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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 1st Aug 2020, 6:06 pm   #1
Uncle Bulgaria
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Default Help identifying film capacitor material

Is there some standard for coating colour indicating underlying materials?

Here, I have two capacitors marked MKT and MKC, but the third has only the value and 'U' which I can't find a reference for.
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Old 1st Aug 2020, 7:21 pm   #2
vidjoman
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Default Re: Help identifying film capacitor material

Plenty to read here
https://en.wikipedia.org/wiki/Film_capacitor
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Old 1st Aug 2020, 7:27 pm   #3
Uncle Bulgaria
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Default Re: Help identifying film capacitor material

Thanks. I did have a look through that page, but while it lists many of the abbreviations it doesn't say (unless I've missed it) whether there's a standardised colour or outer coating for different types of capacitor. I ask because the circuit I'm making specifies MKT, and I wondered when I would use these ones that are unidentified or if they'd just sit in my drawer.
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Old 1st Aug 2020, 7:33 pm   #4
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Default Re: Help identifying film capacitor material

I don't believe there is a standard. Wima certainly put their MKT, MKP, MKS, FKP and FKS capacitors in their 'usual' red rectangular packages. They also packaged FKS and FKP (and maybe others) in blue. You have a brown MKC one of theirs. I suspect they used what they had, or what the Marketing Dept thought looked suitably snazzy.

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Old 1st Aug 2020, 7:52 pm   #5
Uncle Bulgaria
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Default Re: Help identifying film capacitor material

I do have a few of those bright red square ones, as well as the brownish-red Wimas - they have quite a lot of printing on which is very handy! In a practical sense, are there many occasions when it's critical which type of film is used? Otherwise, as I have a reasonable number of these epoxy covered reddish ones in the 10-100nF range I'll just use them generally. I know if I'm doubtful about them then they'll sit in the drawer until I reach an age where I need to clear out and they'll be dumped on someone else!
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Old 1st Aug 2020, 9:36 pm   #6
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Default Re: Help identifying film capacitor material

Whether it's critical or not will depend on the application, no doubt. I work mostly in audio, where reliability and durability are more important than anything else. The actual dielectric doesn't matter much, but construction quality does. The only exception is where customers are interested in authenticity. This can effect value. Few people think money is unimportant .

In my edition of Horowitz and Hill The Art of Electronics there is a table of capacitor dielectric properties, including Accuracy, Temperature stability and Leakage. Rated against these criteria polyester gets Good, Poor, Good. Polycarbonate gets Excellent, Excellent, Good. Polypropylene gets Excellent, Good, Excellent. So at least two people think they're not all the same.

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Old 1st Aug 2020, 9:37 pm   #7
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Default Re: Help identifying film capacitor material

Searching for "MKT capacitor" gives metalized polyester and "MKC capacitor" gives metallized polycarbonate (apparently no longer made by WIMA due to the dielectric being discontinued by the only supplier).

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Old 1st Aug 2020, 11:13 pm   #8
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Default Re: Help identifying film capacitor material

And polycarbonate thus discontinued by every capacitor maker at the same time! (mid-1990's). Bayer was the polycarbonate film manufacturer.
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Old 2nd Aug 2020, 12:30 am   #9
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Default Re: Help identifying film capacitor material

Also https://en.wikipedia.org/wiki/Capacitor_types

The third one along looks like what we used to call a 'greencap' (back when they were green)
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Old 2nd Aug 2020, 12:45 am   #10
Uncle Bulgaria
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Default Re: Help identifying film capacitor material

So, the consensus is that there is none.

I have a lot of these reddish ones among treasures in a set of drawers sold to me by whiskas of this parish. It seems (I mostly dabble in audio, though the small values will probably come in handy in radio repairs) that I can use them with impunity going by the value alone. I've enjoyed what I've read of 'The Art of Electronics' though much goes over my head, and I think in the undemanding audio field (compared to gigahertz propagation) the difference between 'excellent' and 'good' will be moot.
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Old 2nd Aug 2020, 2:45 am   #11
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Default Re: Help identifying film capacitor material

Likely polyester film given the age and technology and simply statistically. Could possibly be something 'better' but not 'worse' so will be usable where MKT is specified, for most intents and purposes. The U doesn't directly indicate that as far as I can tell but it generally looks like one. I presume there's no manufacturers logo on it?
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Old 2nd Aug 2020, 2:59 am   #12
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Default Re: Help identifying film capacitor material

Not that I can make out. Some have 'U', some have 'A' and some a few dots as in my post #10. The letters could be a logo, I suppose, but the capacitors all look very similar so are unlikely to be from different places.

I thought polyester was always those silver/clear tubes in low values.
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Old 2nd Aug 2020, 5:54 am   #13
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Default Re: Help identifying film capacitor material

Likely the letters are tolerance codes http://www.iequalscdvdt.com/Markings_and_Codes.html
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Old 2nd Aug 2020, 5:59 am   #14
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Default Re: Help identifying film capacitor material

The silver/clear tubular ones sound like polystyrene.

Sprague did polyester/mylar ones with an orange overcoat other firms used blue or mustard.

Colour isn't much of a guide unless you know the maker.

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Old 2nd Aug 2020, 9:04 am   #15
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Default Re: Help identifying film capacitor material

Re - the colour of film caps, I spend happy hours pulling radial film caps and other goodies off scrap PCB's like most of us here. From what I've found they used a wider variation of colour in the past. I've got sky blue ITT's, yellow, orange, dark blue, perlescent green, dark green, black, a sort of wishy washy egg colour and the dark red ones as per Uncle's pics off vintage tele, VCR boards etc. Massive heavy odd coloured dark reds ones seem to crop up in CRT type tele boards, I've yet to find a use for a 690n 250v cap the size of a matchbox.

Now if you order a film cap, radial that is, they tend to be either orange or dark green and maybe dark red. The only outlier are Wima made caps, they going for the red body white print. Maybe in the past more women were involved then as now, in cap body design and thus chose weird and wonderful body colours to match the curtains/carpet, that or there was one central cap designer with a sense of humour, "what colour do you want" .... "I think i'll have minty green or sunrise over Octoon forest on a mid May morning during a partial eclipse"

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Old 2nd Aug 2020, 9:10 am   #16
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Default Re: Help identifying film capacitor material

Often the difficult part is to find out the working voltage which is usually a letter code that seems to vary by manufacturer.
We used to use 'green' ones but they were rated as 100v Dc. Others with a different code letter were 400 volts. Size was not always any indicator either.
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Old 5th Aug 2020, 2:51 pm   #17
Uncle Bulgaria
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Default Re: Help identifying film capacitor material

Polly put the kettle on. Of course you're right David - I meant polystyrene.

Thanks for that link Terry VK5TM - I thought letters were usually tolerance codes, but couldn't find any reference to the 'U' for example. Now your page suggests it could be -10%/+75%!

It is a nice reddish colour, and as other members of the family consider that drawers of components really look like a sweetshop, it's a bit dull they're not so many different colours these days. For some the engineering elegance might be the joy, but as that's over my head the simple variations of eye-detected wavelengths are pleasing during a project. I like bright orange Philips ones I've just found in my Uher VG 840.

It looks like a good idea to buy freshly picked ones for certain applications.
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