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Fascinating failure mode of metallised film capacitors.

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Kind: captions
Language: en

00:00:00.120
I have just had a bit of an epiphany a
00:00:02.570 00:00:02.580 bit of a revelation shall we say about
00:00:05.329 00:00:05.339 these capacitors being used em for power
00:00:07.550 00:00:07.560 supplies and LED lamps and and time
00:00:10.490 00:00:10.500 switches and these little remote control
00:00:11.990 00:00:12.000 units now this time switch is kind of
00:00:15.410 00:00:15.420 dead
00:00:15.860 00:00:15.870 why show happens this time switch is
00:00:17.990 00:00:18.000 that when it turns on instead the relay
00:00:19.580 00:00:19.590 community just makes a loud buzzing
00:00:20.870 00:00:20.880 noise and likewise this remote control
00:00:24.050 00:00:24.060 switch when it filled its failure mode
00:00:28.849 00:00:28.859 was that when you press the button it
00:00:30.410 00:00:30.420 turned on then after a very short time
00:00:32.269 00:00:32.279 later on back off again and you press
00:00:35.090 00:00:35.100 the button it would turn back on and
00:00:36.530 00:00:36.540 then it would after a while it would
00:00:37.610 00:00:37.620 turn back off it just wouldn't hold on
00:00:39.350 00:00:39.360 at all and for some reason I was just
00:00:44.389 00:00:44.399 talking to someone about their the
00:00:45.799 00:00:45.809 capacitors and they said yeah they can
00:00:47.600 00:00:47.610 progressively feel and the reducing
00:00:49.750 00:00:49.760 capacitance when they do that and I
00:00:51.920 00:00:51.930 thought that's quite odd and I wonder if
00:00:55.040 00:00:55.050 that's what's actually happening here so
00:00:57.319 00:00:57.329 I measured the capacitor in here and it
00:01:00.650 00:01:00.660 cures at 47 nano farad and I have to say
00:01:03.290 00:01:03.300 it said four seven four on the top and I
00:01:06.830 00:01:06.840 thought oh that's BAM possibly an
00:01:10.250 00:01:10.260 indication it is 47 nano farad is not
00:01:13.219 00:01:13.229 really for it's not really a good
00:01:15.020 00:01:15.030 indication it's just I'd jump to
00:01:16.460 00:01:16.470 conclusion and then I looked at the side
00:01:18.499 00:01:18.509 of it and because I think of a 47 nano
00:01:20.960 00:01:20.970 fired as being something more like this
00:01:22.670 00:01:22.680 size and this was really big and it
00:01:25.249 00:01:25.259 turns out it's supposed to be 229 of
00:01:27.230 00:01:27.240 fired but it was just measuring 47 nano
00:01:30.080 00:01:30.090 fired and I've got another unit and I
00:01:34.100 00:01:34.110 without really taking it - that's too
00:01:35.990 00:01:36.000 much mean I've opened up and access the
00:01:38.780 00:01:38.790 connections inside and measured across
00:01:41.149 00:01:41.159 the same connections and it measured
00:01:44.090 00:01:44.100 about 230 nano fired so definitely the
00:01:47.389 00:01:47.399 capacitor in here had degraded so I
00:01:50.450 00:01:50.460 opened it up and these capacitors I'll
00:01:53.179 00:01:53.189 give you a we a look at what's actually
00:01:55.880 00:01:55.890 how they're made these are called
00:01:58.940 00:01:58.950 metallized film capacitors and basically
00:02:01.340 00:02:01.350 the capacitor typically consists of an
00:02:04.280 00:02:04.290 insulator with a metal film and either
00:02:06.709 00:02:06.719 side and the area of the film and the
00:02:09.050 00:02:09.060 thickness eventually to determine the
00:02:10.430 00:02:10.440 capacitance so what they do is metal
00:02:12.589 00:02:12.599 eyes film capacitors
00:02:13.700 00:02:13.710 as if this is the film and that's the
00:02:16.820 00:02:16.830 metallized side they lee another film
00:02:20.540 00:02:20.550 against it and it's got a metallized
00:02:23.990 00:02:24.000 side and the thickness of the plastic in
00:02:27.830 00:02:27.840 between the two layers of metal it gives
00:02:30.740 00:02:30.750 the this voltage rating the capacitor
00:02:32.690 00:02:32.700 it's it's dielectric rating and the
00:02:36.110 00:02:36.120 total area of the metallized foil will
00:02:39.110 00:02:39.120 determine natural capacitance and to
00:02:41.630 00:02:41.640 make it compact they take strips of this
00:02:43.610 00:02:43.620 and this of the basically this spiral
00:02:47.390 00:02:47.400 them together like that and you end up
00:02:52.460 00:02:52.470 with they're quite a large area of metal
00:02:55.100 00:02:55.110 with the thin plastic insulating it and
00:02:58.780 00:02:58.790 what happens with this is that if you
00:03:01.550 00:03:01.560 get there if you get the layer of the
00:03:04.160 00:03:04.170 insulation and the metallization on the
00:03:06.980 00:03:06.990 top and the metallization the bottom
00:03:08.690 00:03:08.700 effectively then if the plastic breaks
00:03:11.720 00:03:11.730 down if there's a high voltage spike and
00:03:14.090 00:03:14.100 it makes a hole through that then in the
00:03:16.520 00:03:16.530 immediate vicinity it does flashover and
00:03:18.350 00:03:18.360 it just clears some metal on either side
00:03:21.170 00:03:21.180 and it creates this a little island
00:03:23.420 00:03:23.430 round the hole in either side and that
00:03:25.400 00:03:25.410 is what's called self-healing it
00:03:27.410 00:03:27.420 basically heals itself that repairs
00:03:29.990 00:03:30.000 itself in a sort of controlled manner
00:03:31.660 00:03:31.670 but what's actually happened in the case
00:03:33.830 00:03:33.840 of this capacitor and I actually took it
00:03:37.550 00:03:37.560 to bits and unwound all the foil in the
00:03:40.280 00:03:40.290 suggestion of a friend he said it would
00:03:41.630 00:03:41.640 be really interested to see you know
00:03:43.340 00:03:43.350 what it looked like and it's quite
00:03:45.560 00:03:45.570 unusual I took a bit of it and I've
00:03:48.050 00:03:48.060 stuck it down to a bit of paper and then
00:03:50.120 00:03:50.130 I took a photo and this is the area that
00:03:53.930 00:03:53.940 supposed to be metallized but it's
00:03:55.430 00:03:55.440 gradually eroded the metallization away
00:03:57.950 00:03:57.960 to the point that you know it's all
00:03:59.420 00:03:59.430 these little islands and it's it's
00:04:01.520 00:04:01.530 really reduced amount of metallization
00:04:03.170 00:04:03.180 and the matching foil the other
00:04:06.140 00:04:06.150 electrode of the fall was kind of solid
00:04:10.790 00:04:10.800 and it hadn't eroded in the same way but
00:04:14.060 00:04:14.070 it had this mottled effect the middle of
00:04:16.310 00:04:16.320 it where that had gradually been eating
00:04:17.900 00:04:17.910 away and that's what made that reduced
00:04:20.840 00:04:20.850 in the value and that is ultimately why
00:04:23.390 00:04:23.400 it couldn't operate properly because
00:04:25.700 00:04:25.710 what was happening was the reduced
00:04:27.320 00:04:27.330 value of the capacitance meant that that
00:04:28.939 00:04:28.949 the post black pastor was charging up it
00:04:31.460 00:04:31.470 was enough to run the electronics the
00:04:33.679 00:04:33.689 electronics which are actually mounted
00:04:35.450 00:04:35.460 on this side and as soon as you press
00:04:39.260 00:04:39.270 the remote control button and it tried
00:04:40.790 00:04:40.800 to bring the real Ian that was the
00:04:42.439 00:04:42.449 problem because there really needed a
00:04:44.929 00:04:44.939 good 20 Mille amps to actually pull in
00:04:49.399 00:04:49.409 and that dragged the because the
00:04:52.040 00:04:52.050 capacitor could no longer supply that
00:04:53.779 00:04:53.789 current it dragged the voltage
00:04:55.159 00:04:55.169 progressively down on the electrolytic
00:04:56.689 00:04:56.699 until it cut out and reset the circuitry
00:04:59.089 00:04:59.099 and likewise with this time switch that
00:05:02.119 00:05:02.129 it was trying to bring it bring in there
00:05:04.369 00:05:04.379 really but because the capacitor has
00:05:06.200 00:05:06.210 filled in this one as well and it's not
00:05:08.839 00:05:08.849 quite dramatic but it's obviously it's
00:05:10.399 00:05:10.409 just been operation is borderline I
00:05:12.020 00:05:12.030 think it's gone from 339 of fired and
00:05:14.510 00:05:14.520 here down to about 220 or something like
00:05:17.629 00:05:17.639 that but it's enough that when instead
00:05:20.209 00:05:20.219 of actually bringing the really and that
00:05:21.980 00:05:21.990 unit just made a loud buzzing noise as a
00:05:24.499 00:05:24.509 70 like electrical arcing but it was
00:05:26.570 00:05:26.580 just the really crackling and buzzing
00:05:28.010 00:05:28.020 batteries and forwards down pull in and
00:05:30.110 00:05:30.120 it's all down to the fact that the
00:05:32.059 00:05:32.069 capacitors have progressively filled and
00:05:34.820 00:05:34.830 it makes me wonder
00:05:36.439 00:05:36.449 so LED lighting there me using smaller
00:05:41.029 00:05:41.039 and smaller capacitors which means that
00:05:42.740 00:05:42.750 making the film thinner and thinner and
00:05:44.570 00:05:44.580 thinner in here the insulation film and
00:05:46.809 00:05:46.819 that ultimately means that over time
00:05:50.140 00:05:50.150 when lives really skimped on the
00:05:52.430 00:05:52.440 capacitor ratings there's a very good
00:05:54.709 00:05:54.719 chance that these LED lamps will
00:05:56.959 00:05:56.969 gradually reduce physically in power not
00:06:00.499 00:06:00.509 just intensity I mean they will reduce
00:06:02.089 00:06:02.099 in intensity but they're actually it
00:06:04.339 00:06:04.349 won't just be down to LED progressive
00:06:06.409 00:06:06.419 failure and forceful failure the actual
00:06:08.659 00:06:08.669 intense of the light will go down
00:06:10.899 00:06:10.909 because it's simply drawing less current
00:06:13.879 00:06:13.889 because the capacitor that rations that
00:06:16.309 00:06:16.319 current threat is a is progressively
00:06:19.369 00:06:19.379 getting lower and lower and value and
00:06:21.439 00:06:21.449 letting less and less current through in
00:06:23.450 00:06:23.460 each half wave so that was really
00:06:25.850 00:06:25.860 interesting and it's just something that
00:06:27.890 00:06:27.900 suddenly lots of things make sense
00:06:30.850 00:06:30.860 dimmer is starting to feel and
00:06:34.930 00:06:34.940 interference suppression capacitor
00:06:37.070 00:06:37.080 starting to feel because you know you
00:06:38.839 00:06:38.849 don't see it happening unless you
00:06:40.939 00:06:40.949 actually went
00:06:41.420 00:06:41.430 measure those capacitors you're not
00:06:42.860 00:06:42.870 going to realize that the interference
00:06:44.840 00:06:44.850 suppression capability of that capacitor
00:06:47.240 00:06:47.250 the ability to past those spikes and
00:06:49.070 00:06:49.080 transients is gradually reducing and
00:06:51.860 00:06:51.870 that could cause things like processor
00:06:54.080 00:06:54.090 crashes because you know the transients
00:06:56.360 00:06:56.370 are being removed effectively nema so
00:06:58.550 00:06:58.560 that was really interesting it's just
00:07:00.020 00:07:00.030 you know why is it taking me so long to
00:07:02.180 00:07:02.190 discover this is really interesting
00:07:04.730 00:07:04.740 indeed and it means that things like
00:07:06.500 00:07:06.510 this can be repaired you simply take the
00:07:08.630 00:07:08.640 capacitor and stick a Newman in and that
00:07:10.370 00:07:10.380 gives a complete new lease of life
00:07:12.200 00:07:12.210 likewise I know these are cheap and
00:07:14.210 00:07:14.220 nasty tank locks but you know it's easy
00:07:17.330 00:07:17.340 just to stick a new capacitor in that
00:07:18.980 00:07:18.990 and it will give it a new lease of life
00:07:20.450 00:07:20.460 again so yeah metal eyes filmed pastures
00:07:23.630 00:07:23.640 they do progress they feel and you think
00:07:26.750 00:07:26.760 electrolyte electrolytic capacitors they
00:07:29.330 00:07:29.340 tend to keep their capacitance value but
00:07:32.030 00:07:32.040 they're sort of internal resistance goes
00:07:34.220 00:07:34.230 up as they dry out the actual liquid
00:07:36.020 00:07:36.030 electrolyte in them dries out but in
00:07:38.060 00:07:38.070 this case the actual plates are
00:07:40.040 00:07:40.050 gradually vanishing and that value of
00:07:42.710 00:07:42.720 the capacitance is what's actually
00:07:44.210 00:07:44.220 suffering in these it's progressively
00:07:46.160 00:07:46.170 going down so very interesting very
00:07:48.560 00:07:48.570 useful to know

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