HI all.
I am aware that the usual life span of electrolytics, subject to use is in the order of 15 years, give or take.
My question is, do film capacitors eg, polystyrene, polyproplyne etc suffer the same fate?
I ask this beceause a still have good stocks of Rifa / ROE / WIMA etc which have never been used, but are approaching 15 years old.
If any one can help me with this question it will be greatly appreciated.
It seems a shame to have to throw them out, but if they are no good beceause of age, Oh well!!
Regards,
George.
I am aware that the usual life span of electrolytics, subject to use is in the order of 15 years, give or take.
My question is, do film capacitors eg, polystyrene, polyproplyne etc suffer the same fate?
I ask this beceause a still have good stocks of Rifa / ROE / WIMA etc which have never been used, but are approaching 15 years old.
If any one can help me with this question it will be greatly appreciated.
It seems a shame to have to throw them out, but if they are no good beceause of age, Oh well!!
Regards,
George.
If there's no unusual amounts of ozone, heat, or UV (i.e., they're tucked away somewhere in a box), they'll be fine, probably good as new. Unlike paper, polystyrene and polypropylene are hydrophobic (don't pick up moisture).
I've seen some polyester caps deteriorate, but they were exposed to some pretty bad conditions of heat cycling and extreme humidity, and polyester is hygroscopic for a film (don't remember exactly, but something like 1-1.5% moisture pickup), though still not very hygroscopic. Never had a stored polypropylene or polystyrene go bad, and I've got plenty that are 20 years old and more.
I've seen some polyester caps deteriorate, but they were exposed to some pretty bad conditions of heat cycling and extreme humidity, and polyester is hygroscopic for a film (don't remember exactly, but something like 1-1.5% moisture pickup), though still not very hygroscopic. Never had a stored polypropylene or polystyrene go bad, and I've got plenty that are 20 years old and more.
Hi Sy.
Thank you very much for that.
I would have been a shame to have to throw them out.
I must admit, I have been using them continuously since i got them, and they "appear" to work fine.
However they generally have not been used in any precision electronic work or high quality audio work, so if they were not 100%, I probably would not have been able to tell.
I got lucky a long time ago, when a local distributor was closing down, and everything was going for a song.
With regards to storage, they have not been exposed to humidity, or any regular temp changes.
I feel more confident now to use them in my x/ono preamp.
Once again thanks for your response.
Regards,
George.
Thank you very much for that.
I would have been a shame to have to throw them out.
I must admit, I have been using them continuously since i got them, and they "appear" to work fine.
However they generally have not been used in any precision electronic work or high quality audio work, so if they were not 100%, I probably would not have been able to tell.
I got lucky a long time ago, when a local distributor was closing down, and everything was going for a song.
With regards to storage, they have not been exposed to humidity, or any regular temp changes.
I feel more confident now to use them in my x/ono preamp.
Once again thanks for your response.
Regards,
George.
No, metallized polyester have a much longer lifespan than electrolytics as they contain no liquid electrolyte to dry out. In use they might fail if subjected to pulse stress - they're not to be used across the mains supply for example unless specified for that application. Some types though are self-healing and can withstand a certain degree of abuse.
People don't change "red caps" (mallory plastic film) in Hammond organs, and they started using those about 1965. They went bankrupt about 1974. One L model was recently reported rescued from the alley behind a bar in Juneau, AK, where the bar owner said it had been sitting for 3 years. After oiling and a little TLC, an organforum member said It still worked. It's getting a case replacement. Some of us do change all the electrolytics, however. The paper caps used before the red ones deteriorate in a way that some people find mellow in tone and others replace for more highs.
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The life of Electrolytic caps will vary hugely according to use. In a hot environment and with high ripple current I have known them to fail in a few months. Conversely I have an AVO Oscillator made around 1939. The HT smoothing cap failed around 1975 and I replaced with a NOS cap dated 1951. It is still working fine.
Barry
Barry
Many paper capacitors tend to age in a disgraceful manner.
But the OP's question is about film capacitors. In general, they fare much better.
I have noted some exceptions however: some early metalized polyester and polycarbonate caps from some manufacturers (Hunts in particular) seem to suffer from a form of contamination, and show severely degraded performances after 40 or 50 years.
Plain foil types seem more robust: I have very early models of styroflex caps of the 50's still in a very good shape.
Film capacitors made by reliable manufacturers after the late sixties should normally be, and remain in an excellent condition.
I have made a number or tan delta tests corroborating this: it is one of the key parameter for evaluating the degradation of a film cap;
See here:
http://www.diyaudio.com/forums/part...ouve-never-heard-post2026949.html#post2026949
http://www.diyaudio.com/forums/part...ouve-never-heard-post2020859.html#post2020859
http://www.diyaudio.com/forums/part...ouve-never-heard-post2020208.html#post2020208
http://www.diyaudio.com/forums/part...ouve-never-heard-post2020123.html#post2020123
http://www.diyaudio.com/forums/part...ouve-never-heard-post2027902.html#post2027902
http://www.diyaudio.com/forums/part...ouve-never-heard-post2029904.html#post2029904
http://www.diyaudio.com/forums/part...ouve-never-heard-post2037625.html#post2037625
But the OP's question is about film capacitors. In general, they fare much better.
I have noted some exceptions however: some early metalized polyester and polycarbonate caps from some manufacturers (Hunts in particular) seem to suffer from a form of contamination, and show severely degraded performances after 40 or 50 years.
Plain foil types seem more robust: I have very early models of styroflex caps of the 50's still in a very good shape.
Film capacitors made by reliable manufacturers after the late sixties should normally be, and remain in an excellent condition.
I have made a number or tan delta tests corroborating this: it is one of the key parameter for evaluating the degradation of a film cap;
See here:
http://www.diyaudio.com/forums/part...ouve-never-heard-post2026949.html#post2026949
http://www.diyaudio.com/forums/part...ouve-never-heard-post2020859.html#post2020859
http://www.diyaudio.com/forums/part...ouve-never-heard-post2020208.html#post2020208
http://www.diyaudio.com/forums/part...ouve-never-heard-post2020123.html#post2020123
http://www.diyaudio.com/forums/part...ouve-never-heard-post2027902.html#post2027902
http://www.diyaudio.com/forums/part...ouve-never-heard-post2029904.html#post2029904
http://www.diyaudio.com/forums/part...ouve-never-heard-post2037625.html#post2037625
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You can identify a film cap dielectric by testing its dielectric absorption. You can do this in the field with a 9V battery and a basic DMM. Charge the cap by connecting it across the battery for 10 seconds, take the battery off, short the cap leads for exactly one second and then measure the voltage that appears across the cap using a high input impedance voltmeter - a modern el-cheapo 3.5 digit DMM in voltage mode is fine. Try not to touch both leads when measuring the recovery voltage - you don't want to drain off any of the recovery charge and affect the voltage reading.
The recovery voltage is not dependent on the value of the cap, only the dielectric. It's a percentage of the applied voltage, and depends only upon the dielectric composition. You'll have to get some samples of various capacitors with known dielectrics like mylar, polypropylene, polystyrene, polycarbonate, teflon etc. and apply this measurement procedure repeatably to get a set of numbers that correspond with these dielectrics. The recovery voltages are on the order of 1-10 millivolts with a 9V battery and this basic procedure. Some of the higher performing dielectrics like teflon, polystyrene and polypropylene might be hard to distinguish among, since their dielectric absorption is so low. However, polycarbonate will be a good bit higher, and mylar will be a good bit higher than mylar, so you can distinguish among the "good" dielectrics and the lesser dielectrics pretty reliably.
I've used this procedure at flea markets to determine whether to buy a box of caps or not, and it's been very useful and reasonably reliable if your procedure is consistent. It's also non-destructive, so you could easily test the parts you have and then re-use them.
The recovery voltage is not dependent on the value of the cap, only the dielectric. It's a percentage of the applied voltage, and depends only upon the dielectric composition. You'll have to get some samples of various capacitors with known dielectrics like mylar, polypropylene, polystyrene, polycarbonate, teflon etc. and apply this measurement procedure repeatably to get a set of numbers that correspond with these dielectrics. The recovery voltages are on the order of 1-10 millivolts with a 9V battery and this basic procedure. Some of the higher performing dielectrics like teflon, polystyrene and polypropylene might be hard to distinguish among, since their dielectric absorption is so low. However, polycarbonate will be a good bit higher, and mylar will be a good bit higher than mylar, so you can distinguish among the "good" dielectrics and the lesser dielectrics pretty reliably.
I've used this procedure at flea markets to determine whether to buy a box of caps or not, and it's been very useful and reasonably reliable if your procedure is consistent. It's also non-destructive, so you could easily test the parts you have and then re-use them.
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