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Old 19th September 2009, 03:48 PM   #1
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Default Polyester or Polypropyolene. Which is which?

I have a quantity of the caps shown in the photo below. Some are polyester and some are polypropylene but I cannot remember which is which.

Caps numbered 1, 4 and 5 look like polypropylenes, with the rest being polyester.

Can someone confirm this or correct me?

How does one differentiate the two types of caps?

Many thanks.
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Old 20th September 2009, 11:58 PM   #2
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No answers? Was this a stupid question?
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Old 21st September 2009, 01:15 AM   #3
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Originally Posted by Black Gate View Post
No answers? Was this a stupid question?
No, it isn't a stupid question. You'll need a really great impedance meter like an HP or Gen Rad to measure both the impedance and dissipation factor.
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Old 21st September 2009, 01:52 AM   #4
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You can make some educated guesses...

Polyprop caps are generally larger for a given value. For example, the 2.2uF is definitely a polyester cap.
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Old 21st September 2009, 07:49 AM   #5
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Oh well, thanks anyway guys. Cheers!
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Old 21st September 2009, 08:16 AM   #6
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Yea I dont think you can really tell from the outside. As Jack said you need a descent Impedence meter to determine that.
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Old 4th October 2009, 05:41 AM   #7
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The quick and dirty test I use for capacitors is to charge the unit to, say 10 volts, then short the terminals for several seconds, wait a minute and then measure the remaining voltage with a high-impedance voltmeter. Polypropylenes will have a significantly lower residual voltage, though measuring lower-capacitance units gets tricky.
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Old 4th October 2009, 06:04 AM   #8
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Quote:
Originally Posted by Black Gate View Post
No answers? Was this a stupid question?

This has been discussed before and is really fast and simple. Polyester has a positive tempco and polyprop negative. Use a hair dryer and capacitance meter and you'll have the answer in seconds.
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Old 4th October 2009, 12:16 PM   #9
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This has been discussed before and is really fast and simple. Polyester has a positive tempco and polyprop negative. Use a hair dryer and capacitance meter and you'll have the answer in seconds.
Nice trick, I didn't know that! My method, much less elegant, is to destroy one, unwind a bit, then ignite with a cigarette lighter. PP smells like a burning candle, PE smells slightly sweetish.
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Old 4th October 2009, 12:20 PM   #10
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My trick is to not worry about it.

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