EEVblog 1486 - What you DIDN'T KNOW About Film Capacitor FAILURES!
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- Опубликовано: 2 авг 2024
- You might think you know how film capacitors fail and degrade in capacitance over time - self-healing due to surges, right? WRONG!
Capacitor expert and AVX Fellow Ron Demcko confirms what's really going on after a teardown of some failed and one good polypropylene X class capacitor.
00:00 - Teardown of a some failed film capacitors
00:52 - Self Healing and drop in capacitance
01:44 - Capacitance Measurements
02:15 - Teardown of a new Suntan brand polypropylene X2 film capacitor
03:03 - Different failure modes based on size and winding pressure
05:52 - Unwrapping the film
07:51 - The film inside a NEW film capacitor
09:19 - Teardown of the FAILED uTx brand heater capacitor with half capacitance
10:06 - How Schoopage and the end pin terminations work
12:23 - Teardown continues...
12:45 - WOW! What on earth is this?
14:54 - Elecami Wolf also did a teardown
16:05 - Teardown continues...
17:01 - Separating the film showing both slef-healing and extensive metal film corrosion
18:29 - Another uTx brand failed film capacitor from a Corsair PSU, with 90% loss in capacitance!
Elecami Wolf RUclips Channel: / elecamiwolf
19:55 - Let's call an expert! Ron Demcko from AVX tells us the REAL REASON for the failure!
It's moisture ingress and corona demetallization!
Full discussion with Ron Demcko:
• Full Discussion - Film...
Metallized Film Capacitor Lifetime Evaluation and Failure Mode Analysis report:
cds.cern.ch/record/2038610/fi...
Film Capacitors construction: passive-components.eu/capacit...
Film Capacitors self-healing explanation: passive-components.eu/capacit...
Film Capacitor types: passive-components.eu/film-an...
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#ElectronicsCreators #Capacitors #Teardown 
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Comments from Dr. Tomas Zednicek founder of European Passives Component Institute, and former AVX:
Quote:
I did look at the whole video - congratulation to your teardown skills 😊. Regarding the phenomenon you observed - I see two/three potential issues on the failed cap:
1] uneven metallization. If you look though the unwind foil of the fail cap vs the reference one it looks that the centre section of the failed one looks lighter compare to the edges, this might indicate that this area is thinner compare to the edges. This does not have to be a manufacturing error but even an intension. You mentioned shoopage reinforcement (also in ref here on my web). The target is not only to make the connection more mechanically robust, but make lower ESR and improve performance on the pulse load. You can image this as an “skin effect” at pulse - high freq spike load - the most exposed area is the one closest to the termination lead - and that has to have a lower ESR - achieved by the edge thicker metallization/shoopage reinfforcement. If you go towards the inner side of the cap - centre of the foil width (if you looked at unwind foil), the resistance increase with the length path and thus the pulse will not expose that area. So actually you do not need uniform metallization thickness across the whole foil width, thinner metallization at the inner side is supporting better self-healing for longer life time and thicker metallization at the edge increase pulse robustness. This is a reason why you see defects in the centre of the foil where self-healing / delamination happens first. This type of failure mode suggest that the cause may not be originated by pulse overloading (in that case you would see a burn spot on the edge - as you expected) - but there is a degradation of the foil under a regular (non-spiked) applied voltage. If the metallization layer is thinner (as a manufacturing fault) or improperly designed you may see such type of failures.
2] moisture degradation. Quality of film caps may be also strongly impacted by quality of the encapsulation resin. Indeed - this class of commercial caps are non-hermetic - but cheap and poor epoxy resins used for encapsulation may not protect so well the capacitor core element and even capture some moisture with time. The metallization may be sensitive to moisture and if there is a higher humidity inside it speeds up its degradation processes. As per the dark spot areas on the metalization of the failed capacitors I could guess that some level of degradation present and I would point moisture on the top of likely the cause. Also presence of “lightning like” spark line at the centre of the foil suggests that there may present a moisture / conduction path causing the defects.
3] combination of 1] and 2]
As often seen on the market I would guess 2] may be the root cause of the failure in this case, low cost unbranded capacitors often use inferior cheap epoxy resins that are sensitive to moisture and longer term it degrades capacitor performance. You can check this easily by testing of moisture robustness of these capacitors capacitance drop at humidity test (even after 500h 40C/90% you may notice differences and even shorter if you would apply 85C/85% load). The conclusion here may be to use safety capacitors from brand manufacturers with trust if you really care about safety.
Thank you very much for all your videos you are one of those big help on the internet which thousands really appreciate so thank you once again for all your vidoes and hard work. Are these dc capacitors or ac? can you measure their capacitance by dc meter??
'this call will be recorded for quality purposes' , regretted the bank now storing an hour-long copy of Dave talking about film caps 😆
Recording doesn’t occur during the hold; it is started when the representative gets on the line.
@@stevebabiak6997 Kinda sad, they could learn so much. ;-)
@@strenter please for the love of god don't give any other ideas...
Shooting a video while on hold on phone is lowkey genius
I was on hold for 30+ minutes with (IIRC) my gas supplier a few months ago. I missed the call, because I fell asleep while waiting and listening to that bloody elevator music... I actually recorded it for myself, the women hung up after less than 3, maybe less than 2 seconds after I haven't responded. Haven't even tried to wake me up xD .
Why?
For anyone wanting to unwrap a cap themselves. If you shave the ends of the roll flat and clean with a razor/scalpel, you can usually get the film off without much (or any) tearing.
I had this discussion about 5 years ago with James Lewis formerly of KEMET when I saw this note in the data sheet about NOT using X2 capacitors for dropping supplies. He reiterated that moisture would cause corrosion in as little as a year because of sealing and moisture. Cost was a major issue and these capacitors were designed to last long enough to get thru EMI testing. Long life was never to be expected. At the time they were thinking about a line of X2 capacitors which would actually bd designed for dropping applications. Bottom line was to avoid using X2 capacitors, yet many designers insist on using them in designs vs other film capacitors. Lewis had left the company at this time. Perhaps your guy was hesitant to say that these capacitors were designed to fail.
Kemet, home of the smoke bomb... Did he have anything to say about paper capacitors in particular? Anyway, glad to hear Kemet was also thinking about dedicated dropper capacitors. Vishay and Epcos actually realised such types. Maybe Kemet as well in the meantime?
X2 capacitors in general have already been safety agency approved for use on AC mains; other capacitor types in general do not have such approvals. It’s much easier to spec in a safety agency approved device when AC mains are involved, whether that device will perform the best or not.
@@mjouwbuis Paper capacitors predate Kemet buying that factory by decades. I've seen paper capacitors from before 1950, using primitive resins for sealing, and those devices still worked!
Those capacitors were made to be SOLD, not necessarily to be USED. It's great to hear the perspective of a practicing professional engineer (with all due respect to our enthusiastic host).
The most important difference is that the more expensive brands such as Epcos and Vishay, explicitly mention that normal X2 capacitors are unsuitable for use as series droppers.
Well it's not just a practicing professional engineer, it's a specialist with 40 years experience with capacitors in particular.
"Moisture ingress" into a device enveloped with epoxy, after only a year!!!??? You're right - these parts are mere facsimiles, not actual electronic parts.
@@mjouwbuis Panasonic, though, state in their ECQUA (PP X2) datasheet (at least an older version, the current revision doesn't say specifically) that it *is* suitable for series dropping, and don't make a separate series (unless you count ECQUB which is for X1 class, and also Y2 in low values).
Along with Okaya, they seem to be the most reliable (at least from my limited sample, but each piece I've tested so far from those two makes remains within tolerance).
Purpose-made high-stability types may well be preferable for droppers, but when capacitors degrade to
This video and chat with Ron needs way more upvotes. Digging into the manufacture and failure tests of components would be a staple of an Engineers TV Channel.
thx always nice to have a person with a PhD in upvotes/downvotes (aka. likes) giving a diagnose about what other people should thumb and to what extent.
Back in the 70s, Sprague came out with "Orange Drop" film capacitors which were hermetically sealed in orange epoxy (powder dipped in an air bed and then baked to activate the epoxy powder). They became extremely popular, because they eliminated the eventual failure of the paper / wax capacitors used in everything. They were mostly Radial for PCBs, but every now and then, someone would bend the leads straight at the body juncture to make them Axial. This would crack and remove the epoxy on the leads at the body and let humidity leak inside over time, eventually causing a value change / failure. All of the other film capacitor manufacturers adapted this outer case sealing (powder coated epoxy) as soon as they could figure a way around Sprague's Trademark/patent. Turns out it was simple: any color but orange!
GE made these by molding white nylon over them (since this was a GE Plastics product), but alas, it did not prevent moisture from getting in and they would self-identify by become a bloated barrel shape. Ah yes, the good old days 😁
@Banter Maestro2 Yep. GE plastics thought they found a new market, GE Electrical Components lost one.
The orange drop capacitor was very popular for use in CRT horizontal deflection circuits; IMO they would be a good candidate for use in the application that is the topic of this video.
And the orange drop was a metal film capacitor, and not a metallized film capacitor; the metal layer was thicker to be able to support higher currents.
Vishay make modern copies of the Sprague orange dip. Pricey little tators.
Nylon can absorb 4% of its weight in moisture @@shazam6274 not a good choice of plastic!
This was *super* interesting, thanks! I'd love to see a series of videos looking at how other components are constructed and what happens when they fail in a similar level of detail, and talking to a similarly-knowledgeable expert about anything unexpected as you did here. Great, great video!
This is not a failed cap. Its a capacitive surge counter with a fail safe condition.
I know that they call this feature "self healing", but that would imply that the capacitor can continue to absorb voltage surges and keep performing properly, when It does not. They should rename it to something like "safe degradation" , which would at least be truthful.
Oh, such memories! At one time I was involved in various capacitor reliability issues. Then the things proceeded to building AC high voltage capacitor winding machines. Further an idea about why not making smaller capacitors and a winding machine for those (just one machine as the product was abandoned). We did not have self healing materials, we tried just aluminum film and various polymer films. What we tried to make was high discharge rate special capacitors. For that goal, we also tried the offset aluminum films and metallized ends. Tried tin spray and zinc spray. Well, I moved to other tasks before all those endeavors were finished. The main business was cable manufacturing. Our department built the machines and control systems. So, when we wanted to make high voltage cables -- basically big coaxial ones -- there was a question about corona between the inner and outer conductor and the insulation. That was solved by extruding 3 layers, thin conductive plastic next to each metal and actual insulator between them. But then we found there still were something called partial discharge phenomena. The traditional testing had been with line frequency AC, but in this case it turned out to be impractical for various reasons. Our department together with the high voltage test department built a testing system using single sine pulses with a low repetition rate. While that project continued, I got transferred to an entirely different division to tackle new problems at a brand new R&D department. But something stuck in my memory about capacitors, corona and especially the partial discharge issue. Ron Demcko probably knew all of those details as well, although did not want to go to potential trade secrets.
Partial discharge would produce ozone, just like corona. So it’s just as bad of a problem.
Thanks for the tear down and expert opinion collaborator. If I’m serious about a design I’ll go with a seasoned experienced parts manufacture. It’s like coding, garbage in, garbage out. 🎈
Great one Dave👍
I have several cheap RF remote AC outlets. They all use capacitive dropper power supply. The dropper caps are typically only 200VDC rated. They drop in capacitance until they can no longer power the relay. I have replaced them all with caps rated 400V to 630V. None of those have failed.
None of those have failed *YET* .
There, I fixed it for you. They will all fail, that's the nature of the design.
200vDC is rather inadequate when mains is +/-340v.
@@liam3284 170V here in USA. But with transients etc. it's still inadequate. They cheaped out!
@@johncoops6897 Well it's been almost ten years and the 400 to 630v replacements are all fine. The electrolytic caps will probably fail first...
13:02 honestly, a high-res shot of that film would make for an interesting desktop background 🙂
Cheap X2 caps are definitely worse than good brands. Had big trouble with them at work about 15 years ago, purchasing loved this brand because they were cheap but sales hated the failure rate! However be careful with the peak currents in your circuit during normal operation, especially when using them as decoupling caps for PFCs etc as they can run hot due to their ESR and degrade fast! Especially if the ambient is hot. If you don’t mind spending more, specify a good make of class X1, they are way more robust.
This is the type of content I've always wanted to watch! Not just tear down with a comment from Dave who is repeating that he do not know what are we looking at, but comments from someone who actually built the thing and know exactly what are we looking at.
Very timely video. I have a Solar Edge inverter system with my solar panels and 3 years into my system, the inverter failed. After discussion with technical support at Solar Edge and their remote troubleshooting, they assigned me an RMA and indicated likely a capacitor failed. This inverter if full of high capacitance value 700 V film capacitors. Solar Edge is having lots of inverter failures in the units based on some googling. Unfortunately, they say I can't even attempt to repair it or I lose my 25 year warranty. BUT they also say typical shipping is 5 to 10 days. When I press them on when they will ship, they then say they are having supply chain problems and have no idea when my replacement unit will ship.
In checking on replacement 700v assorted values of capacitance around 100 microfarads, it's 26+ weeks out. So I am screwed. So much for my solar power inverter that uses high voltage film capacitors. Just venting when I came across this informative video. Any suggestions are appreciated.
Ouch. My Sunnyboy is still going long after 9 years or something, touch wood. Have never opened it though.
Worked with an inverter designer here in Melbourne as a graduate. We blew up a few mosfets in the design phase, but have not heard of a single unit fail yet, not even one intentionally installed in a lightning prone area.
@@EEVblog perhaps you should
Similar issue here so I bought a dead inverter similar to the models I have. After a little disection I found that the electrolytics and silicon parts were all good. the weakest parts were the X2 cap and MOV after the output inductors. these part are in stock if you look around, not too hard to get. Getting the board out really sucks, potentially destructive unless you really look at how it is built. there is reasonable in circuit testing for the most likely to die parts. in the end, the ebay dead unit was one $15 cap away from working. I agree with some commenters to try and switch to X1 caps but have been finding them hard to source.
@ 8:20 It would be interesting to show the audience the difference between several capacitors with the same capacity but volumetrically different - with higher working voltage and thicker metallic layers :)
I opened some capacitors in my life out of curiosity to find out how and why they deteriorate
As I wrote in the original video, almost all X film capacitors lost at least 50% of their capacitance after used for few years.
Seems that they are designed to fail just a short time after the equipment warranty period.
BTW: Before these kinds of non-polar capacitors we used oil-filled paper capacitors, which if sealed did not lose capacitance frequently, nor shorted out."Black Beauties" were made by or for Philco were poorly sealed by design and failed most frequently. Other Bakalite coated capacitors were sealed well they failed very infrequently. (especially RED and orange which are epoxy sealed.) Ron W4BIN
What a throwback to my childhood lol
Loved taking electronics apart, including unrolling capacitors on few occasions.
The transparent line shows an area where there is no connection on either side. Only half the film is directly connected to the terminals anymore and large chunks of the capacitor are only connected through a few connections.
To me it seems like the initial metal film is slightly thinner in the middle. And from that i would hypothesis: The rolling puts a mit more pressure in the middle. More pressure means the insulating layer is compressed more, becoming thinner, and thus forming a consistent point of failure along the strip. When many holes line up they start to cut-off large chunks of the metal-layer, decreasing capacitance and increasing resistance.
Quick, someone do a Fourier transform on the line to estimate the size of the roller!
Thanks for this. I learned some useful facts, and really enjoyed listening to Ron Demcko. In the stuff I work on (vintage audio gear), film caps tend to be less of an issue than electrolytics, the exception being Frako-branded caps, which are a "replace on sight" item. I had not seen damage inside a film cap like this, and I had not considered liquid ingress as being an issue. On the other hand, in vintage audio, one rarely sees X2 caps except across the power switch.
I have had them go short circuit due to continued exposure to over voltage.
This was due to change made by purchasing and they bought a lower voltage rating cap.
As a consequence the caps were setting fire to the resistors in series, as these were snubber circuits on phase controllers.
That was not good, I got to spend a week in the boonies due that and did some interesting trouble shooting.
Very interesting doing failure mode analysis, and power electronics is a rich supply of that.
Schoopage is my new favourite word. And also the definition of Schoop on UrbanDictionary just makes this video even better (obv. NSFW LOL)
I have a TACO brand recirculating pump that uses a certain axial lead capacitor which became very hard to source .. but then I found some, and thought they'd be a good purchase but I believe they might have been culls from a batch because all the leads were cut short .. upon inspection I found out the leads at the potting was open and as the expected just said... It leads the moisture in... And since the pump was in a enclosure outside which pumps extremely hot water... The humidity level is through the roof.... They failed one after another... So much for a cheap and constant source.... I switched to a different TACO pump which in turn had a different capacitor value as well
Ron was awesome! Super insightful for design and failures.
When I was active in building analog circuits I used a lot of Siemens MKM (later MKH/MKT) capacitors.
These are also film capacitors but it is an interesting construction. The film is wound on very large reels in the factory, which are cut to small (~5-8mm) square pieces that get leads connected the same way as these film caps. The cap you get has only flat layers, not the wound construction. It is probably less inductive.
There is no encapsulation, only the later types have a coating over the edges.
They were cheap and nice caps, better for many purposes than ceramic.
(normally they would be 100v or 250v, so suitable for low voltage applications, not across the mains)
This is super fascinating! The backlit patterns and designs in the failing one actually look very, very cool. If blow blown up and printed out, I’d hang it on my wall as art!
I'll try and get some high res macro photo and put them on my Flickr account!
@@EEVblog Thanks! that would be amazing.
It looks like one very long arc. Like when you apply a Tesla coil to a cdrom
@@EEVblog Amazing photos on your Flickr account. You should mention it more often!
Most excellent Dave. I deal with these every day and I have had boards with unexplained drastic capacitor failures when nothing else had failed.
That foil is Ideal for homebrewed capacitor microphone. When disassembling the foil, it smells of acetone.
I wonder how much equipment is thrown due to these failures. I have used a few senseo coffee machines since they came out many years ago. They have one of these capacitors in them. I have replaced the capacitor due to failure in every one of them.
If it's caused by moisture, I'd bet on the film and/or cap being made in some humid area in China and the environmental system not being up to scratch but they didn't want to bin the whole batch to keep production numbers up when reporting to their boss.
Moisture in manufacture is certainly on the failure modes that will manifest with time and continued applied voltage.
It definitely looks like poor process control to me also. The production crew didn't want their "social credit" score to take a hit. Just my $0.02. Fred
Just needs the film to be stored open for a day or so, and this will be enough to adsorb a lot of moisture on the film.
Same thing happened to temperature safety switches in heaters that my employer produces. The engineering samples were completely fine, the manufacturers own samples made at the factory in germany were totally fine, but the ones made in Singapore were made slightly too fast. The plastic didnt fully cure and tripping the sensor bent the internal structure just a tiny little bit, curing the plastic and opening the safety switch permanently. According to the colleague who told me this story it took four months working with the entire team to find the root cause of the problem, going back and forth between the different companies. My guess is that the line workers just want to fulfill their quota and dial in the process just a bit faster here and there without understanding the consequences. I can't blame them either, they're not experts on those parts but poorly paid line workers.
Nothing gets binned in China. Complete failures will be mixed in with good caps and shipped anyway. Well that is what I was told by a work colleague married to a Chinese woman and who lived three months a year out there. Loads of other quite shocking stories as well.....
Isn't the Flux Capacitor a "film capacitor"?
I'll pay that.
@@EEVblog dad joke ;)
An awesome fountain of knowledge. I would listen to him for hours, I wish I had 10% of his experience/knowledge. Thanks for taking the time to share!
thank you for bringing in an expert! I learned more about film caps, and what to do and not do with x2 parts!
Legendary. On hold with the bank and he throws down a highly detailed technical video!!
Only you can make a fun half hour video about a broken capacitor! Very interesting too! Thanks!!
It'd be interesting to put an old, unused one in a vacuum chamber for a few hours. Get as much moisture out as your can, then re-test.
Thanks for the GREAT video. Always interesting finding that it wasn't what you were thinking. I kick myself when I let my bias during testing get in the way.
"Remember: A failed surgery is halfway into a successful dissection!"
Nice come-a-gutsers here. Good educational stuff. I wonder if the cap manufacturing processes will be modified to avoid moisture getting in.
I hope that someone with access to a electron microscope can also open one of these caps and show us how it looks around the healing zones.
Hi Dave, @ 5:48 you showed the metalised film. In the 1970's a company called "Filmcap" started producing Electrolytic Capacitors in outr Village, in Rhosymedre (as in the Ralph (not Raiff) Vaughn Williams Concerto) just 1 mile from MONSANTO (Ruabon) Chemical works in the now World heritage Site of the Pontcysylte Aqueduct)and before long, there was hundreds of yards of this metalised film everywhere around the local villages- people even began to think it was radioactive- and there was quite an outcry about it. The workers there apparently were taking the rejects home for their kids, it was quite a litter problem at the time- then for some reason they disappeared- and production ended- so did the litter problem and a few hundred jobs1
I observed similar film caps used in duct fans loosing capacitance over time causing the fans to loose RPM. Gonna try to unroll one after the next replacement.
Dave! I know it! I just saw 19:42 and this explains all! There is no crack at all! The crack is the area, where the evaporated metal ends on layer one and metal on layer 2 starts. There is no overlapping metal, hence no capacity. Only the very dark spots in the middle are overlapping metal. So all the remaining capacity comes from the very dark spots in the middle, where 2 layers actually overlap. On the first defective cap you had a lot of overlap down the line, which explains, why there is still 100nF. I did not watch it, but I absolutely bet, we will barely see such dark spots on the 2nd, since there is not much left to overlap and give capacity.
Cool video. I learned about this when the Phillips Senseo coffee makers were dying en masse. Same failure pattern. Many thought it's shitty caps and breakthrough events but it was actually moisture damage. Replaced caps of good quality never failed again.
This explains every odd and random failure I have seen with film capacitors but also reinforces why I tell people to never use an old radio or amplifier with the old wax/pio caps in it, I have even seen them explode when used as AC bypass caps! I have a big container full of used x2 caps of various brands and now that my curiosity has been peaked by these failures I am going to go through and actually test a hand full since I always thought these caps had tight quality check guidelines for use in mains filters even with the cheap ones.
in college we were proudly presented with the "advances in technology" that allow the construction of smaller and smaller capacitors at increasing capacities but shortly after graduating I realized that bigger is almost always better ... so to speak
Really interesting, Dave! Great video to unwind... 😜
The best capacitors for that application would be the type used for decades in CRT horizontal deflection circuits, because high currents were the norm in that application.
I fell asleep with youtube on autoplay and woke up to this about halfway though. I had to rewatch the whole thin fully conscious today and this was incredibly cool and informative.
You should consider doing a series where you take apart various discreet components and analyze failure modes. Seeing those small transformers and inductors would be cool.
This was a great discussion. I learned a lot.
I have built several large diaphragm capacitor microphone capsules with capacitor foil and turned brass discs. And a Schoeps style P48 circuit. These have excellent sound for something that simple. The foil was not wide enough, so I 'glued' it to kitchen wrap foil by setting the heat gun to 150 degrees C and slowly sticking the two foils together.
When peeling apart several foil caps, in search of the thinnest metalized foil, I noticed the cheap Chinese caps have a much much thinner metalized layer than trusted brand names, even when spec'd the same. Something else to consider is the size of the non-metalized edge on the foil can vary a lot in the cheap caps.
Lovely microphone, how good do thinners diaphragm perform sonically ?
@@rabbithazel3034 Tension in the diaphragm dictates the low end frquency reponse and thickness the high frequency response. Two layers of kitchen wrap foil with aluminium foil in between sounds very muffled, while one layer with MKP foil already sounds excellent. Just the mkp has the best response, but I could not find caps with foil wider than 22 mm, wich was a bit too small to get to 50 pF. I can recommend these experiments!
@@bentenbroek Try a 250V MKP (they say MKP, if they're actually MKP or not I don't know) capacitor made for power factor correction of electromagnetic ballasts, especially for fluorescent tubes as they tended to be thin and long to fit into the fixtures.
I think on 16uF ones the case was exactly 10 cm long, excluding the terminals and mounting stud if present, I guess the foil inside will be about 1 cm shorter, I don't remember the capacity but I think there were models that were at least 15 cm long, it's been at least 20 years since I dismantled one and at least 15 that I stopped using electromagnetic ballasts, better look for a data sheet.
There are also MKP motor start & run capacitors but those are rated for 450V or more, at least in 230V countries, so I guess the foil has to be thicker.
@@ruben_balea Yes, those might be the solution! I will look into that soon, thank you for pointing to them. I can't wait, but I have none in my parts bins right now.
Looks like a cool tshirt graphic to me. Kinda surf-themed I think.
The stripes are thermo welding so the section doesn't unravel. Film is electrically demetallized for both the core and the outside wrap, so they don't need to add additional film.
But why the lightning style failings are concentrated in the center and not DISTRIBUTED over the WIDTH of the film???
Why the most stress is there???
Those X2 Caps aren't "self-healing", they simply don't fail to a short circuit. In old-timer speak, they "blow clear".
I've had a lot of devices fail due to these being used as Capacitive Droppers. That topology is outrageously unreliable due to the capacitor degradation. Give me a Switch Mode any day, at least they continue to operate even if the BOM Cost is a few cents higher.
They are used in small, low-current, devices like house LED light bulbs (cost under $1) where a switching PS makes no sense both for cost and physical space. Capacitive PS can be extremely reliable if used within current draw limits AND built with GOOD QUALITY caps
@@NICK-uy3nl - ahhhh, yes... but they are rarely (if ever) used within current draw limits AND built with GOOD QUALITY caps 😂
My PowerMate electricity meter failed from a Class X2 dropper cap dying after occasional usage. It is a $250 piece of professional measuring gear, powered by a bloody Capacitive Dropper FFS.
I see too many LED lights and signs flashing away due to failed switchers. Poor component selection kills them.
My house LED lamps are 5 years old and still going strong. All depends on quality of components and operating temps. The design is pretty sound as used in billions of small devices
@@liam3284 - the heat kills the electrolytic caps. Most dedicated non-isolated buck droppers don't really need a smoothing cap, they just get more 100/120 Hz flicker as the cap dies.
The ones that you see flashing on and off are usually from a failed solder joint or LED bond wire fracture.
Dave, it's great that you admit that you were wrong. Sets a great example for those of us with far less expertise to be willing to make mistakes in the process of learning.
Glad you were able to save the interview audio. Mr. Demcko seems like an interesting fellow. 👍️
Yeah, bit goof there on my part. But it turned out at least usable.
My thought is the vaporised material can't escape from the fully potted case. the blotches are likely the vaporised material re-deposited elsewhere on the film
Wow Dave. You really do some cool stuff. Anyone can cut a cap apart, but this is special.
This was super cool!!! Now I wanna take apart my pulse rated capacitors that seem to have lost 30% of their value. Wonder how many holes they have!
The different pattern very likely comes from either different kind of vervoltage stress and/or from the short circuit current (when the plasma is burning there) being limited in a different way (just the ESR when the cap is directly across the mains as e.g. a filter, or in series with a resistor, like e.g. the caps dropper circuit).
The "tiny crack" is enough to kill the capacitance out, when it breaks at both layers, then the current can not flow...
This guy epitomizes my change in personality when I have a circuit I need to repair. "I'm losing my will to live!"
Yeah, major fails. Way back in the late 1950's the capacitor makers actually took out full-page ads in the magazines advertising their new film caps. In the fine print they *did* subtly mention that the capacitors did arc over every second or so. But they still recommended them for all purposes! Even small-signal applications! So it was not unusual to have a 1960's Philco TV that made squealing noises whenever it was turned on as the capacitors "cleared" themselves. Good times.
It looked to me, when you unwound the foil with the "lightning" pattern, that it might be "top foil has upper metalization" and "bottom foil has lower metalization" with the area in the middle forming an actual void between what's left of the layers; and the darker portions looked like where they still overlapped? There was a bit when the layers became undone that looked like that.Maybe the moisture caused some metal to be eroded or galvanized avay? Referring to 19:15 specifically.
Nope, you can see the upper and lower metalised layers still bonded together as a single wrap.
Thanks Dave !! Ive been watching for a video on these..
these failure modes are the reasons that the RIFA capacitors in old computer power supplies are so notorious in the retro-computer crowd. That and their propensity to crack on the outer casing, leak in humid air, and pop violently.
Very interesting part was at 19:14 when you separated two layers of capacitive film. It looks like almost half of each side corroded away and only intersecting areas are those dark blotches, giving the cap it's 19 nF capacitance. It actually looks similar to the 100 nF capacitor in a way. Also wanted to notice bad adhesion of cap with the case for 100 nF 1 year old cap, might be another reason for letting moisture in.
What I don't understand is why we see that distinctive pattern of corrosion where each capacitive film starts corroding away from it's terminal. Is it because unconnected side makes more room for moisture?
I always think your videos are so information you always give great tutorials.Great one dave your a legend
I'm no expert, (entirely self-taught,) so this is wild conjecture, but the thought occurred to me that the burn roughly follows the center of the length of the capacitor because it it was the center of the electrostatic field that was on the capacitor at the time it blew, so the field was guiding the arc just as the field between the electrostatic plates guides the electron beam in a CRT.
Very interesting, thanks Dave!
Not sure if you mentioned it but in addition to the pattern, I think the film also got more transparent in the center.
@3:45 the larger one might have an internal series construction that is actually suitable and recommended for use as a mains dropper. I'll watch expectantly.
Polyester film capacitor variants of x2 have been designed for capacitive power supplies. Tdk Epcos and Vishay have application notes on this but I can't post links here without it being blocked. The polyester film capacitors have a higher temperature rating better humidity properties and the dielectric constant of polyester allows multiple capacitors to fit in the same size enclosure as 1 polypropylene x2 cap. This allows the sharing of the stress, voltage etc to be shared between 2 capacitors. I had an application at work that got me in trouble before I found all of this out. As another reply stated traditional x2 caps have 2 jobs. 1. Never fail short. 2. Perform the required filtering for emc compliance when the device is first tested. Also important to note that an x2 cap across the line is subject to different stresses compared to a capacitor used in series in a capacitive power supply which will have current continuously running through it.
I love the Pulp Fiction 'Get Medieval' reference though it may just be what Dave says when he is out to destroy yet another device!!!
Seems something regarding the temperature, because you see the damage in the middle and there is no damage in the edges where the heat is dissipated by the legs of the capacitor.
So for some visual excitement, get some Panasonic Polysulfone, stacked film SMT caps. These are usually lower voltage, so it doesn't take much to arc them. I was trying them for Class D audio amplifiers as the output filters, because the "poly wanna cracker" films are not available in SMT, though I did find a few at > 10x the normal price and they were 3x the size!. Put them on the output of an audio power amp and apply some pink (or white) noise and Dim the room lights. Enjoy the tiny white fireworks show! 😁
Kool stuff! Enjoyed watching, thanks.
I learned about X film capacitor failures here in the UK in my early years with the "BBC Micro" computer. It was easy to spot when they had failed as flames would come out the rear of the computer.
Here I was, thinking film capacitors were infallible... Great video!
That was really cool! Thanks Dave!
Very interesting. Thanks!
What a legend - I throw out video clips if there's the slightest noise in the background. This man's recording while on hold 😂.
There's nothing I love more than letting out the magic smoke in old electronics with old X2 caps, usually RIFA branded. I work on a lot of old computers, and that's the first thing I check these days because when they wear out, they just love to go bang.
Thank you.
Looks like a bad case of capworm ;-) Very interesting to learn about the likely causes from Ron.
What a great video, we got Ron on the phone, 40 years of capacitor manufacturing experience, he's going to tell us what he thinks
Fascinating - thanks!
Unrolling caps entertained me for hours (no days) in my childhood.
Be me, get a broken power supply in the shop with burnt out polystyrene film caps, get on my computer and go on youtube and see this!! Amazing
The flat caps are wound round, and pressed flat, sometimes baked too to fuse the layers.
My Iberital Espresso machine's rotary pump stopped working, and after many many hours, i managed to find that it is the starting capacitor that failed. From 10uF Down to around 1.5uF.
I replaced it with an oil impregnated 10uF starting cap and i hope the oil will keep it working longer than the regular film cap...
That was an awesome dissection!
Mark of a true engineer, forming a hypothesis, then refining it radically in the face of new evidence. Nice one.
Id assume the low capacity isnt due to 90% material missing but the damage could form "islands" which arent electrically connected anymore to the rest so they dont affect the capacity any longer
Looks like it gradually cut itself lengthwise right down the whole strip. This would make it have half-capacitance... each layer only has contact along one edge.
That pattern that emerges when rolling of the film has a beautiful randomization.
Thanks for this one!
To my eye the marks look very similar to the artworks that are oiled wood shingles that get electric arcs shot through. Could be a similar effect.