Non-Polar Electrolytic vs. Polypropylene Film Capacitors - Page 2 - diyAudio
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Old 19th February 2008, 03:51 PM   #11
SY is offline SY  United States
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Fixed the typo.
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Old 22nd February 2008, 01:58 AM   #12
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David, yes you can measure the voltage coefficient, and the various types are definitely different, with some ceramics being pretty easy to see. This is one reason I like my antique bridges, as they can go up to several hundred volts, unlike modern solid state bridges that are doing well to get to a couple tens of volts.

You should also measure dielectric absorption. It's sort of a PITA, with accurate timing required. I bought a computer interface with this exact thing in mind, but haven't had time to set up the experiment.

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Old 22nd February 2008, 02:11 AM   #13
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Here is a link to a reprint from Audio magazine by Walt Jung and Richard Marsh called "Picking Capacitors"
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Old 22nd February 2008, 02:16 AM   #14
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Conrad,

Your dielectric studies shifted into water absorbtion instead of charge didn't they?

How all that mess goin' anyway?

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Old 22nd February 2008, 02:20 AM   #15
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Quote:
originally posted by Conrad Hoffman
You should also measure dielectric absorption. It's sort of a PITA, with accurate timing required. I bought a computer interface with this exact thing in mind, but haven't had time to set up the experiment.

In this article by Bob Pease are described two test fixtures to measure DA:

Understand Capacitor Soakage

A simple one with a switch which has to be engaged manually and more a much more sophisticated with timers etc.
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Old 22nd February 2008, 02:30 AM   #16
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poobah, the carpet is long gone, the walls are torn out, everything is a mess, but I cleaned the seaweed and dead fish off the test bench, replaced the power strips that were under water, and at least I'm up and running! Fortunately I didn't lose much, though I did spend some time washing the components that were in the lower drawers of my parts cabinets. I also discovered you can recover some amazing things, if you act quickly. I opened up a nice dial indicator that was completely submerged, cleaned and relubed it, and it works better than new. I also have some mylar caps that were under water for a week, so I ought to check the DA on 'em! No, wait, this is 2008- just call them minty and sell them on eBay!
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Old 22nd February 2008, 02:37 AM   #17
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Thank you to all of you who provided data from personal research and those who provided links to articles and equipment.
Conrad, what is your ebay ID, I need to watch for those caps!
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Old 22nd February 2008, 03:02 AM   #18
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Thank-you and kudos on presenting some real data. Your efforts are to be applauded. As we all know, from data comes knowledge, from knowledge, wisdom.

The esr of capacitors isn't so critical because their reactance is so high at low frequency. For instance 3.3uF at 100Hz has a reactance of 482 ohms so an ohm of ESR doesn't really make much difference. Even at 10KHz, the reactance is 4.8ohms. Not to say it's not important, it needs to be taken in context and of course, it's the opposite for inductors, ESR is the essence of inductance.

As far as I know, bipolar electrolytics are formed by making a pair of double value electrolytics in series and so you'd expect their ESR and DF to be 2X worse than regular electrolytics. Let's face it electrolytics were created to do one thing well, dump lots of low frequency energy. They are not intended for audio duty.

When you give a value of <0.1ohm for instance, what do you mean? Is 0.1ohm the limit of measurement for that test condition?

I vote to make this a sticky that we should all put our data. I, for one, would really like to know if a particular manufacturer knows what they're doing!
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Old 22nd February 2008, 03:06 AM   #19
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BTW, I always thought that the reason electrolytics varied capacitance so much with frequency was due to the parasitic inductance of their construction (a coil of foil). Can anyone elucidate?
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Old 22nd February 2008, 03:30 AM   #20
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An excellent electrolytic capacitor read: http://electrochem.cwru.edu/ed/encyc...electr-cap.htm

frequency response is claimed to be roll off due to "roughness of the surface oxide," whatever that means
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