow it to last longer. I am sure there is some truth to that, but dimming (with a typical thyristor based dimming circuit) and increasing the number of lamps to get more light might not work as well as better derating in the design.
I put a (call it a bright “night light”) in our laundry room. It is powered through a small wall plug power supply which may be left over from a cordless phone set. It has four 1W LEDs, each running at about 45 mW. This is plenty of light to see one’s way around the laundry room.
For audio applications, ceramic caps create quite measurable high-order harmonic distortion. Film caps will give a smoother sound. Any FFT will show this. The best option for Moog circuits is probably more modern, low-noise opamps. It’s pretty subjective at this point since a synthesizer is basically a noise/harmonic generator in its basic form.
