lkipod

Polystyrene Capacitors sensitivity
« on: March 13, 2017, 10:19:44 PM »
Hi fellows,

I made a little experiment, because I wanted to find out, to which extend the precautions regarding styroflex caps must be met.
Often it is said that polystyrene caps are uber sensitive to heat and to Isopropanol.

So I took a NOS Siemens 10nf 160V polystyrene capacitor and connected it to a 60000 count multimeter and measured 9.672nf.

While still connected I rubbed 99% IPA on it - only very little changes in capacity, I assume because of the alcohol still on the cap.
After it dried it moved back to 9.672nf.

Then I dunked the cap in alcohol and left it to sit there 5 minutes. When I came back and took the cap out of the Ipa the capacitance moved back to 9.672nf.

The next test was the heat test. I put my iron at 330 degrees Celsius and started to heat the lead wire of the cap next to the body.
Immediately the capacitance started to rise up to 10.03nf, after ca. 10 seconds I let the cap cool down. Contrary to what I heard before, the capacitance went back to original after the cap had cooled down. I repeated this test several times with the same outcome.
Then I heated the cap continuously until it started to melt where the wire connects to the body, capacitance now was at 10.4nf.
Even after this extreme heating (ca. 20 seconds) the capacitance went back down, but not to the original value, instead it halted at 9.880nf.

I think I'm going to repeat this test with another brand capacitor, but for now my conclusion is that I was far too afraid regarding the use of alcohol near the polystyrene caps.
Regarding heat, one should be careful but if the heating is in normal timespan of a few seconds nothing bad happens.

What do you guys say?
Did I totally mess this up?  ::)
Or are the results somewhat reliable?

I'm waiting for your responses :D

Cheers
Moshe


Re: Polystyrene Capacitors sensitivity
« Reply #1 on: March 14, 2017, 01:36:58 AM »
I'll add that I burnt a corner of one of my polysyrene caps off by accident (soldering iron touched it). The foil is not exposed to the air at the burnt corner.

There does not appear to be any difference in capacitance. I do not expect there to be any difference until the foil is exposed to the air OR the polystyrene between the foil rolls is melted.

TLRT

Re: Polystyrene Capacitors sensitivity
« Reply #2 on: March 14, 2017, 06:26:24 AM »
Styros are self-healing ,but check the leakage after this test:) For mic filtering position it is really important to have no leakage.

lkipod

Re: Polystyrene Capacitors sensitivity
« Reply #3 on: March 14, 2017, 10:58:31 AM »
Styros are self-healing ,but check the leakage after this test:) For mic filtering position it is really important to have no leakage.

How would I check the leakage?
I suppose my DVM doesn't suffice? :P

TLRT

Re: Polystyrene Capacitors sensitivity
« Reply #4 on: March 14, 2017, 01:05:20 PM »
Better LCR meters have this function,I have DER EE DE-5000, this tool saved a lot of time for me when restoring old tube mics...

lkipod

Re: Polystyrene Capacitors sensitivity
« Reply #5 on: March 14, 2017, 02:30:51 PM »
Better LCR meters have this function,I have DER EE DE-5000, this tool saved a lot of time for me when restoring old tube mics...

Yeah I suppose that is not in my budget right now, even if I like these toys  ;)

I did a leakage test as supposed in this article, http://www.angelfire.com/electronic/funwithtubes/Testing_caps.html

According to this test the abused and a new polystyrene caps perform alike...

What is your opinion on that test?


TLRT

Re: Polystyrene Capacitors sensitivity
« Reply #6 on: March 14, 2017, 04:38:27 PM »
Yeah I suppose that is not in my budget right now, even if I like these toys  ;)

I did a leakage test as supposed in this article, http://www.angelfire.com/electronic/funwithtubes/Testing_caps.html

According to this test the abused and a new polystyrene caps perform alike...

What is your opinion on that test?

This is for electrolytics,  stryo caps have leakage in the Mohm ranges, my last example was an vintage AKG C12, styro had a leakage around 150Mohm, mic was fully restored but sounded really bad because of that filter cap...

lkipod

Re: Polystyrene Capacitors sensitivity
« Reply #7 on: March 15, 2017, 09:37:14 AM »
Interesting!
So what would a normal leakage resistance be for a Styroflex type? (I suppose the perfect capacitor should not leak at all)

TLRT

Re: Polystyrene Capacitors sensitivity
« Reply #8 on: March 15, 2017, 10:45:38 AM »
Interesting!
So what would a normal leakage resistance be for a Styroflex type? (I suppose the perfect capacitor should not leak at all)

The "normal" is the no leakage at all:)

Re: Polystyrene Capacitors sensitivity
« Reply #9 on: March 08, 2020, 09:31:40 PM »
How sensitive are polystyrene to alcohol. I've tried my best to clean around them without getting any on it, but I'm sure I got a at least a little on it.

Ryan