Questionable Capacitor-How to Identify this one?

[Xnke]

Early last year, I bought a capacitor bank and diode bridge at the hamfest, purely because it was very inexpensive and was rated at 2.5KV. Just got it out and started cleaning it off, and noticed that one capacitor looked a bit different.



The top and bottom of the can are bulged out.





The other two capacitors in the bank were not like this, the cans weren't damaged or distorted so I went ahead and trimmed the phenolic spacers down to get rid of a big crack in one, which removed one slot for a cap to go in.

But, it got me thinking-are these capacitors electrolytics, or oil capacitors? They're big enough to be either. The voltage rating had me convinced they were oil-types when I bough them, but the swelled can makes me think maybe not.

All three capacitors measure 36-37uF on the LCR meter, and the huge diode bridge they were hooked to checked out fine as well. It's just the bulged out can has me a bit worried about using that third one.

[bob91343]

Electrolytic capacitors are not available in such high voltage.  The highest I remember from the old days is maybe 600V but typically nothing above 475 V.

The bulge indicates overheating in the past, the oil inside having gotten very hot.  This implies a bad capacitor and I'd throw that one away.

[T3sl4co1l]

That, or internal arcing, which also generates gas (which may still be present -- treat it as a pressure vessel just in case).

I have some caps which are advertised as having a gas fuse, for lack of a better term:
The overall construction is a film-foil roll, impregnated with oil, and connected with two foil tabs roughly in the middle of the roll.
The enclosure/can is made with a double rim, crushed to almost no height; this rim expands heightwise, like a bellows, when internal pressure develops.
The foil tabs are made just long enough to reach the terminals.
If the top expands off the body due to internal pressure expanding the crushed rim, the foil tabs are pulled off, breaking the current path.

It would appear yours was not constructed in this way (despite the amount of expansion the top has gone through!)...

Definitely replace it, perhaps all of them if possible.  Heh, hmm, won't be cheap...

Tim

[Gyro]

The 'MP' implies metallised paper... and the hermetic sealing and voltage rating, oil filled. Hopefully enough to prevent them from performing the Rifa party trick!

[radiolistener]

it looks like oil. Note that oil used in such capacitors is very-very toxic poison, don't try to disassemble it at home

[T3sl4co1l]

it looks like oil. Note that oil used in such capacitors is very-very toxic poison, don't try to disassemble it at home

It doesn't say "Made in E/W Germany", it's not that old...

Tim

[Gyro]

January 1981?

[Quarlo Klobrigney]

See: Pyranol and its nasty effects. Used by GE and manufactured by Monsanto We Hams knew about this stuff leaking out of transformers and capacitors back in the late 70's.

Quote from: radiolistener on 2020-07-25, 05:49:20

it looks like oil. Note that oil used in such capacitors is very-very toxic poison, don't try to disassemble it at home