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 Post subject: really old 4700uF capacitors
PostPosted: Sun Dec 31, 2017 9:56 am 

Joined: Fri May 10, 2013 12:55 pm
Posts: 31
I found a case of common electrolytic capacitors that I left unused for 30 years.
Seems to still work. I found one that heats up. But the rest seem to still work.

I'm reading about how capacitors have a shelf life of 3 years. How can this be?
https://www.google.com/search?source=hp ... oKJaa72yRg

When I was a boy, I built a power supply using a transformer, two 4700 uF capacitors, and a LM317 - as typical. It still works. I can't imagine de-soldering capacitors every 3 years.


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 Post subject: Re: really old 4700uF capacitors
PostPosted: Sun Dec 31, 2017 4:42 pm 
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Location: NewJersey
solar3000 wrote:
I found a case of common electrolytic capacitors that I left unused for 30 years.
Seems to still work. I found one that heats up. But the rest seem to still work.

I'm reading about how capacitors have a shelf life of 3 years. How can this be?
https://www.google.com/search?source=hp ... oKJaa72yRg

When I was a boy, I built a power supply using a transformer, two 4700 uF capacitors, and a LM317 - as typical. It still works. I can't imagine de-soldering capacitors every 3 years.


Hello there,

Old electrolytic capacitors that have not been used for years are supposed to be "formed" by increasing the voltage across them slowly. I have never had a chance to test this theory though as i either just used mine or threw them out. Obviously this is much more important with the higher voltage ones like 100v and above. You dont want one to explode on you or it could be bad, and makes a mess at best.
Always wear eye protection. I've seen some large ones blow up like dynamite.



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 Post subject: Re: really old 4700uF capacitors
PostPosted: Sun Dec 31, 2017 11:45 pm 
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Joined: Sat Nov 08, 2003 1:01 am
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Location: Phoenixville, PA USA
AFAIK, that shelf life refers to sitting unused before any drying or deterioration of electrolyte may occur. This doesn't mean they won't be any good, it just means they MAY start exhibiting signs of degradation in one or more of a varied set of parameters: actual capacitance, voltage rating, heat rating, ESR, etc. Being in use keeps the electrolyte "fresh" via use which helps keep all other parameters in check, to a degree. Obviously these are what could be considered "wear items" and are usually the first things to suspect in faulty equipment.

What to do with the old ones you have? Start by measuring a test batch and see how close to tolerance they are. If still within tolerance, "form" them as MrAl suggests. That should bring them back / insure they are serviceable. If anything, it'll weed out the truly bad ones.
CeaSaR



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 Post subject: Re: really old 4700uF capacitors
PostPosted: Mon Jan 01, 2018 3:39 pm 
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Location: Maryland
I restored an old RCA Cathedral style radio years ago. I replaced all the capacitors with new ones.
When I fired it up, It played well but all I could get was modern music :???: .

(Don't be critical! At least it's another post...)



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 Post subject: Re: really old 4700uF capacitors
PostPosted: Mon Jan 01, 2018 6:02 pm 

Joined: Fri May 10, 2013 12:55 pm
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thanks


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 Post subject: Re: really old 4700uF capacitors
PostPosted: Tue Jan 02, 2018 9:47 am 
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Location: USA / North Carolina / Fayetteville
i'm thinking the 3 yrs thing is maybe if the item has had heavy use ?
but still i think that is BOGUS..
i have a old Telefunken and a Grundig (German tube type Radios ) that still play very well.


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 Post subject: Re: really old 4700uF capacitors
PostPosted: Tue Jan 02, 2018 12:48 pm 

Joined: Fri Aug 22, 2003 12:01 am
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Location: (somewhere), Afghanistan; from Rochester, NY
Quote:
i'm thinking the 3 yrs thing is maybe if the item has had heavy use ?
Turn that around. If they don't have any use they deform.



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 Post subject: Re: really old 4700uF capacitors
PostPosted: Wed Jan 03, 2018 10:13 pm 
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Location: Phoenixville, PA USA
Lenp wrote:
I restored an old RCA Cathedral style radio years ago. I replaced all the capacitors with new ones.
When I fired it up, It played well but all I could get was modern music :???: .

(Don't be critical! At least it's another post...)

Reverse the leads on the antenna. That way it'll reverse the radio waves and make them older. If that's not enough, reverse the leads to the speaker to enhance the antenna mod. If that doesn't work well enough, turn the cathedral upside down and face it backwards. The old stuff should be blaring out of it by now.

If that doesn't work, well, just say the radio is broken and you won't hear that modern music at all!

:) ;)


CeaSaR



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 Post subject: Re: really old 4700uF capacitors
PostPosted: Wed Jan 03, 2018 10:43 pm 
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wOW! CeaSar I never considered that antenna polarity reversing idea. I did hook it up once to a TV rabbit ears antenna and it got crackly sound from 'The Jack Benny Program'.
When I reversed the cabinet, guess what! It started talking sdrawkcab. An old county western ballad was on and,....his girlfriend came back, his junk car ran again, the half empty bottle was full, and the dog rose from its grave.
But, the good news is, when I shorted out the line cord overnight, it drained all that old stuff from them compacatators. :shock:

(If my handler sees what I write, they'll put me away AGAIN)



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 Post subject: Re: really old 4700uF capacitors
PostPosted: Thu Jan 04, 2018 8:32 am 
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^^^ :grin: :razz: :mrgreen: ^^^
Rabbit ears? I thought you might have picked up Bugs Bunny? Hehe.



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