I recently bought a box of NOS electrolytics,
- Swedish ex military surplus.

They are marked 1000 uF 400V, and are
physically large 75cms in diameter and 120cms
in height.

They are also marked '92 which I took to be the
date of manufacture.

I brought them up on my psu, very slowly over 24 hrs
in case they needed to be reformed.

Two of the first batch broke down well below their
stated working voltage.

Questions:

What is the shelf life of an electrolytic?
What is the service life of an electrolytic?

What happens at breakdown?
Does the insulation between the plates puncture?

Is there any kind of self healing to allow them to
be used at a lower voltage, or...

are they (to use the technical term) "knackered" ?

Iain

Questions:

What is the shelf life of an electrolytic?

very short, especially if used, but I never would buy electrolytics that are
over a couple years old, even NOS



What is the service life of an electrolytic?

about 10-15 years if you buy brand new manufactured, made in 2004 or 2005,
otherwise who knows? 5 years? 1 year? 5 weeks? 5 hours?


PS - for sizes less than 1uF, you can safely buy NOS paper in oil,
hermetically sealed (such as vitamin Q etc.), they seem to last great on the
shelf, I have tested high quality WE, Jensen, Sprague, & Russian military
that are 50 years old and have NO measurable leakage!


cheers!

cowboy

In message , Iain M Churches
writes
I recently bought a box of NOS electrolytics,
- Swedish ex military surplus.

They are marked 1000 uF 400V, and are
physically large 75cms in diameter and 120cms
in height.

They are also marked '92 which I took to be the
date of manufacture.

I brought them up on my psu, very slowly over 24 hrs
in case they needed to be reformed.

Two of the first batch broke down well below their
stated working voltage.

Questions:

What is the shelf life of an electrolytic?
What is the service life of an electrolytic?

What happens at breakdown?
Does the insulation between the plates puncture?

Is there any kind of self healing to allow them to
be used at a lower voltage, or...

are they (to use the technical term) "knackered" ?

Iain



I'm very surprised at that. As they will be modern designs (from 1992)
then I would have thought they would all be OK. I normally check old
electrolytics by reforming them at the full voltage through a resistor
that limits the maximum leakage current to less than 10mA. If the
leakage hasn't dropped after a few hours then they're no use, but it's
not often this happens with modern devices unless they've been stored at
high temperatures. How did they break down? Very high leakage I guess.
--
Chris Morriss

physically large 75cms in diameter and 120cms
in height.

Sheesh, these are *huge*

Or did you mean 'mm'? ;-)

What is the shelf life of an electrolytic?

5 years? They need to be kept 'formed'.

What is the service life of an electrolytic?

Depends. Run at close to their max voltage rating and at high ambient
temperature could be only a year. Running well under spec at a reasonable
ambient I guess 25 years (based on electronic stuff that I'm still running
25 years on!).

Is there any kind of self healing to allow them to
be used at a lower voltage, or...

Forming.

are they (to use the technical term) "knackered" ?

How important to you is it that they function as intended? Personally I'd
just junk them, but for low impact use I might give them a go.

Al.

"Al" wrote in message
. 4...
physically large 75cms in diameter and 120cms
in height.

Sheesh, these are *huge*

Or did you mean 'mm'? ;-)

Sorry, yes. "mm" of course

Iain

"Iain M Churches" wrote

They are marked 1000 uF 400V, and are
physically large 75cms in diameter and 120cms
in height.

I assume you mean mm.

They are also marked '92 which I took to be the
date of manufacture.

I brought them up on my psu, very slowly over 24 hrs
in case they needed to be reformed.

You should limit the *current*.

Two of the first batch broke down well below their
stated working voltage.

What do you mean by "broke down"?

Questions:

What is the shelf life of an electrolytic?

Uncertain.

What is the service life of an electrolytic?

It should say in the spec. Several thousand hours usually, but
actual service will differ from test conditions so quoted life is
just a guide.

What happens at breakdown?
Does the insulation between the plates puncture?

Yes, and heat from the short eats at the foil until the oxide layer
is restored, or it makes a hole, depending on the source resistance.

There are three materials in an electrolytic cap: the metal foil,
the electrolyte which is a conductor, and the oxide layers. Areas of
missing oxide heal as long as the electrolyte is active and a
voltage of the correct polarity is applied. Small areas of missing
foil don't matter too much. Contaminated, inactive, or absent
electrolyte is a bigger problem, and that is what knackers a cap.

Is there any kind of self healing to allow them to
be used at a lower voltage, or...

Both above effects are processes of self-healing as long as current
is limited and the cap is generally sound. Otherwise they become
runaway processes of destruction because the heat generated damages
large volumes, rather than small areas.

are they (to use the technical term) "knackered" ?

Depends what you mean by "broke down". Bring them up again with a
1Meg resistor in series and see what happens. If leakage seems to
become unacceptable, reduce the voltage then wait for the current to
subside, then carry on. If you get to a point where leakage no
longer subsides after a while, the cap is knackered. Derating won't
help, unless you don't mind leakage and risk of future calamity.

cheers, Ian

cowboy wrote:

Questions:

What is the shelf life of an electrolytic?

very short, especially if used, but I never would buy electrolytics that are
over a couple years old, even NOS

Not necessarily so.

I bought four 1,500 uF x 450v caps made maybe 1965,
and made for university equipments.
They were not used much, and had been stored a long time.
I used two in a couple of monoblocs where they still work fine after
years of on-off use.

I have plenty of ancient electros which work fine, some 60 years old.

Its very rare i ever get an electro failure of high voltage caps.

I cannot recall ever buying a 40 year old NOS electro and found
it to go short.

Quite a few failures occur in small electros rated for low voltage.


What is the service life of an electrolytic?

about 10-15 years if you buy brand new manufactured, made in 2004 or 2005,
otherwise who knows? 5 years? 1 year? 5 weeks? 5 hours?

Maybe 70 years+ is more like it.



PS - for sizes less than 1uF, you can safely buy NOS paper in oil,
hermetically sealed (such as vitamin Q etc.), they seem to last great on the
shelf, I have tested high quality WE, Jensen, Sprague, & Russian military
that are 50 years old and have NO measurable leakage!

Paper in oil caps made in Japan and used in countless consumer
amps and receivers in the 1950s and 60s are horror stories, oil all over the
chassis,
and/or electronically leaky.
The large store I have of old ex mil-stock oilers rated at up to 2,000v are
more reliable, and are in hermetically sealed cans.

Some of theose large caps 3" in dia and 5 " long have a huge ripple current
rating...

Patrick Turner.



cheers!

cowboy

"Ian Iveson" wrote in message
. uk...
"Iain M Churches" wrote

Two of the first batch broke down well below their
stated working voltage.

What do you mean by "broke down"?

I was using a bench psu supplying 500V, to drive a
pair of KT88s, and I needed a lower secondary voltage,
of 300V at 20mA to drive the front end of the amp,
so I wired a 10k 6W from the psu, and then one of these
caps as a filter.

I brought the supply up slowly, slowly, and then as the
voltage across the cap reached 300V, there was a loud
"crack", and the psu tripped. (it does so at 500mA)

I repeated this a few times, as it seemed as though the
the break down was at a lower voltage each time.


are they (to use the technical term) "knackered" ?

Depends what you mean by "broke down". Bring them up again with a 1Meg
resistor in series and see what happens. If leakage seems to become
unacceptable, reduce the voltage then wait for the current to subside,
then carry on. If you get to a point where leakage no longer subsides
after a while, the cap is knackered. Derating won't help, unless you don't
mind leakage and risk of future calamity.

Thanks, I will try that, but I think I would be unwilling to use them
permanently installed in an amp.

Iain

"Iain M Churches" a écrit dans le message de news:
...

[ . . . ]

I was using a bench psu supplying 500V, to drive a
pair of KT88s, and I needed a lower secondary voltage,
of 300V at 20mA to drive the front end of the amp,
so I wired a 10k 6W from the psu, and then one of these
caps as a filter.

I brought the supply up slowly, slowly, and then as the
voltage across the cap reached 300V, there was a loud
"crack", and the psu tripped. (it does so at 500mA)

How could this happens ?
For the current reach 500mA in the 10k resistor, you should apply some 5KV !
What do I miss ?

Yves.

[ . . . ]
Iain

"Yves" wrote in message
...

"Iain M Churches" a écrit dans le message de news:
...

I brought the supply up slowly, slowly, and then as the
voltage across the cap reached 300V, there was a loud
"crack", and the psu tripped. (it does so at 500mA)

How could this happens ?
For the current reach 500mA in the 10k resistor, you should apply some 5KV
!
What do I miss ?

Yves.

I can only think that the breakdown within the capacitor caused it to
draw a large current, in excess of 500mA to ground which tripped the
sensor on the psu.

Iain

On Mon, 21 Mar 2005 12:26:14 +0200, "Iain M Churches"
wrote:


"Yves" wrote in message
. ..

"Iain M Churches" a écrit dans le message de news:
...

I brought the supply up slowly, slowly, and then as the
voltage across the cap reached 300V, there was a loud
"crack", and the psu tripped. (it does so at 500mA)

How could this happens ?
For the current reach 500mA in the 10k resistor, you should apply some 5KV
!
What do I miss ?

Yves.

I can only think that the breakdown within the capacitor caused it to
draw a large current, in excess of 500mA to ground which tripped the
sensor on the psu.

Frankie's point was that even if the cap was a dead short, a 10k
resistor connected from ground to 300 volts will only draw 30mA.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Stewart Pinkerton" wrote in message
...
Frankie's point was that even if the cap was a dead short, a 10k
resistor connected from ground to 300 volts will only draw 30mA.

Hmm. Yes. The top end of the resistor was connected to the
psu at 500VDC, but that still only makes 50mA.

So what happened?

Iain

What is the service life of an electrolytic?

about 10-15 years if you buy brand new manufactured, made in 2004 or 2005,
otherwise who knows? 5 years? 1 year? 5 weeks? 5 hours?


Maybe 70 years+ is more like it.


If it was quality to begin with. Cardboard and wax tube packaged
one (usually found in cheap AM tube radios) are almost all bad,
used or not. Aluminum can electroytics seem to last much
better.

On Mon, 21 Mar 2005 20:28:26 GMT, robert casey
wrote:

What is the service life of an electrolytic?

about 10-15 years if you buy brand new manufactured, made in 2004 or 2005,
otherwise who knows? 5 years? 1 year? 5 weeks? 5 hours?

Maybe 70 years+ is more like it.

If it was quality to begin with. Cardboard and wax tube packaged
one (usually found in cheap AM tube radios) are almost all bad,
used or not. Aluminum can electroytics seem to last much
better.

Most probably, the bottom line is indeed the original quality of
manufacture. I would expect 'computer grade' caps from the '70s to be
in reasonable condition as NOS, given careful forming, but I wouldn't
even consider the purchase of any other electrolytic capacitor more
than ten years old. The caps in my ~20 year old Krell amp are still in
excellent condition, but serious overkill is something of a byword for
this brand! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

robert casey wrote:


What is the service life of an electrolytic?

about 10-15 years if you buy brand new manufactured, made in 2004 or 2005,
otherwise who knows? 5 years? 1 year? 5 weeks? 5 hours?


Maybe 70 years+ is more like it.


If it was quality to begin with. Cardboard and wax tube packaged
one (usually found in cheap AM tube radios) are almost all bad,
used or not. Aluminum can electroytics seem to last much
better.

Nearly all the old electros i ever found are Al cans with cardboard covers.
That changed to plastic.

The nastiest, vilest, most despicable and terrifying electro
I ever met was on an old radio chassis which I had used to build a transmitter
at age 20.
There it gleefully sat, 5 inches in height, shiny Al from around 1935,
and with +500v on the AL external surface.

I went to grab the chassis, then lift it across the bench, and grabbed the
electro like the nice handle it was.

AAAAHHHHHHOOOOOOUCHHHH!!!!

The chassis somehow left a large dent in the ceiling, did a 360 on the way down,

and smashed a coupla tubes on de floor.
I somehow moved 10 feet faster than I thought possible, but at 20,
we were all indestructable, unlike the old radios we canobalised.

It was the start of a love-hate relationship with highish voltages.

I hope it don't convert to a fatal attraction.

Patrick Turner.

"Patrick Turner" wrote in message
...


cowboy wrote:

Questions:

What is the shelf life of an electrolytic?

very short, especially if used, but I never would buy electrolytics that
are
over a couple years old, even NOS

Not necessarily so.

I bought four 1,500 uF x 450v caps made maybe 1965,
and made for university equipments.
They were not used much, and had been stored a long time.
I used two in a couple of monoblocs where they still work fine after
years of on-off use.

I have plenty of ancient electros which work fine, some 60 years old.

Its very rare i ever get an electro failure of high voltage caps.

I cannot recall ever buying a 40 year old NOS electro and found
it to go short.

Quite a few failures occur in small electros rated for low voltage.


What is the service life of an electrolytic?

about 10-15 years if you buy brand new manufactured, made in 2004 or
2005,
otherwise who knows? 5 years? 1 year? 5 weeks? 5 hours?

Maybe 70 years+ is more like it.



PS - for sizes less than 1uF, you can safely buy NOS paper in oil,
hermetically sealed (such as vitamin Q etc.), they seem to last great on
the
shelf, I have tested high quality WE, Jensen, Sprague, & Russian
military
that are 50 years old and have NO measurable leakage!

Paper in oil caps made in Japan and used in countless consumer
amps and receivers in the 1950s and 60s are horror stories, oil all over
the
chassis,
and/or electronically leaky.
The large store I have of old ex mil-stock oilers rated at up to 2,000v
are
more reliable, and are in hermetically sealed cans.

Some of theose large caps 3" in dia and 5 " long have a huge ripple
current
rating...

Patrick Turner.



cheers!

cowboy


hi Patrick -
Interested in a pile (50+) of GE 45uF Dielectrol VI 500V AC (must be ~900V
DC), same 5uf /600V AC, from '84, or 8 United Chemi Con 25000uf 450/525
surge lytics? The oils are 2.5" dia (62mm can, 65mm bottom lip), no
mounting clamps. The 'litics are 3" dia, standard mounting clamps, all test
fine at rated voltages - didn't test the actual C of the 'litics (my meter
doesn't go that far, and too lazy to bother...
-dim

There it gleefully sat, 5 inches in height, shiny Al from around 1935,
and with +500v on the AL external surface.

I went to grab the chassis, then lift it across the bench, and grabbed the
electro like the nice handle it was.

AAAAHHHHHHOOOOOOUCHHHH!!!!

OUCH! I can feel that pain here myself.

The chassis somehow left a large dent in the ceiling, did a 360 on the way down,

and smashed a coupla tubes on de floor.
I somehow moved 10 feet faster than I thought possible, but at 20,
we were all indestructable, unlike the old radios we canobalised.

I've had it happen where I found myself kicked a second or
two into the future.

It was the start of a love-hate relationship with highish voltages.

I hope it don't convert to a fatal attraction.

You know your way around high voltage nowadays, but
be sure to exercise the usual caution.