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In Reply to: RE: Metallized caps require significant break-in time... posted by Eli Duttman on March 27, 2017 at 14:27:21
No, I don't limit current. I thought that was the point of breaking a capacitor in via this method. The rapid cycles heat the capacitor slightly. Why should being placed across 120V AC mains be harmful to a 600V capacitor -- unless it's very large?
Leslie amps use 0.1uF 600V capacitors for arc suppression in the 120VAC motor switching, and orange drops last for decades in that application.
I believe one has to approach cap ratings with caution when the cap is going across the AC line. Depending on mfgr, a cap rated for 600/630VDC may have a very much lower AC line rating. If the cap is designed for across the line use it will almost always carry a specific AC rating and an "X" designation. As I understand it, the problem with AC line ratings is that while the nominal voltage may be 120VAC, there can be multi-KV spikes due to switching of inductive loads and other events. X/Y caps are designed to deal with these events and also have a defined (safe) failure mode.
I'm not aware of any audio grade cap carrying an X or Y rating and so would be inclined to use some form of current limiting during an across-the-line break-in process such as a properly rated fuse or even an incandescent bulb matching line voltage.
I believe one has to approach cap ratings with caution when the cap is going across the AC line. Depending on mfgr, a cap rated for 600/630VDC may have a very much lower AC line rating.
I have actually seen those caps with a 1.2kv rating,mainly because of AC spikes.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
One does have to approach capacitor ratings with caution, but I am a professional amp tech with years of experience at this. Yes, capacitors do have different DC and AC voltage ratings, ratings that are usually noted on the datasheet. For example, most 1600 to 2000V DC rated capacitors are only rated 500 to 700VAC, but it's not a linear relationship. As the DC voltage ratings go up, the AC ratings plateau.
You frequently find 600V polyester film capacitors installed in guitar amps as "death caps." They could easily end up across the AC line, depending on how the ground switch was set or how the amp was plugged in. And some amps have capacitors across the output tubes plates in parallel with the output transformer. Those can see very high AC voltage swings.
For reference, both the 400VDC and 600VDC 716P types have a 200V RMS frequency-dependent AC rating. The rating starts to decrease around 12kHz, but at lower frequencies like 60Hz, the full rating applies.
...as a pro, you already know of cap rating idiosyncrasies and what might happen if not heeded. And that if used, a "death cap" should carry a type "Y" rating.
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