Question about electrolytic capacitors

[gamer87]

How many days can I store unused electrolytic capacitors without electrical voltage but that this electrolytic capacitor does not present problems due to non-use and depolarization?

 

[berkeman]

Thousands. The main issue with electrolytic caps is that they dry out over time, so they have a limited lifetime. But we buy caps all the time that have been on the shelves for a couple of years. Also, operation at elevated temperatures speeds up their degradation.

Can you provide some context for your question?

 

[hutchphd]

More than you want to know is here. There is also a process called "reforming" the oxide layer which I have heard is important from a friend who is a tube head a good EE. From the article :

For antique radio equipment or for electrolytic capacitors built in the 1970s or earlier, "pre-conditioning" may be appropriate. For this purpose, the rated voltage is applied to the capacitor via a series resistance of approximately 1 kΩ for one hour. Applying a voltage via a safety resistor repairs the oxide layer by self-healing. Capacitors that fail leakage current requirements after preconditioning, may have experienced mechanical damage.[94]

I have no direct personal experience.

 

[gamer87]

I have electronic devices from 1990 to the present day that use electrolytic capacitors but I don't know the interval to use them every month, every year, every two years or more my intention is to preserve the electrolytic capacitors that they have defects by disuse

 

[hutchphd]

I think the Panasonic website used to have some information about this. Can't track it down right now.

 

[Tom.G]

From pg29 section 7.3.2 Storage conditions of:
https://www.tdk-electronics.tdk.com...2da2adf2b/pdf-generaltechnicalinformation.pdf

If not otherwise specified, our aluminum electrolytic capacitors can be stored voltage-free above stated conditions (from +5 °Cto+35°C, relative humidity ≤ 75%) for at least two years;

You might also be interested in section 10 Maintenance on pg 31.

(Take note that this is from one of the higher quality suppliers.)

Cheers,
Tom

 

[gamer87]

From pg29 section 7.3.2 Storage conditions of:
https://www.tdk-electronics.tdk.com...2da2adf2b/pdf-generaltechnicalinformation.pdf

If not otherwise specified, our aluminum electrolytic capacitors can be stored voltage-free above stated conditions (from +5 °Cto+35°C, relative humidity ≤ 75%) for at least two years;

You might also be interested in section 10 Maintenance on pg 31.

(Take note that this is from one of the higher quality suppliers.)

Cheers,
Tom

Does this rule apply to electrolytic capacitors mounted on electronic systems and with 30 years of life and use?

does this two-year rule not apply to any manufacturer's electrolytic capacitors?

 

[berkeman]

Does this rule apply to electrolytic capacitors mounted on electronic systems and with 30 years of life and use?

does this two-year rule not apply to any manufacturer's electrolytic capacitors?

I'm having trouble parsing your post.

Electrolytic capacitors degrade over time. They dry out and their capacitance value decreases. Does that part make sense?

Whether that causes a circuit to stop functioning depends on how sensitive that circuit is to the value of the capacitance. Does that part make sense?

Take a switching power supply circuit, for example. The output ripple will depend on the ESR and output capacitance values, and those will change over time and with temperature. When you write the datasheet for your power supply that you sell, you need to take all of that into account.

If you are just building a home-brew vanilla circuit board that needs some Vcc decoupling capacitance to maintain low-frequency signal integrity on the PCBA, then it may not matter too much.

 

[gamer87]

I referred to them unused stored and mounted on electronic devices with 30 years of age and use

 

[Tom.G]

Based just on past experience, 30 years is likely too old for most electrolytics. There is a large dependency on the initial quality of the seals, the purity of the Aluminium, and of the electrolyte. Twenty years, or less, is the most likely ballpark lifetime for decent quality devices.

I've had some that were not powered for a decade that were 45 years old and had leaked electrolyte through failed seals. In the same equipment, others showed no physical degradation. Some worked, some did not.

If there is no sign of leakage (no white stuff around seals), it is possible a few may still function. If they leaked, replace them.

For those without physical leakage, you can try reforming them. Over time the insulating layer on the electrodes dissolves back into the electrolyte, making them more like resistors than capacitors. This can cause them to overheat if they are in a circuit that can supply much current. If they are coupling capacitors between stages (not common) they can cause destruction of the tube in the following stage.

Reforming consists of applying a lower voltage for a period of time to start rebuilding the insulating layer. You then gradually increase the voltage to build a thicker insulating layer. This is not a 10 minute project, more like several days for really old capacitors.

If you want to do this with the capacitors still installed in the equipment you need a variable transformer to supply a lower line voltage, the most common brands here in the US are 'Variac' and 'Staco'. You start out setting it around 10% of line voltage and powering the equipment for a few days, then turn it up to 20% and let it run, etc., until you reach full line voltage or something fails.

Monitor the temperature of the electrolytics, if one gets warm go back to the lower voltage for a few days and try again. If one still gets warm, replace it.

Unfortunately, the above reforming is unlikely to be successful. It is a 'last resort' when trying to keep the original components.

Good Luck! and please keep us updated on your progress.

Cheers,
Tom

p.s. The other approach is to purchase new capacitors, cut open the old ones, and mount the new ones in the old cases. This keeps the 'look' rather antique but solves the problem of old, dead capacitors. If you take this approach, wear a dust mask because the dust from the dried-out caps is rather irritating, and you probably want to do it outdoors, not in the kitchen!

 

[gamer87]

I apply tension to the devices using them only

but I don't know the unused interval

 

[gamer87]

I have electronic devices from 1990 with electrolytic capacitors but I have no resistor and I have nothing to apply low voltage, what is the recommendation?

 

[DaveE]

Usually a really long time, (many, many years), but it depends greatly on the initial design, construction, storage and/or operating conditions. I don't think you'll get a useful generally applicable answer.

It's not on the radar for real electronic manufacturers because their inventory and QA systems won't allow collecting parts until they are ancient.

In service, some very large electrolytics (typically used in high current applications) should be replaced on a (pretty long) schedule, since they will dry out.

 

[gamer87]

i am confused my doubt

 

[berkeman]

I have electronic devices from 1990 with electrolytic capacitors but I have no resistor and I have nothing to apply low voltage, what is the recommendation?

i am confused my doubt

We are confused by your posts as well, but we will still try to do the best we can to help you.

Are you trying to restore old electronic devices to operation? Replacing old electrolytic capacitors is one of the main ways that this type of restoration is done. Are these old devices not working?

@dlgoff is our local expert in old electronic / electrical device restoration...

 

[DaveE]

i am confused my doubt

OK, but some things in life are confusing. Like the lifetime of electrolytic caps. I'm confused too. You may know more about this than all of the people out there that never wondered or aren't confused.

BTW, you can learn more about this by reading the web site of capacitor manufacturers. You'll learn more, but you'll probably still be confused.

Also, a related question: How do you know if an electrolytic cap is old or failing? You measure it's ESR (series resistance), and leakage current (parallel resistance); which isn't easy to do for most folks and may be impossible without removal from the circuit.

 

[gamer87]

My electronic devices are working correctly but I keep them stored and I ask if they are stored, will the electrolytic capacitors fail due to disuse? have been electronic devices since 1990 and have electrolytic capacitors I look for a time interval without using the devices but without the electrolytic capacitors failing due to disuse

 

[hutchphd]

I don't have any specific references but my general impression is that you are indeed correct in worrying most about the aging of the electrolytics. I think it would be prudent to power things up a couple of times a year after inspecting all the caps for signs of leakage. If there is leakage replace the component. Leave them powered for an hour or so.
The next most important aging issue is probably the condition of circuit boards, particularly for newer designs. Particularly look at the condition of the traces.
There are museums devoted to electronic devices. Surely someone at these places would give you advice. They would actually be knowledgeable!

 

[dlgoff]

We are confused by your posts as well, but we will still try to do the best we can to help you.

Are you trying to restore old electronic devices to operation? Replacing old electrolytic capacitors is one of the main ways that this type of restoration is done. Are these old devices not working?

@dlgoff is our local expert in old electronic / electrical device restoration...

When I'm doing a restore that has electrolytic capacitors, I replace all of them. The electrolyte does dry up as others have mentioned.

Good luck

 

[gamer87]

What happens to the chemistry of the electrolytic capacitor if it remains unused for more years? Are used electrolytic capacitors manufactured in 1990 totally different in the chemistry of off-the-shelf electrolytic capacitors?

 

[dlgoff]

What happens to the chemistry of the electrolytic capacitor if it remains unused for more years? Are used electrolytic capacitors manufactured in 1990 totally different in the chemistry of off-the-shelf electrolytic capacitors?

https://en.wikipedia.org/wiki/Capac...n_non-solid_aluminium_electrolytic_capacitors

Sound right @berkeman?

 

[berkeman]

What happens to the chemistry of the electrolytic capacitor if it remains unused for more years? Are used electrolytic capacitors manufactured in 1990 totally different in the chemistry of off-the-shelf electrolytic capacitors?

https://en.wikipedia.org/wiki/Capac...n_non-solid_aluminium_electrolytic_capacitors

Sound right @berkeman?

I'm no expert in electrolytic caps, but my impression is just that a part of it evaporates out of the caps over time. It's probably not cost effective to hermetically seal those caps, so the plastic layers that are used apparently are slightly permeable to the drying out process.

 

[hutchphd]

I believe the nature of the oxide layer and its insulating efficacy degrades with age and disuse. Then the resistance of the cap gets smaller and they start to run warmer leading to a bad spiral ending in disgorgement.

 

[dlgoff]

From Related Threads, this has a lot about the chemistry: https://www.physicsforums.com/threads/electrolytic-cells.60695/

 

[gamer87]

one person referred to using the electronic devices of 1990 every month for 1 hour, otherwise the electrolytic capacitors of this device will depolarize, dry and lose capacitance, is this true? I do not mean shelf electrolytic capacitors but electrolytic capacitors from electronic devices since 1990