METALIZED POLYPROPYLENE FILM CAPACITOR - question

OBW0549

Joined Mar 2, 2015
3,566
This is very cool, who would have thunk... not sure if my polypro are rolled but I will try it!
If they're round, they're rolled.

It may not make much or even any difference which way they're installed, though. Back in the vacuum tube days, circuit impedances were usually a lot higher than they are today, and it was much easier to pick up noise/interference through the outer foil of a capacitor (film or metallized paper) if it was connected the "wrong" way. I'm not sure it's as much a factor nowadays.

I have a couple of very, VERY old film capacitors; they have bars on one end. None of the more modern ones in my stockpile are so marked.
 
The "outer foil" thing is new to me. How was the orientation shown on a schematic?
I tried to locate an old schematic and I don;t think they are marked on the schematic. Usually there is a pictorial view and it could be marked there.

Mr. Carlson, I believe says that the outer foil should be at the low impedance side of the circuit which makes sense.
 

bob2

Joined Jun 15, 2019
213
Hi
Has anyone tried to compare the characteristics of two capacitors with a capacity of 1uF using an RLC meter? For example, ceramic and polypropylene.
 

Delta Prime

Joined Nov 15, 2019
1,326
Plastic film capacitors can use a variety of dielectrics. Polycarbonate, polyester and polystyrene are some of the most common. Each has its own properties, allowing them to be used in specific applications. Their values may range anywhere from several picofarads to a few microfarads dependent upon the actual type.
Normally they are non-polar. In general they are good general-purpose capacitors that may be used for a variety of purposes, although their high frequency performance is not usually as good as that of the ceramic types. Some of the more common types include
Mylar - Can introduce noise when used in applications where there is vibration.
Polycarbonate - Moderate level of loss which can increase with frequency. Very high insulation resistance.
Polyester - Moderate level of loss which can increase with frequency. Very high insulation resistance.
Polystyrene - tend to be very low loss but bulky. Have a temperature coefficient of around -150 ppm / C
 

kubeek

Joined Sep 20, 2005
5,772
Has anyone tried to compare the characteristics of two capacitors with a capacity of 1uF using an RLC meter? For example, ceramic and polypropylene.
I have not tried, but I sure have the means to do it, as far as this lcr meter goes https://www.hioki.com/en/products/detail/?product_key=5824 (I have not read the manual yet, but I know it can do miracles). If we can agree on a few samples from farnell.com or tme.eu then I can order them and do some measurements, also with DC bias included.
But not really right now, I would imagine about a month to six weeks before we will be allowed back to our offices and labs.
 
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