Shelf life of Electrolytic Capacitors

[sam coniglio]

Okay,


My lab is stocked with many electrolytic capacitors that were purchased new up to 20 years ago from Mouser Electronics.

Should I toss these in the dumpster. Some of these are quite expensive and in some cases difficult to replace in todays market.

We use these for equipment that uses linear power supplies. Also we use them for lab experiments in R&D and/or hobby projects.

What about Tantalums, ceramics ect.


Another problem is tough to determoine.

How long does the classic EPROMS that we are typically used in legacy electronics?

Some equipment that is multiple decades old are still being used in industry.

Why?

Because they are not tied in with PC operating systems. The firmware in such devices is straightforward and I/O if needed is based RS-232 communication protocols.
Before you turn up your nose at the idea of using older equipment; please consider simple applications that are mainly implemented via hardware. They are user friendly and reliable.

Okay, to summarize:  We should not use stale capacitors, but what constitutes STALE.

Cant we use an oscilloscope to check for excessive ripple. Who cares what the ESR is or its capacitance value.

So invest in a good scope and save your money that you would have spent on an expensive ESR meter?

yes? .... No?

Take care guys long live the Intel 8035C Microcomputer CHIP.

Sam Coniglio

Dave keep up the good work!    I love your show!

 

UV erasable EPROMs are not advisable for use in repair of older equipment.

 
 

[iampoor]

I would imagine your environment (humid, dry, hot, cold etc) would play a large part...

Interested to hear what the pros think. 

[calexanian]

No worries. As long as they are decent manufacturers. We have a large supply of caps we bought in volume in the 80's and have not used since in production. We use them around the shop and in personal projects and have never had any problems. I would not use them in anything I was selling, but for projects go right ahead and use them. As for the tantalums I think you will be fine as well. They are actually amazingly stable if not abused.

[SeanB]

So long as the seals are still intact ad not discoloured or showing a white deposit around the leads or rivets for those with snap in connection, and you take a sample and reform it to rated voltage via a 1k resistor, then check after an hour that it is still lower leakage than the spec, and afterwards check the capacitance and ESR ( after discharging it) is still within the specified limits then they will be fine.

I tested a thousand units, and after the first 50 just did a sample test on each pack, as all had passed after being in a store for 30 odd years. I just reformed them all at rated voltage and after a while ( 500) I did not even bother either.

[Seekonk]

Last year I had a 40 year old electrolytic with screw terminals I put in a supply. A fault applied double the voltage for a half hour, it was almost too hot to touch.  It was a remote location and didn't have a spare.  Let it cool down and it has been running fine ever since.

[SeanB]

Old electrolytics often were very conservatively rated for voltage. They typically ( I remember for these ones I used) had a 75V rating at 25C, and a 50v rating at 125C, with a typical device often surviving having 75V applied while operating at 125C ambient inside the case. The large can units often were formed at nearly double the rated voltage, so that degradation during storage would still leave them able to operate at rated voltage. modern units are run at the limit, the voltage rating is the formation voltage, and exceeding it will kill it very fast. Your one got hot because it was busy reforming oxide to survive the increased voltage, and the current flow doing this heated it up. You definitely shortened the life of the unit, but as it likely is being run very conservatively the halving of operational life still will mean it will do a decade or two in service.

 I have a Sangamo capacitor in a can by me, still unused. Type 500X, 500X203U006AB2B, 20 000 uF 6VDC Made in USA in week 34 of 1975. Wonder if I should pop it on a LCR meter and see if it still is within spec.

[Evil Lurker]

Older electrolytics seems to be manufactured to much higher quality standards vs. the new stuff coming out of China these days. Then again they might all be the of the basic same quality and construction of previous generations but their lifespans are greatly reduced due to increased ripple and heat tolerances listed on the datasheet. In other words, it is like taking the engine block out of a soccer mom's grocery getter and then using it in a high performance race car and expecting it to hold up for the same number of miles. But, I'm no capacitor manufacturer.

Yes, these caps absolutely can be salvaged as long as the electrolyte has not leaked out or evaporated. It is good practice, at least in my opinion, to "reform" any old capacitor prior to putting it into service. Reason being is that the oxide layer on the rolls of aluminum foil used inside the capacitor can chemically change over time and colloquially speaking in the case of capacitors that have been in service they even "get used to" whatever particular voltage the capacitor was typically operated at. Reforming is simply a process of slowly charging a capacitor in small fractional voltage steps to the capacitors maximum rated voltage over a period of 12-36 hours using a variable low noise power supply and a current limiting resistor before each cap in case there is much leakage current until the cap's oxide layer reforms. In theory if this is not done it may or may not have much of any immediate effects but if not done there may be some irreversible chemical detrimental changes to the oxide layer and/or evaporation of the electrolyte from the cap heating up.  At least that is my general understanding, but again I'm no capacitor manufacturer.

[rsjsouza]

As others have said, old capacitors have larger tolerances than newer ones, but I would definitely test them before putting on a project - also, as calexanian mentioned I would not put them on a system for a customer.

I have a bunch of capacitors from the 80's and 90's that are still very well within spec (mostly Siemens and Philips). However, a few drifted off spec and one detail to look for is a smell of fish inside the box - an indicative the fittings on some of them were letting the electrolyte to escape.

Therefore a test I did was to put capacitors in individual bags for a couple of days and see if the smell was still there. I then found that several "in-spec" capacitors had this smell as well, which was indicative of a short lifespan.

Just like others, I have some old capacitors still going strong: two chassis-mounted Teslas from the 60's (100+100uF/400V and 50+50uF/400V) and one chassis-mounted Siemens from September 1980 (75000uF/25V).

 

[Dr. Frank]

Electrolytic "wet" capacitors (Aluminium Electrolytic Capacitors) can survive decades without noteworthy losses in capacitance or increase in ESR, but only when powered on regularily.
Examples are many old HP or Fluke equipment, up to 40 years old.

If stocked only, the Al2O3 dielectric layer will degrade by the wet electrolytic inside.
The capacitors then won't withstand the rated voltage any more, and will draw a big, maybe destructive current when being powered with full voltage, after years of storage.

For that reason, after about 7 years, spare part capacitors (these wet electrolytic ones) will be scrapped in our electronic manufacturing plants.

You may "reform" this dielectric by carefully charging the capacitor with a current limited voltage in first instance, say a few milliamps constant current,  compliance voltage should be set to nominal voltage. Then the decrease of the residual current should be monitored. It will reach after some prolonged time, the specified current leakage current of several µA, again.



Frank

[Kjelt]

Time for a DIY automatic capacitor reformator 

[Seekonk]

Can I have all your out of date capacitors?

Three phase inverter manufacturers have procedures for using inverters stored a long time.  Basically powering up for two days before using.

[Dr. Frank]

Time for a DIY automatic capacitor reformator 

 In Germany,we already had Martin Luther, I think.

Therefore, a Dutch should build such  an apparatus, but nailing the schematics on a church door, first. 

[German_EE]

Every electrolytic capacitor I put in a project gets two tests:

1) I measure the value. The tolerance on these devices is very wide (-20% to + 80%) and I want to make sure that it's close to the value on the outside.

2) A quick ESR test.

So far I have found two or three capacitors that never made it to the soldering stage and I do A LOT of constructing. Just buy or build an ESR meter and you will be fine.

[Kjelt]

In Germany,we already had Martin Luther, I think.
Therefore, a Dutch should build such  an apparatus, but nailing the schematics on a church door, first. 

Probably since the dutch invented the capacitor than known as "Leidsche fles" (bottle from the city of Leiden) in 1744 by Pieter van Musschenbroek.
But then the Germans claimed to be the first in 1745 by Ewald Georg von Kleist, figures most Germans are louder than most dutch   

I have not many out of date capacitors unfortunately fortunately, so building an apparatus for that purpose would stall my other projects for which I also have too little time 
Might be a nice new product for Dave.

[dexters_lab]

Another problem is tough to determoine.

How long does the classic EPROMS that we are typically used in legacy electronics?

UV erasable EPROMs are not advisable for use in repair of older equipment.

generally decades, EPROMS do slowly loose their memory due to background radiation slowly reducing the charge in each cell. They can be refreshed, just read -> erase -> write back the original data

i think i am right in saying the quicker an eprom erases under UV would be an indication of the remaining charge in the cells?

[Alex Eisenhut]

In Germany,we already had Martin Luther, I think.
Therefore, a Dutch should build such  an apparatus, but nailing the schematics on a church door, first. 

Probably since the dutch invented the capacitor than known as "Leidsche fles" (bottle from the city of Leiden) in 1744 by Pieter van Musschenbroek.
But then the Germans claimed to be the first in 1745 by Ewald Georg von Kleist, figures most Germans are louder than most dutch   

I have not many out of date capacitors unfortunately fortunately, so building an apparatus for that purpose would stall my other projects for which I also have too little time 
Might be a nice new product for Dave.

Guys, guys... You *both* have great countries I want to live in!

[Kjelt]

Hey it was just good fun 
We (dutch and german) tend to tease eachother now and then.

[SeanB]

Correct, but you can ignore the erase cycle and simply read, write back and compare. As the cells always decay to a "1" ( for Eprom) just writing the "0" bits back is sufficient.

There have been Eprom erasers which powered the UUT and used a ripple counter ( glitches are not a worry here) to run through the address space for the unit, and simply using a 8 input AND gate to see when the outputs were all "1". This is used to reset a timer, so when there have been no resets for long enough the lamp is turned off as the device is now blank.

The Dutch have cheese, the Germans bread and decent beer. You can mix them well.

[CatalinaWOW]

I also have had good luck with old electrolytic capacitors, some now 60 and 70 years old.  Whether to use old stock in production equipment would depend on how old the stock is, what you advertise as the life of your product, local laws on the content of "new" equipment, the consequences of a field failure and whether the cost of a reforming step in production was excessive.  It might make sense in some cases.

Old EPROMS lose programming for several reasons, including background radiation.  Some of the reasons are temperature dependent.  Most were specified to have a very low probability of a bit error over ten years at max rated operating temperature.  These ratings usually had a pretty fair theoretical margin in them (As Yogi Berra said "Predictions are hard, especially about the future").

The conservative rating combined with the fact that most EEPROMS don't spend much if any time at max temps they are quite likely to survive well beyond ten year specification.  Reprogramming should restore them greatly, although all of the other semiconductor aging mechanisms would still apply.

[Alex Eisenhut]

If we're talking old caps, just wanna mention that high voltage caps are sometimes rated with a minimum voltage, below which the capacitance really goes down.

So don't rely on low-voltage capacitance test as a measure of goodness for these caps. Just check for shorts and toss into circuit.

[Conrad Hoffman]

Some caps survive storage for a long time and some don't. IMO, the best test is to reform them with a supply and a big resistor for an hour, then measure the leakage current. If the leakage current meets spec, odds are high that value and dissipation factor will be OK and the cap will last a good while longer. Probably not as long as if it were new.

[SeanB]

Took that 20mF capacitor and measured it with the LCR meter. Overrange..... so used the $20 component tester and it came back, 32.82mF, 0.07R ESR and loss factor of 4.3%. Now busy reforming on a power supply at 6V3, via a 820R resistor ( nearest to hand) and I will check it again after a few hours. Takes a long time for the RC circuit to charge up, it was at 4V4 after a minute.......

[Dr. Frank]

Hey it was just good fun 
We (dutch and german) tend to tease eachother now and then.

Corrrrect!
I really like the Dutch!!!

Played basketball with several, when studying in Aken, often traveled to Netherlands, Maastricht (patatas frites), Emmen, groene haring met zwevelen ( ) in Katwijk, dear engineering colleagues in Eindhoven, but frontier was closed every time, Netherlands and Germany played football against each other..

But next week, it's Koningsdag, I' m very excited. Hopefully, it's fine weather!!!

Frank

Btw.: Dry electrolytic caps don't suffer from degradation..like tantalums.
Ceramic caps also do not degrade..
Only problem, for each electronic component, is the oxidation of soldering pads

Frank

[SeanB]

They found all those bicycles, in a sealed store in a warehouse in Frankfurt a few years ago. The German government will give them back, provided the Dutch claimant can produce a receipt with the frame serial number on it, and can identify it in a parade with some similar bikes.........

BTW, I have Dutch in laws, and my father studied in Germany pre war.

[dexters_lab]

Correct, but you can ignore the erase cycle and simply read, write back and compare. As the cells always decay to a "1" ( for Eprom) just writing the "0" bits back is sufficient.

good point