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Old 9th April 2012, 03:41 PM   #1
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Default film dielectric capacitor rated life specifications

I've been looking for a film dielectric capacitor over 63 V rated and .015 uf. The selection of parts I get back from Newark includes a number of Vishay parts, , a CDE, and a Xicor @ 1% of the price of the others. The rated lives on the Vishay parts are 500-1000 hours at either 85 C or 105 C. I'm getting better than that, as do the people that put Vishay 715's instead of paper Mallory caps on the tone generators of their Hammond A/B/C/D/M models.
In the half ton of late 1960's electronics I own, I've never had a film dielectric cap fail. Whereas nearly 100% of over twenty year old electrolytic caps have ****y performance. I've gotten in the habit of buying e-caps with life ratings of 3000-10000 hours in the hope that I won't have to replace them 3 time for low power as I have done the B+ caps on my dynakit equipment over its 50 year life. Why are these numbers so bad, compared to the actual life of the caps I have? Is temperature such a factor that 20 degrees down give 400 times the life or something? Look at 225P15394XD3 - VISHAY SPRAGUE - CAPACITOR POLY FILM 0.015UF, 400V | Newark 500 hours @ 85 deg C. polyester film. or 715P15356KD3 - VISHAY SPRAGUE - CAPACITOR PP FILM 0.015UF, 600V | Newark polyprophylene filme 500 hours. or CDE 940C30S15K-F - CORNELL DUBILIER - CAPACITOR PP FILM 0.015UF, 3KV | Newark polyprophylene 2000 hours @85 What is different about the Epcos part? B32529C153J - EPCOS - CAPACITOR POLY FILM 0.015UF, 63V | Newark 200000 hours @ 40 deg C for a $.09 capacitor? Is temperature that big a deal on plastic, or voltage, or both? Should I cram in 600 V rated caps in place of the 50V grain of rice I'm replacing? I put a couple of Arco brand film caps for the .47 uf grid couplers on one side of my ST70 in 1975, and ran it so many hours I wore out an entire set of rectifier and output tubes and B+ cap in Houston with very little air-conditioning, and the Arco's are still fine. The Goodall brand film caps in my 1964 and 1968 Hammond organs are fine, even in the power chassis sealed up with two 5AR4 heaters over top of them. Yet the original 1968 e-caps, even the ones up on the back of the keyboard of the organs feet away from any tube, universally sounded terrible until I replaced them.
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Last edited by indianajo; 9th April 2012 at 03:48 PM.
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Old 10th April 2012, 04:53 PM   #2
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Strange, film caps don't have a wear out mechanism. They are vulnerable to over-voltage surges and high humidity, but otherwise last indefinitely.
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Old 10th April 2012, 05:07 PM   #3
Elvee is offline Elvee  Belgium
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Look at the conditions, that's pretty standard stuff:

Quote:
DC Life Test:
Capacitance are capable of withstanding a 500 hour life test
at + 85 °C at 150 % of rated working voltage. After test,
capacitance shall not have changed by more than 5 % of
initial value, insulation resistance shall not have decreased
by more than 50 % of the initial limit and dissipation factor
shall not have increased to more than 1 %.
If you use them more reasonably, and/or you tolerate a larger than 5% variation, they will last longer.
If you use them in low voltage circuits, they will last almost forever, since the life is exponentially related to the applied voltage.
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