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Old 24th December 2012, 03:41 PM   #21
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Quote:
Originally Posted by jcx View Post
its continuous DC bias at higher V that stresses dielectric

if "toughness" is just surviving seconds of transients then its no indication

Higher DC fields drive different degradation/breakdown phenomena to penetrate a dielectric over time - opto isolator WVDC ratings are lots lower than the 1, 60 sec withstand test V because of this


I'm suspicious that maybe the datasheet writers are just doing the AC Vpk math - and may have never tested at 1000s of hrs with DC bias
Ok but I do'nt see the opto isolator correlation to polyprop motor caps. Please go on . As for the 1000s of hours of test would years of use over the rating suffice or is there some other lab rating that will do ? The stress of dc bias and resulting failure is not to be taken lightly some examples of such would help there should be from the manufactures web sites. Regards
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Old 24th December 2012, 04:37 PM   #22
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"Motor caps" rated at a certain AC voltage must withstand shutoff transients of 6 to 10 times running voltage. That is what motors put out if not transient suppressed. If you put a scope in a factory AC line, that is what you will see. So that sort of explains why film motor caps are so huge. I imagine the 1000 VDC rating of my 500 VAC genilec caps in my organ is very conservative. I don't expect to ever replace them, not at the current a 5AR can deliver to them. Heat is one thing that really kllls plastic film. Won't get much of that in hifi service, unless the mounting postition is wrong.
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