Getting a good number of polyester capacitor lifetime

For some analogue synth stuff, I’m looking at using polyester capacitors in certain places. Looking at some of them at Mouser and Digikey, I see strange numbers for ones by CDE / Illinois Capacitor. Those are rated for 2000 hours, yet similar capacitors from, say, Kemet, are rated for longer than 200,000 hours. Maybe this is because the line in CDE/IC’s datasheets on this reads “2000 Hours, +85C with 125% of rated voltage”, whereas Kemet’s datasheets say “Operational life > 200 000 h”. How can I get a good idea of how long a CDE/IC polyester cap should last if not abused?

As a practical matter, what is the source of your concern? I think that film capacitors will generally outlast the equipment in which they are used. The only counter-example I can think of is aluminum electrolytics. Burn in tested an enclosed switching power supply at full load. The smallest electrolytic was the first components to fail. Slightly larger one followed. Aluminum electrolytics have a predictable wearout mechanism. I think that if you are conservative in your use of film capacitors, you will not see any failures. And…aren’t polypropylene capacitors better than polyester? Dielectric absorption and dissipation factor…

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Since I’m trying to replicate Moog circuits, I thought it would be best to stick with caps of the specified materials. While dielectric absorption and dissipation being better with polypropylene/mylar caps is a good reason to use that material, I’m wondering what differences there are in the resulting audio.

Do you intend to run it at 125% of rated voltage?

No. Which I suppose would mean that these caps would last indefinitely.

While it’s nice to get an idea of how long a part will last when abused, I thought it was odd that a normal lifetime wasn’t mentioned on the CDE/IC datasheets.

The “wear-out” time for a film capacitor is extremely long. Longer than any semiconductor. It’s lifetime is not what you need to worry about, it’s the electrolytics in the power supply.

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WOW is that ever a “loaded question.” When it comes to analog audio and capacitors there is an amazing amount of fanaticism about details. Copper capacitor leads. The absolute best speaker wires. The thing of it is that it is often difficult to do blind tests to prove or disprove these “lunatic fringe” theories. I am sure that others on this forum can tell you a lot more than I can.

This is the first example-link I found. I know nothing about this company:

Remember one other thing: If you turn WOW upside down, you get MOM. :slight_smile: (No that has nothing to do with the topic at hand.)

Why be so conservative?

I have some old Siemens 470 nF 400V DC “stacked film” capacitors. They are bare (not cased or conformal coated.) They are very entertaining to watch when you apply 600 - 700 VDC. I remember that they spark a lot, and maybe that they eventually disintegrate. That is great for high end audio.

Mylar is a Dupont (??) brand name for polyester. Polypropylene has the better characteristics and ought to theoretically be better somehow, but I doubt whether you can tell. Teflon ought to be very good but will require a significantly larger capacitor.

Nah, I get my kicks microwaving CDs and DVDs for 5 seconds; no HV supply needed. There is actually a use for this; for when you don’t want people reading your discarded media. But put it in a plastic bag when you do this as fumes are emitted. Sometimes I wonder why I’m not dead of industrial chemical poisoning or electrocution. :crazy_face:

That is why capacitors are better than DVDs. Dumpster divers cannot get your personal information from capacitors. (Huh, what??!!)

Would you like to wait 200 years from element being manufactured to be put on market?

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Three things govern the age of an electrolytic

  1. Temperature factor - the further you are from 25C the shorter the life
  2. Voltage factor - the closer you are to the rated voltage, the shorter the life
  3. Current factor - the higher the ripple current, the shorter the life


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Right. Somehow I temporarily got that backwards.

That’s what math is for.

Well, that’s a fun loophole! Exceed the rated voltage by 1000% and you’ve got a really long-lived capacitor!

note the power to negative number

Some years ago I saw some electrical engineer seriously saying he thought it OK to exceed voltage ratings on ceramic capacitors. I guess sometimes they may not fail. But if you ever look into capacitance versus voltage, you will see that (for example) you can get a 22 uF 25V X5R ceramic capacitor in an 0805 chip. Although it might give you about 22 uF @ 0V, it might only give you 2-3 uF at 25V. So if it does not fail catastrophically at 30V, I am sure you would get even less capacitance with that voltage applied.

I’ve some professional experience with reliability. Grossly things die according to:

  1. Power dissipation. Voltage regs, power amps (any freq). Rel predictions will almost always say ps dies first.

  2. Operating temp

  3. Over stressed: too high voltages or current. You should derate components. Use caps with a higher voltage rating than usual.

Generally I agree. But aluminum electrolytic capacitors have a predictable wearout mechanism. Higher temperature and smaller size cause faster wearout. I have confirmed this with failures of a power supply in life test, and also the control board of the old gas stove which we replaced two months ago.