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Why film capacitors lose their capacity - MKP X2 capacitor section

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  • Why film capacitors lose their capacity - MKP X2 capacitor section
    Recently, a remote-controlled 230V socket stopped working for me. The relay did not respond to commands sent from the 433MHz radio remote control. Such simple devices use a transformerless power supply, I suspected a short circuit on the zener diode, the reason was damage to the foil capacitor MKP X2 330nF. The capacitor lost its original capacity and at 160nF the power supply to the system was not correct. In newer devices (eg Sonoff) we can find impulse power supplies, in which electrolytic capacitors or SMPS control keys / circuits are damaged. In the case of foil capacitors, probably most of us have heard about their ability to do self-regeneration (depending on the type of capacitor). The breakdown of the dielectric leads to a short circuit and local evaporation of the conductive layer sprayed on the foil, when the layer evaporates, the short circuit is resolved simultaneously. The design of the foil capacitor was visible in old foil capacitors, where there was no casing around the rolled foil constituting a dielectric surrounded by conductive covers on both sides.

    Why film capacitors lose their capacity - MKP X2 capacitor section


    However, can such phenomena reduce capacity by nearly 50%? Looking for information about the reasons for the loss of capacity by the MKT and MKP film capacitors, I found the page link where can you find out that foil capacitors are getting damaged by corona discharges . Corona discharge occurs due to air getting between the foil and the sputtering aluminum covers of the capacitor. The loss of the capacitance of the capacitor reduces the current efficiency of the transformerless power supply, the output voltage is reduced and, for example, the device resets or the relay that requires more power to operate cannot be switched on. The yellow capacitor casings of the timer and power meter are visible below:

    Why film capacitors lose their capacity - MKP X2 capacitor section


    Film capacitors can also be found in anti-interference filters. The capacitors connected between the phase (L) and neutral (N) conductors will be marked with X (in the example X2 - the number indicates the voltage withstand). In anti-interference filters, you will also find capacitors marked as Y, they are connected between the work conductor and the protective conductor.

    Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section


    Measuring the capacity of a damaged and new capacitor that will be installed to repair a wireless outlet:

    Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section


    Let's see what the damage inside the capacitor looks like,
    first the fight with the housing:
    Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section

    We unfold the capacitor and you can see the remains of the sputtered conductive layer:
    Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section

    It turns out, however, that this is the beginning of the capacitor and this "launch tube" constitutes some kind of protective / insulating layer, the last turns of the capacitor look the same. As we expand more, the layer becomes darker.

    Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section

    When we highlight the foil, it turns out that there are visible damages similar to those found in the article. Damage occurs practically along the entire length of the foil.

    Why film capacitors lose their capacity - MKP X2 capacitor section


    I started to wonder if this is really damage, or maybe an imperfect sputtering process, or maybe it is me who cyclically damage the metallization by unwinding the capacitor?

    I decided to develop a functional capacitor desoldered from another device.

    Why film capacitors lose their capacity - MKP X2 capacitor section


    Initially, we have a "starter" foil:

    Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section


    Then uniform metallization appears:
    Why film capacitors lose their capacity - MKP X2 capacitor section

    This confirms that the found article rightly identified the cause of damage to the foil capacitors, the progressive degradation of the sputtered conductive layer lowers the capacitance of the capacitor.

    Have you come across damage to the MKT / MKP foil capacitors, in what devices?

    Why film capacitors lose their capacity - MKP X2 capacitor section


    Source:
    https://gideonlabs.com/posts/ic-emi-mkp-33uf-film-capacitors-failures/
    https://www.ecicaps.com/tech-tools/technical-...failures-metallized-polypropylene-capacitors/

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    TechEkspert
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  • #2
    abart64
    Level 31  
    I think an identical one, also yellow, fell in the coffee grinder. Connected in series in a transformerless power supply. I put an old Russian capacitor from the TV board on 400V and the grinder has been running for 2 years.
  • #3
    TechEkspert
    Editor
    Transformerless power supplies were also used in Soviet flashlights The capacitors used there were also indestructible, while the batteries were quite hopeless.
  • #4
    tmb85
    Level 13  
    At work, we had a similar problem with the capacitors in the flap actuators in the process. These capacitors were connected to the 2-winding motor and when the capacitance decreased, the motors rotated in a random direction causing overshoots in the production process (eg the flap, instead of closing, opened once and then operated correctly - randomly).
  • #5
    TyratrooN
    Level 4  
    I have the most trouble with the so-called "potatoes", foil capacitors flooded with some starch filling. They were used in TV and radio tube receivers from the beginning of the 70s and older. TIMES more capacity than the value written on the housing.
    Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section
    These are just from TV neptun 64r
    Why film capacitors lose their capacity - MKP X2 capacitor section

    They were also just flooded with some resin. they are not as defective as "potatoes" but still worth replacing with newer ones.
    Why film capacitors lose their capacity - MKP X2 capacitor section Why film capacitors lose their capacity - MKP X2 capacitor section
  • #6
    TechEkspert
    Editor
    @TyratrooN I know the ones flooded with resin, they were pretty good,
    I also remember foil capacitors that look like "potatoes" but are inserted into a glass tube covered with tar on both sides. Tar stained everything after dismantling such a capacitor.

    What was the capacity gain phenomenon? The dielectric decreased in thickness / changed properties?

    @ tmb85 this control is something similar to in selsynach?
  • #7
    And41x1
    Level 26  
    For over a dozen years, I have known this phenomenon from practice.
    They used motor capacitors.
    Today, series capacitors in power supplies without transformers are the first and most often the only suspect.
    I mention a lot of them because they are common in roller shutter controllers etc.
    For the purpose of disseminating knowledge, I will mention a similar phenomenon occurring in the power supply resistors of the starting systems in converters.
    These are resistors of the order of several to tens of kilohms, lowering the voltage by about 300 V and for similar reasons as the capacitors in question, their resistance increases.
    As with these capacitors, at some degree of degradation, the power supply stops working.
    Better designs, there were resistors with a higher nominal voltage - they were longer.
    Sometimes two or more series resistors were used.
    Today, series connection is used due to the lower catalog voltage of SMD resistors.
    The nose is degenerative damage to resistors operating at high voltage - ionization control, etc.
    Thus, a voltage drop close to the nominal one causes corona discharge.
    This phenomenon is found in applications where there is a voltage drop, close to the catalog voltage drop.
  • #8
    Jacekser
    Level 21  
    Why are you surprised? Once, long ago (20-30 years), the drying of electrolytes was incidental. I know RTV products (from those years) which, if used today, work without replacement, even the small, most susceptible ones. where it worked. Now it has to work one day more than the warranty. this way of "limiting the use time"
    The European company was the first to take over the "P" in the name! Let's get used to this approach and profit from the service of such devices.
    PS: the worse effect was caused by the lack of contact in the impulse capacitors of the horizontal deflection circuit - the transistor of the system flew out - usually BU508. Sometimes this break appeared incidentally and the measurement of its capacitance was OK, but these capacitors had a quite heavy duty cycle - 16KHz and a high voltage pulse (in monitors the frequency was even higher).
  • #9
    tmb85
    Level 13  
    @TechEkspert It was in such devices, where the controller provided 230V AC to the motor via relays.

    Why film capacitors lose their capacity - MKP X2 capacitor section
  • #11
    kris8888
    Level 32  
    I have encountered this problem in most modern devices in which the power supply is transformerless and the device has a relay inside, the coil of which is powered from this type of power supply. I replace the damaged capacitors with those that I obtained several years ago from CRT TV sets (from horizontal deflection blocks). They are of better quality than their modern counterparts.
    It is good practice to add a properly selected resistor in parallel to the capacitor to reduce the current flowing through the capacitor at least a little.
  • #12
    avatar
    Level 35  
    Hi - and isn't the result of the above-mentioned defects sometimes incorrect thickness of the foil used, ecology in the production of plastic (foil) + better sealing of the capacitor? Film sputtered capacitors have such an "advantage" that they repair themselves, ie as a result of a short circuit - some of the film evaporates - the capacitance of the capacitor is reduced but there is no short circuit either. Part of the resulting gas remains in the condenser, pressing against the remaining turns - destroying them mechanically.
    These "good" additives for plastics are not ecological - it also degrades the plastic itself, which may be more susceptible to biodegradation and the penetration of moisture inside.
    And as for the corona discharge - once foil capacitors could withstand 200% Un - so there should be no corona phenomenon at 100 or 120% Un
  • #13
    #Andrzej#
    Level 9  
    Hello
    I had the same situation, the CO furnace controller [from a well-known company] was turning off the message high mosfet temperature in the power supply the capacitor had less than 300nF of capacity at 680 nF declared after 3 years of work repair cost for them PLN 200 cost of the capacitor PLN 2 only for which company to buy. A dozen years ago I made a twilight switch on USSR capacitors and works to this day.
  • #14
    rb401
    Level 36  
    TechEkspert wrote:
    This confirms that the found article rightly identified the cause of damage to the foil capacitors, the progressive degradation of the sputtered conductive layer lowers the capacitance of the capacitor.


    Strictly speaking, we have an in-depth description of the damage mechanism here, and not the real reason and how to prevent it.

    I just started replacing the capacitors in a series of identical motion sensors, where the capacitors fell very repetitively, for a year or two and a failure:
    Why film capacitors lose their capacity - MKP X2 capacitor section
    this one in about a year "went down" from the nominal 330nF to 140nF. Others in this series are similar.

    But it is still unclear to me why the X2 type capacitors strictly dedicated to continuous operation at full voltage of the standard network, factory-tested in an extended manner against "ordinary" capacitors with reference to numerous safety standards, show a repeatable manufacturing defect. Because you could call it that.
    And they do not have to, because, for example, checking the X2 capacitor with the same main parameters as the incident ones in another device, working in the same system for 18 years without interruption, it turned out that it did not show a drop in capacity, even beyond the tolerance range.

    And here comes the question of what specific capacitors to use in the event of a broken one, so as not to come back to the topic anymore. Especially that, as can be seen from some statements, such failures can be very severe and costly in some areas.

    And just looking for some certain capacitors to replace, I came across an interesting document from Epcos:


    Why film capacitors lose their capacity - MKP X2 capacitor section
    https://www.tdk-electronics.tdk.com/download/...cfb5eade04ff/pdf-emiapplicationnote-x1-x2.pdf

    It shows that in such applications as capacitor power supplies, having the X2 class and compliance with numerous standards, the logos of which are numerous on the housings, does not imply that such a capacitor will be optimal. And here the observation of my colleague kris8888 is confirmed that in this application, "ordinary" polypropylene capacitors (of course, appropriately selected parameters) work just as well, or better, than those classic X2 strictly dedicated to work parallel to the mains.



    TechEkspert wrote:
    What was the capacity gain phenomenon? The dielectric decreased in thickness / changed properties?


    Maybe you're right. In my opinion, it is possible that the paper, a porous material from the ground, "compacted" over time due to the stresses in the coil.
    And it seems to me that this is perhaps a general feature of paper capacitors, because I have dealt with this phenomenon myself, although they were not potatoes.

    I recently revived a Soviet device from the Brezhnev era. There was an RC sine generator that couldn't be set to the nominal frequency. And only the measurement of the capacitors showed the reason.
    There were MBM capacitors, i.e. paper, metallized:
    Why film capacitors lose their capacity - MKP X2 capacitor section

    And for example, from the nominal 250nF they went to about 330nF, which is well beyond the tolerance, all copies of this type in this device more or less equally.
    Here, more did not mean betterso I pulled out the weeds and in their place I gave just a few years younger polyester miflexes, which, despite their age, held the capacity in accordance with what was written on them.
  • #15
    Jacekser
    Level 21  
    It seems to me that the power is "pumped" through the capacitor and this is the reason for the degradation of the coated linings (I do not know the technology of producing these capacitors). Probably the "green" production guidelines do not ensure the durability of MTBF specified in the data (or maybe they do -?). Since you write that it takes place after about 2 years, it is after the warranty and you need to buy a new one. Perfectly matched consumption. Somehow washing machines, refrigerators can work with this type of power supply for years.
  • #16
    Janusz_kk
    Level 28  
    rb401 wrote:
    I just started replacing the capacitors in a series of identical motion sensors, where the capacitors fell very repetitively, for a year or two and a failure:

    this one in about a year "went down" from the nominal 330nF to 140nF.


    In my opinion, the main reason is too high impulse currents flowing through the capacitor, each inclusion generates such inclusion, it is limited by the 100om resistor visible in the picture, but it is too small, I give 330om to 1kom resistors in this place depending on the current and the capacitors are almost eternal.
    I do the same with small transformers
  • #17
    żarówka rtęciowa
    Level 36  
    Hello

    Currently, transformerless power supplies based on a series capacitor are replaced by miniature switching power supplies on an integrated circuit of the LNK304 type or similar. They are mainly found in household appliances and light sources with LED diodes.

    And41x1 wrote:
    For over a dozen years, I have known this phenomenon from practice.
    They used motor capacitors.


    Capacitors to compensate the reactive power of high pressure lamps and fluorescent lamps were also able to lose capacity.
  • #18
    kris8888
    Level 32  
    Jacekser wrote:
    It seems to me that the power is "pumped" through the capacitor and this is the reason for the degradation of the coated linings (I do not know the technology of producing these capacitors).

    Not so much power, but quite a lot of current flows, from a few to a dozen or so mA, which is a considerable value for a very thin, sputtered layer of capacitor linings and causes their degradation.
    Jacekser wrote:
    Somehow washing machines and refrigerators can work with this type of power supply for years.

    In washing machine or refrigerator controllers, power is rather not used through a serial capacitor, too much current is needed to power the controller. There is, however, a transformerless power supply, based on the principle of a pulse converter, but without galvanic separation from the mains (based on the LNK series ...
  • #19
    Jacekser
    Level 21  
    kris8888 wrote:
    In washing machine or refrigerator controllers, power is rather not used through a serial capacitor, too much current is needed to power the controller. There is, however, a transformerless power supply, based on the principle of a pulse converter, but without galvanic separation from the mains (based on the LNK series ...

    I repaired a few with this power supply (problems other than the power supply) and they have been working for about 15 years. A week ago I was repairing my Polar PTL819 sister washing machine (Whirlpool L1373) with LNK304 released. :) I do not repair this type of equipment constantly, only incidentally.
    For example, I have repaired this:
    https://www.elektroda.pl/rtvforum/topic2330767.html
  • #20
    TechEkspert
    Editor
    When I post material on elektroda.pl, it usually happens that either I learn something very interesting from the comments, or later the information from the material comes back to my mind when I solve a problem.

    Today I saw a friend who has an old Promień LE-1 flashlight charged with 230V in his garage. I have already told him more than once that he should leave a LED flashlight there for PLN 5 and it will work for a year on one battery, because he charges the old flashlight all the time. Today I told him that probably the batteries are long to be thrown away and the bulb is a poorly efficient light source. He did not want to replace this flashlight, well every age has its rights and if someone does not want something, it's difficult. He also mentioned that the batteries are good because when the flashlight is charged, it holds, only the charging process takes a very long time.

    Then I put the facts together :) and I said okay I'll fix this old flashlight. After unscrewing it, it turned out that the miflex had a capacity of 80nF instead of 680nF. I replaced the capacitor and after a short charge the bulb was already glowing. It works :) let him have it and be happy ;)


    Why film capacitors lose their capacity - MKP X2 capacitor section
  • #21
    kaczodp
    Level 13  
    The old truth, you want to buy cheap and you buy well twice for the first cheap.
  • #22
    szeryf3
    Level 21  
    For me, when something old to repair lands on the table, I first look at the capacitors. Something I never believed them.
  • #23
    ojciec
    Level 33  
    TechEkspert wrote:
    instead of 680nF it had a capacity of 80nF

    I wonder who put it there, the manufacturer, the owner of the flashlight (old repair), the working voltage
  • #24
    TechEkspert
    Editor
    I will say yes, it also choked me ... It is 250V, probably DC voltage, as long as I read the markings correctly and who knows if it was not the equivalent of MKT, unless it is material savings and this fuse is there for a reason ...
  • #25
    ojciec
    Level 33  
    The capacitor is DC voltage (MKSE type); a long time ago I put these on 400V (should be 630V) also permanent as a backlight on one LED for power switches; to this day they work