METALIZED POLYPROPYLENE FILM CAPACITOR - question

Thread Starter

Wolframore

Joined Jan 21, 2019
1,748
Couple questions - I don't see polarity markings on these so I'm guessing they are fine to go both ways without issues.

I've noticed many of these have higher voltage ratings than ceramics are there other advantages and disadvantages to this type of capacitor? Where are they generally used and why?
 

MisterBill2

Joined Jan 23, 2018
6,675
Polypropylene capacitors have lower losses than ceramic ones. Each different type has properties that make it best for different applications. There have been several published discussions about the properties of the different types, unfortunately I have no links to them.
 

kubeek

Joined Sep 20, 2005
5,730
They are usually physically large, but usually have quite substantial current carrying capability. Mainly used as filtering caps in mains power supplies, snubbers etc.
 

Audioguru again

Joined Oct 21, 2019
1,727
For audio coupling:
A ceramic capacitor is microphonic which causes noises or acoustical feedback howling.
The value of a ceramic capacitor changes with the signal voltage causing distortion.
A film capacitor is larger and more expensive.
 

Analog Ground

Joined Apr 24, 2019
416
1) Film capacitors have a much lower temperature coefficient than ceramics (except NPO dielectric ceramics). The capacitance value is generally quite stable.
2) Film capacitors, except "non-inductive" types, will generally have inductance which reduces use at higher frequencies.
3) Film capacitors can periodically short out at extreme conditions but "self heal" when they rapidly discharge through the short. This can be a problem in some applications.
4) Film capacitors are physically larger then ceramic since the dielectric constant is lower.
5) Film capacitors have much higher resistance which is where they really shine.
Edit: Forgot to mention, film caps can have very low dielectric absorption. Charge up a ceramic capacitor. Then, discharge it fully. Open up the cap and come back after awhile. There will be a voltage across it. Film caps are better for precision application like sample and holds since they have much lower dielectric absorption.

There are several common types of film capacitors. I used to use polystyrene when very high stability was required such as high stability filters and op amp integrators. I think other types may have caught up with polystyrene and they may not be that common now.
 
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Thread Starter

Wolframore

Joined Jan 21, 2019
1,748
perfect, I found a great deal on 0.1 uF and plan on using them for opamp integrators for an end of year Analog PID project... sounds like it should work. I'm using all thru hole and biggest potentiometers (with bakelite chicken heads) and old school stuff I can find. Sounds like the caps will be perfect for the integrators and differentiators! It's nice to try new things.... and I'm using physically larger components.

@Analog Ground - when you say high resistance, are you talking about ESR?.... just read this https://www.vishay.com/docs/26033/gentechinfofilm.pdf ... I guess you are refererring to insulation resistance which is why I see them rated for higher voltages than some of the others....
 

Analog Ground

Joined Apr 24, 2019
416
perfect, I found a great deal on 0.1 uF and plan on using them for opamp integrators for an end of year Analog PID project... sounds like it should work. I'm using all thru hole and biggest potentiometers (with bakelite chicken heads) and old school stuff I can find. Sounds like the caps will be perfect for the integrators and differentiators! It's nice to try new things.... and I'm using physically larger components.

@Analog Ground - when you say high resistance, are you talking about ESR?.... just read this https://www.vishay.com/docs/26033/gentechinfofilm.pdf ... I guess you are refererring to insulation resistance which is why I see them rated for higher voltages than some of the others....
Yes, I am referring to insulation resistance. They will be much better for integrators. I have a short story about ceramics and integrators. In my first job, I built a prototype with a ceramic feedback capacitor. As the output ramped up with a constant DC input, the ramp did all kinds of dipsy doodles on the way to full scale. "What is going on?" As the voltage increased across the capacitor, the capacitance was changing. Voltage Coefficient of Capacitance. I switched to polystyrene.
 

Thread Starter

Wolframore

Joined Jan 21, 2019
1,748
Does the polystyrene ones smell funny when they get too hot? Just curious if it smells like plastic.

All very good information! Thanks again...

1585253110719.png

@jpanhalt that's a nice comparison chart.

I'm aware of the ceramics resonating but I guessed that we are talking about higher frequencies than audio.... Also for ESR they are pretty good. In fact I'm pretty happy with them, they don't seem great for leakage.

1585253681687.png
 
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OBW0549

Joined Mar 2, 2015
3,503
If I recall correctly, one of the big problems with polystyrene capacitors is that they were very vulnerable to attack by board-cleaning solvents. That, and they didn't like high temperatures.
 

jpanhalt

Joined Jan 18, 2008
10,067
Yes, polystyrene as a plastic is not very stable to heat or solvents. As for solvent attacking a sealed capacitor, there are probably lots of factors to consider. They are getting hard to find too.
 
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