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Polystyrene Caps for General Purpose? |
roglok
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 Posted: Mon Nov 26, 2012 4:50 pm Post subject: Polystyrene Caps for General Purpose? |
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I recently got a big assortment of polystyrene caps for cheap.
What I know is that they have a high temperature stability and are therefore a prime choice when it comes to timing caps in VCOs and other applications that require a stable frequency.
What else are polystyrenes good for? Can they be used as general purpose caps? Would this just be overkill or are there any downsides?
The only thing that comes to my mind is that they are apparently sensitive to excessive heat but I haven't managed to destroy one yet... |
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CJ Miller
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| Posted: Mon Nov 26, 2012 5:11 pm Post subject: |
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They are major overkill for general purpose use. Only widely available in the picofarad range, and comparatively expensive. Only real downside I'd imagine is that foil caps like these are probably a bit more inductive than others, but for 0-20khz this is probably not generally an issue. Also they are more physically fragile than most caps, in that they can easily melt if not soldered with proper precautions.
But when you need them, they are great to have around. |
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consumed
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| Posted: Mon Nov 26, 2012 5:18 pm Post subject: |
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| CJ Miller wrote: | | They are major overkill |
and much easier to accidentally destroy
just sayin
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ElektroSteam
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| Posted: Mon Nov 26, 2012 5:58 pm Post subject: |
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They also tend to be larger than equivalent NP0 ceramic caps. Note they most certainly do work very well even at RF frequencies up to 30MHz or so, they are not for audio use only. They have about the same inductance as an equivalent piece of copper wire.
I would save them for when you really need them, not sure if they are still being manufactured. A while back there was some talk about the German(?) manufacturer of the polystyrene foil shutting down the relevant production facility. |
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daverj
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| Posted: Mon Nov 26, 2012 8:42 pm Post subject: |
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First, are you sure they're polystyrene and not some other type of film capacitor (polyester, polypropylene, etc...)?
They're good not just for oscillators, but also filters, sample & holds, slews, and anything else with a timing cap.
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frijitz
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| Posted: Mon Nov 26, 2012 8:48 pm Post subject: |
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Once again, I did some careful measurements of polystyrene vs NP0/C0G ceramics in a high-performance VCO and found virtually identical behavior. In fact, the ceramics have a smaller temperature coefficient. Polystyrene has not been manufactured in many years as far as I can tell, because of the high toxicity of styrene.
Ian |
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Dr. Sketch-n-Etch
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| Posted: Tue Nov 27, 2012 1:21 am Post subject: |
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| frijitz wrote: | Once again, I did some careful measurements of polystyrene vs NP0/C0G ceramics in a high-performance VCO and found virtually identical behavior. In fact, the ceramics have a smaller temperature coefficient. Polystyrene has not been manufactured in many years as far as I can tell, because of the high toxicity of styrene.
Ian |
I have never used polystyrene caps personally, but I have found that polypropylene film caps (I prefer the WIMA ones which look like little red bricks) work very well for filters. A filter will self-oscillate very robustly with these, and may not with the equivalent value C0G ceramics. Indeed, I can often fix an errant filter simply by replacing the caps with WIMA PPE films.
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frijitz
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| Posted: Tue Nov 27, 2012 2:58 am Post subject: |
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| Dr. Sketch-n-Etch wrote: | | I have never used polystyrene caps personally, but I have found that polypropylene film caps (I prefer the WIMA ones which look like little red bricks) work very well for filters. A filter will self-oscillate very robustly with these, and may not with the equivalent value C0G ceramics. Indeed, I can often fix an errant filter simply by replacing the caps with WIMA PPE films. |
Yes, very low dielectric absorption. But what is their temp coeff?
Ian |
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roglok
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| Posted: Tue Nov 27, 2012 3:41 am Post subject: |
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Hey all, thanks for your answers.
| daverj wrote: | | First, are you sure they're polystyrene and not some other type of film capacitor (polyester, polypropylene, etc...)? |
They were sold to me as polystyrene and sure look like the ones in my parts bin. Here is a quick shot showing some of the caps (about half the lot):
| frijitz wrote: |
Once again, I did some careful measurements of polystyrene vs NP0/C0G ceramics in a high-performance VCO and found virtually identical behavior. |
I've read that before, Ian. But I'm not quite sure what NP0/C0G means. Are those standard multilayer ceramics?
The thing is I already have all these caps, so my question was less about what they can be replaced with than the other way around. I just don't feel like hoarding all of them - Pretty certain I won't build 200 VCOs and 150 S&H circuits 
That said, if anyone is up for trading components - let me know... |
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home_listening
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| Posted: Tue Nov 27, 2012 4:46 am Post subject: |
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| I'm Jealous, they look lovely. |
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ringstone
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| Posted: Tue Nov 27, 2012 6:02 am Post subject: |
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| roglok wrote: | | But I'm not quite sure what NP0/C0G means. Are those standard multilayer ceramics? |
It refers to a type of dielectric (the material in capacitors that gives them their properties as an electronic component) that is highly stable in value with regard to temperature variation:
http://en.wikipedia.org/wiki/NP0
Polystyrene capacitors also share similar properties with regard to temperature stability. Ceramic capacitors are classed with regard to this and other properties, into three main classes (also known as low, mid and high k).
BTW are those the styrenes that were being sold on Ebay? I nearly bought those myself...
Cheers
Blair
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roglok
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| Posted: Tue Nov 27, 2012 6:42 am Post subject: |
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| ringstone wrote: |
It refers to a type of dielectric (the material in capacitors that gives them their properties as an electronic component) that is highly stable in value with regard to temperature variation:
http://en.wikipedia.org/wiki/NP0
Polystyrene capacitors also share similar properties with regard to temperature stability. Ceramic capacitors are classed with regard to this and other properties, into three main classes (also known as low, mid and high k).
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OK, cool. Thanks. So I guess when buying ceramic capacitors C0G/NP0 are generally the ones one should get?
| Quote: | | BTW are those the styrenes that were being sold on Ebay? I nearly bought those myself... |
maybe?
http://www.ebay.de/itm/321012198737 |
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ringstone
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| Posted: Tue Nov 27, 2012 6:53 am Post subject: |
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| roglok wrote: | | ringstone wrote: |
It refers to a type of dielectric (the material in capacitors that gives them their properties as an electronic component) that is highly stable in value with regard to temperature variation:
http://en.wikipedia.org/wiki/NP0
Polystyrene capacitors also share similar properties with regard to temperature stability. Ceramic capacitors are classed with regard to this and other properties, into three main classes (also known as low, mid and high k).
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OK, cool. Thanks. So I guess when buying ceramic capacitors C0G/NP0 are generally the ones one should get? |
Since they are generally not that much more, I'd recommend it - like buying 1% metal film resistors rather than carbon. You can use them in most (if not all) applications then. The only time I usually buy other than C0G ceramic ML is in the case of decoupling caps (usually 0.1uF).
Ah, those were even better value than the lot I looked at! Good pickup 
Cheers
Blair
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vozs
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| Posted: Tue Nov 27, 2012 7:54 am Post subject: |
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NPO-COG beats when it comes to ppm, i advice against buying NPO/COG
from random Joe E-bay due to the difficulty to verify they really are COG's
even if seller provide papers and swears to/by the almighty supremebeing.
A plastic bag of ceramics can be any Chinese ceramics crap, besides
NPO-COG's is cheap enough at the bigh elephants, Mouser DIGI, Farnell. 
For your own DIY sanity notify the resistor crap scam in another Muff thread. |
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Dr. Sketch-n-Etch
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| Posted: Tue Nov 27, 2012 12:07 pm Post subject: |
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| frijitz wrote: | | Dr. Sketch-n-Etch wrote: | | I have never used polystyrene caps personally, but I have found that polypropylene film caps (I prefer the WIMA ones which look like little red bricks) work very well for filters. A filter will self-oscillate very robustly with these, and may not with the equivalent value C0G ceramics. Indeed, I can often fix an errant filter simply by replacing the caps with WIMA PPE films. |
Yes, very low dielectric absorption. But what is their temp coeff?
Ian |
-200 ppm/deg C.
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Dr. Sketch-n-Etch
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| Posted: Tue Nov 27, 2012 12:13 pm Post subject: |
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| vozs wrote: | NPO-COG beats when it comes to ppm, i advice against buying NPO/COG
from random Joe E-bay due to the difficulty to verify they really are COG's
even if seller provide papers and swears to/by the almighty supremebeing. |
I used to have access to Epcos C0G caps very cheaply, but they stopped making them. They are bright blue with very legible labelling in white. I love those damn things (I still have a bunch of them) and I really wish I knew why they stopped making them.
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J3RK
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| Posted: Tue Nov 27, 2012 1:28 pm Post subject: |
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| Dr. Sketch-n-Etch wrote: | | vozs wrote: | NPO-COG beats when it comes to ppm, i advice against buying NPO/COG
from random Joe E-bay due to the difficulty to verify they really are COG's
even if seller provide papers and swears to/by the almighty supremebeing. |
I used to have access to Epcos C0G caps very cheaply, but they stopped making them. They are bright blue with very legible labelling in white. I love those damn things (I still have a bunch of them) and I really wish I knew why they stopped making them. |
TDK sells MLCC NP0/C0G caps for fairly decent prices. These are the ones I use: http://www.mouser.com/Passive-Components/Capacitors/Ceramic-Capacitors /Multilayer-Ceramic-Capacitors-MLCC-Leaded/_/N-4gzxj?P=1yzt48a&Keywor d=tdk&FS=True |
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negativspace
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| Posted: Tue Nov 27, 2012 1:33 pm Post subject: |
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I primarily use those TDKs as well, and I do buy C0G for all my ceramics except for 100nF decouplers. If you ever have to dive into the bin for a project it's nice to know that everything in there is sufficient for whatever job...
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vozs
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| Posted: Tue Nov 27, 2012 1:52 pm Post subject: |
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| Dr. Sketch-n-Etch wrote: | | They are bright blue with very legible labelling in white. I love those damn things (I still have a bunch of them) and I really wish I knew why they stopped making them. |
I meant SMT types, they tend to look the same more or less.
http://www.avx.com/docs/Catalogs/ccog.pdf |
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consumed
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| Posted: Tue Nov 27, 2012 2:55 pm Post subject: |
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| ringstone wrote: | | roglok wrote: | | OK, cool. Thanks. So I guess when buying ceramic capacitors C0G/NP0 are generally the ones one should get? |
Since they are generally not that much more, I'd recommend it - like buying 1% metal film resistors rather than carbon. You can use them in most (if not all) applications then. The only time I usually buy other than C0G ceramic ML is in the case of decoupling caps (usually 0.1uF). |
this has mostly been my fallback "safe" position on buying caps too. however, i switched to film box caps for decoupling for ease of repositioning (getting tired of burning my fingertips with the mlcc caps)
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