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Questionable Capacitor-How to Identify this one?




 
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Author Topic: Questionable Capacitor-How to Identify this one?  (Read 576 times)
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KI4YAN
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« on: July 22, 2020, 06:16:42 PM »

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.
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K1JJ
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« Reply #1 on: July 22, 2020, 07:37:31 PM »

It's either an old German WWII hand grenade or a can of German beer.   Notice the "Made in Germany."

But seriously, the bulge is like a rattlesnake warning you to stay clear if you put any voltage on it.

T
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KI4YAN
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« Reply #2 on: July 22, 2020, 09:05:13 PM »

That's what I figured. I did find out, these are Siemens paper-in-oil capacitors. The two that aren't bulged out got proofed at 2.5kV DC for about an hour tonight, didn't even get warm. One of the local RF engineers is bored with working from home due to Covid, so allowed me to come into the lab he works at and use the BIG variac. I brought the 2500V plate transformer and the diode bridge that came with these capacitors, and we loaded it with a 500mA load for two hours.

The two caps didn't get hot, the transformer got up to 120F, and the diodes got a little warm. Probably need a heatsink warm.

Now that I'm back home I realize I should have brought the biggest filter choke I have and actually built the power supply while I had access to the big load resistor...
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KA3EKH
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« Reply #3 on: July 23, 2020, 09:50:35 PM »

Pure speculation on my part but they look like they were from a medium to high intensity obstruction lighting system. Those systems have a Ferro resonate transformer, diode assembly and two or three capacitors like that that are charged around 1.5 kV or so and dumped across a huge flash tube. They have a transformer on the other side of the tube that generates a short duration very high voltage that starts the plasma accost the tube but the energy stored in the capacitors drives the plasma for the duration of the flash. The more capacity the brighter and longer the flash.
EG&G and Flash Technology are usually what you come across in the US so donít know about those cans. The EG&G system I use to maintain had three capacitors in it with the smallest one providing a meager four thousand foot candles in night mode, seven thousand in twilight and twenty thousand in day mode.
Also as a foot note, I worked in the broadcast industry for thirty years on AM, FM and TV transmitters and the most danger and worst shocks ever were from working on stupid high intensity obstruction lights.


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KA0HCP
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« Reply #4 on: July 24, 2020, 01:16:12 PM »

Instructions at bottom translate by machine:  "Only remove the short circuit jumper when installing"
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New callsign KA0HCP, ex-KB4QAA.  Relocated to Kansas in April 2019.
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