Are Electrolytic capacitors stored for a year or more on the shelf useless?

[treez]

Is this true......a Senior Engineer told me this.
Apparently , if they don't get voltage on them regular, they just go bad and don't work?
Rather like rechargeable batteries.

 

[Audioguru]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

I have electrolytic capacitors stored for 50 years and they work fine. The first time they are powered they might have a little leakage current but it soon goes away.

There are "surplus" electronic parts stores in my city and they sell many old electrolytic capacitors. The only problem being the rubber seal on some of them has cracked and is stiff so the capacitor leaks its electrolyte.

 

[chuckey]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

Really old electrolytics have more then "little leakage" current when first used. It is a good idea to reform them by operating them with a current limiting resistor in series. Many capacitors used for audio coupling have a current limiting circuit driving them so they are OK. Power supply reservoir capacitors are most at risk, because there is very little current limiting, so If you switch on a really old Hi-Fi, it would be ideal if a current limiting resistor was included in series with the mains lead. I reckon, 5 hours at 60 % rating, should be good enough to put full mains on, but it might take a further 24 hours to get the leakage down to its minimum level.
Frank

 

[andre_luis]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

In fact, life cycle of Electrolytic Capacitors are quite smaller than others silicon devices, and it is represented by its MTBF parameters.
However, 1 year are too exagerated, otherwise no one equipment could expect 1 year of guarantee, due there are dozens of this component inside.

Anyway, I believe that 50 years as informed above could vary according to environmental temperature.
Here were I live, it is common the need to replace capacitos of equipments stored from many years.

( I believe that due to this component have some chemical components in pasty state, it could be affected by higher temperatures )


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[treez]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

thanks, do you imply, chuckey, that electrolytics are mainly mostly damaged by the inrush surge current into them at switch on?..After all, high though this surge is, it only lasts for a millisecond or so..surely its insignificant?

May I ask, are all capacitor types just as badly damaged by inrush?..eg Film, ceramic types?

 

[andre_luis]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

Polypropylene ones are most suitable to deal with higher inrush current.


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[chuckey]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

They do dissipate more power during the inrush and may suffer from an excessive Dv/Dt which can damage them. I was actually referring to a using an old electrolytic capacitor as a reservoir cap. In its actual state "as found" it may be more like 100 ohms with a 50 MFD capacitor across it so if its used on a 50V PSU, the leakage current will overheat the capacitor, after reforming the capacitor might be more like 500K with 500MFD across it.
Frank

 

[Audioguru]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

An old electrolytic capacitor might have a high leakage current that heats it too much for maybe up to one hour when it is first powered.
It is different from a normal brief inrush charging current.

 

[treez]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

wow...as low as 100Ohms.....just imagine that on the primary of an offline smps where that 100 ohms could be across ~300V.
So electrolytics, in a light bulb that's hardly used for a year, when that bulb is then next switched on, the lytics may well suffer horrendous heat for a while?

 

[dick_freebird]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

There is a seal, and its qualities (life) may be unknown or just
declared so by manufacturers who don't want to be on the hook
for storage life specs when they could push fresh product by
declining to guarantee old material already bought.

 

[betwixt]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

It would be interesting to know the real reason for 'de-forming' instead of speculating. Certainly in the past it was common practice to pre-charge old electrolytics through a resistor to limit the current if they had been in storage for a while, the process was called 're-forming'. I suspect the reason they deteriorate is something to do with them returning to their manufactured state before being polarized, in other words partially losing their polarization. In the old days of high voltage electrolytics, the trick was to add a 10K resistor in series with them, apply full rated voltage and monitor the voltage across the capacitor, it would sometimes take a minute or more to reach full charge, far longer than the RC time constant would predict. After discharging, it would work normally afterwards.

I know of one electrolytic manufacturer that has a room where they test capacitors before shipping, some of these will have been in storage until needed. They connect hundreds of them in parallel and power them up for several hours in a 'bomb shelter' room. After powering them down, an operator visually inspects and removes the exploded or bulging ones and the rest are shipped.

I too have capacitors 50+ years old, their ESR may not be perfect but it probably wasn't very good on day one compared to newer types. They still work perfectly well.

Brian.

 

[andre_luis]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

There was noticed many unfortunate products lots which presented failure due to bad quality manufactured capacitors after few years in operation ( became from no liable asian suppliers ). Perhaps there are some critical process on its fabrication just known by traditional companies, being probably the reason to be defined at some designs at the BOM precisely its brand.


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[Analog Ground]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

The original question was about a need to charge electrolytic capacitors periodically to keep them from going bad, like some batteries. For common, everyday parts, the answer to this question is certainly "No!". Inventory can sit in boxes for a year or more without being charged with no problems. If you are having problems with new parts within a few years you need to get a different supplier and manufacturer. Perhaps they are not new or there is a quality problem. BTW, this is all about aluminum electrolytic. Tantalum are different. That said, you do need to pay some attention to your inventory. Here is what Panasonic says about their aluminum electrolytic caps. The time period they spec is 10 years with a leakage current check after 4 years. I am sure similar guidance is available from other manufacturers.

"Leakage current will increase during extended storage. Capacitors should be stored in temperatures not to exceed +40°C and protected from direct exposure to sunlight. Under normal conditions, storage life can exceed 10 years.
It is recommended that the leakage current be checked for conformance to the specified limit if the capacitor has been stored for four years or more.
Storage may require reforming of the capacitor to reduce leakage current below the specified limit. This can be accomplished by applying rated voltage in series with a 1000 resistor for a time period of 30 ~ 60 minutes. The capacitor is acceptable for use if the capacitor leakage current is within the original specified limit or the capacitor is reformed to within the original specified limit. "

 

[Audioguru]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

I too have capacitors 50+ years old, their ESR may not be perfect but it probably wasn't very good on day one compared to newer types. They still work perfectly well. Brian.

I betcha they were not the cheap poor quality ones that are made "over there" and are sold on E-Bay today.

 

[betwixt]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

I think Marco Polo had not yet visited 'over there' when these were made. :smile:

Brian.

 

[m.mokhtar]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

I have very old electrolytic capacitors more than 15 years and I still using them without any problem at all

 

[andre_luis]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

I have very old electrolytic capacitors more than 15 years and I still using them without any problem at all

Statistically, those old capacitors are more susceptible do fail than newer ones.
Time storage, and time in operation decrease its life-cicle:
**broken link removed**

The equation that models reliability is defined bellow:
R(t) = e^ (t/MTBF)


Note there are many factors that impacts on its life-cycle, such as temperature and current regimen:
**broken link removed****broken link removed**


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[m.mokhtar]

Re: Electrolytic capacitors stored for a year or more on the shelf are useless?

If you are going to use these capacitors for timing you have to charge them using a series resistor to charge them near the rated voltage and the charging time must not be less than one minute, this allows steady state value of the capacitor to be reached.

my 15 years old capacitors I used more than 500 capacitors and for many years none of them failed.