Reforming capacitor in old or vintage equipment

[zoltm]

Saw someone posting a thread on how to charge a capacitor, it reminds me of asking for collective intelligence in reforming capacitor.

Any best practice and what are the tools required? What are the capacitors that have good chance of being reformed while some may not have any hope and does not worth trying at all?

Thoughts? 

[Simon]

what do you mean by reform ? I think on the whole they have to be replaced. Electrolytics have a finite life.

[T4P]

Reforming? Might as well replace them
No point being a idiot like the vacuum tube audiophoolery community and reforming caps

[SeanB]

If you want to keep the look the best is to remove the old capacitor, gently open it ( or not so gently in some cases) and remove the dead foil and paper insides. Then clean it, dry it and put a modern replacement inside the old case, close it up after connecting the new leads to the old case parts. place back in the equipment and enjoy.

If not then cut them out at the terminals and solder in the new ones to the leads, without disturbing the existing wiring and terminals too much.

Reforming will work for some, but is at best a short term stop gap, as often they will go short circuit if placed back in use.

[nukie]

Reforming capacitors is discussed in many manufacturers datasheet. Nichicon has good info, read it.

tapatalk

[notsob]

Silicon Chip Magazine Aug 2010 issue # 263 is a capacitor reform project

http://www.siliconchip.com.au/cms/A_112073/article.html

there should be some useful info for you there

[vk6zgo]

Try QRZ.com.
They have a "Boat Anchor" forum,& many folks have had good results with reforming Electrolytic caps,others suggest replacement.as several people have on this thread.
Back in the day,re-forming was more often done on "New Old Stock" capacitors,which were correct mechanical,& electrical replacements,but may have been 20 years old at the time.
It was unusual  to re-form caps already in equipment,because the old stuff had probably not have been out of service that long.

[SeanB]

I did once get a job lot of CTS10 capacitors that had been in storage for 40 odd years. I reformed 100 and tested them, and compared them to 100 that were out of package. No difference, so my incoming QC was reduced to quick test only.

[Chris Wilson]

I have always wondered if equipment using tanatalum or aluminium foil with gel dialectrics electrolytics show longer capacitor life with less issues if used regulary, or left unused? For example, I have a new old stock Tektronix 7633 scope. I found one bypass elecrtrolytic just showing signs of weeping and changed it. Had this scope not been unused from new until a few months ago, but had been used say weekly from it manufactire in about 1989, would the caps likely be better or worse?

[Rerouter]

if you want to try reforming an older electrolytic capacitor, one that hasnt obviously leaked, you set up a low voltage supply of a 1-5mA, this will breakdown most of the internal shorting, and by cycling it between drained and charged, it will slowly repair, after say 20 cycles, test it with a multimeter, you will get funny readings as it slowly charges off the measuring current, but if is a consistanly low reading, say under 200 ohm, when stabalised, it means you need a few more cycles, and might want to try higher currents, depending on the size, say 0.2A, this should make any more serious internal shorting self heal,

if all of that doesnt help, it has probably leaked, and had hard mineral deposits solidify between electrodes,

[MartinX]

I have reformed a couple of electrolytic capacitors in the past, I just connected them to a power supply through a series resistance that limited the current to a couple of mA put one multimeter in series to measure the current and another one measuring the voltage over the capacitor. When you turn the power on the voltage will slowly climb sometimes showing an erratic behaviour, the current will be fluctuating to, then you just wait and see if the leakage current stabilizes at a low enough level to be considered good, if it does then the capacitor may be usable. Older high quality capacitors were sometimes designed with reserve electrolytic in them, if you shook them you could hear the fluid sloshing about in there, and apparently it could last for 40 years.

[David Aurora]

Reforming? Might as well replace them
No point being a idiot like the vacuum tube audiophoolery community and reforming caps

And here we are again with you getting a bee in your bonnet about tubes...

Yep, I can imagine tube enthusiasts being prime candidates for people who need to reform caps, and here's why- a lot of tube gear is getting old, and whether it's old tube or old solid state it's increasingly hard to find suitable part substitutions. Tried to buy any big ass, odd value axial caps lately? Yeah, that's what I thought haha. When you're going through an old piece of gear trying to get it up and running enough to give it a quick test, if there's hope of reforming a cap it's going to be FAR quicker than the wait to order new ones (assuming you can actually find them).

That's not to say I wouldn't try my best to swap them out, but I'm not going to go and spend $100 or whatever on hard to find caps with crazy shipping times just to get the thing to turn on for a quick test.

[nukie]

I have never looked closely into axial caps design. Can someone tell me what is the problem with replacing axial with radial caps? Let's just say the long leads on the radial caps can be bent so it fits the mounting points. Radial caps are usually smaller, lower esr and higher current handling. Of course some audiophile will argue that radial caps don't sound that good and the long leads of the stretch radial caps will pickup emf noise.

tapatalk

[SeanB]

No difference internally in the actual capacitor. The difference is the leads are coming out on opposite sides on an axial unit, and one lead is a flat foil strip spot welded to the case during final assembly just before the inner is placed in the tube and sealed. Generally modern units are smaller as the foil purity is better and the foil is much thinner, the separator paper is thinner and better quality and the electrolyte is formulated to a tighter purity. The etching is done so as to make a larger surface, as the etching is nearly through the foil. All make it smaller, so in most cases the radial will fit in the place of the axial, you just need to extend one lead with a short wire and fasten it down so that vibration does not fatigue the one lead off.

[T4P]

Reforming? Might as well replace them
No point being a idiot like the vacuum tube audiophoolery community and reforming caps

And here we are again with you getting a bee in your bonnet about tubes...

Yep, I can imagine tube enthusiasts being prime candidates for people who need to reform caps, and here's why- a lot of tube gear is getting old, and whether it's old tube or old solid state it's increasingly hard to find suitable part substitutions. Tried to buy any big ass, odd value axial caps lately? Yeah, that's what I thought haha. When you're going through an old piece of gear trying to get it up and running enough to give it a quick test, if there's hope of reforming a cap it's going to be FAR quicker than the wait to order new ones (assuming you can actually find them).

That's not to say I wouldn't try my best to swap them out, but I'm not going to go and spend $100 or whatever on hard to find caps with crazy shipping times just to get the thing to turn on for a quick test.

Unless the cap was designed to be ESR limited, there's really no point in not having to scramble to find a modern electrolytic to replace.

[David Aurora]

I have never looked closely into axial caps design. Can someone tell me what is the problem with replacing axial with radial caps? Let's just say the long leads on the radial caps can be bent so it fits the mounting points. Radial caps are usually smaller, lower esr and higher current handling. Of course some audiophile will argue that radial caps don't sound that good and the long leads of the stretch radial caps will pickup emf noise.

tapatalk

The bit in bold is the key issue. I doubt any sane person gives a crap about which way leads come out of a cap, but for practical reasons it's much easier to replace axials with axials most of the time. If you can bang an easy to find radial in there instead, great. But sometimes you can't without extending leads, heat shrinking it all together and whatnot. Pain in the ass.

[saturation]

Better.  High quality electrolytics typically are only "rated" for 5-10,000 hrs, yet if powered on continuously lifespan of even cheapos is substantially prolonged, to the point there is no real set date limit. 

In many metrology labs equipment are kept on 24/7, and if that rating were true, 1 year is about 8800 hours, most high end gear would blow electrolytics by the 2nd year; they actually last for decades. 

There is a formal way to reform electrolytics if kept is storage for years:

http://www.everyspec.com/MIL-HDBK/MIL-HDBK-1000-1299/MIL-HDBK-1131B_28461/

The many methods are similar: slowly ramp up the voltage until it reaches the rated voltage, while current limiting the input to prevent caps from blowing if they are leaking heavily and could overheat; with reforming the leakage current should drop, if not the cap is lost.

There is no formal procedure I know of for incircuit 'reforming' of gear that have linear supplies.  For vacuum tube devices, tubes should be removed.  Dont' use the variac method on SMPS.

You'll need a variac and an AC ammeter.  Find or estimate quiescent current; usually this can be inferred from the manual based on its normal operating power consumption, like if it were as a bench DMM.

Ramp the input voltage from 60V to 120V over 1 hour, watch the current draw of the device.   Raise the input voltage 10V/10min.

Keep the current draw, <= quiescent current for each voltage step. 

If the current rises over quiescent there maybe a leakly cap that needs more reforming time.  Wait another 10 min, or longer, until the current drops.

Once the cap reforms leakage current drops, so that's good feedback that's the culprit, and you can clearly ramp up the voltage to the next level.

If you cannot ramp the input voltage without a rapid current rise, then either the caps are gone or their is a short somewhere. 

Once the gear is working, leave it on for a day, then in the future at least turn in on for 1 hour monthly, to insure the caps stay healthy.  There is no way for me to verify this is the right length of time,  it could be shorter, but as is, its worked empirically for years.

There are other methods and other consideration for the DUT, that may not take kindly to low input voltage.  But this 'slow startup' process is a way to insure your eBay gear, that may not have been used in years, has a better chance at working without modding than being torn down for service.

I have always wondered if equipment using tanatalum or aluminium foil with gel dialectrics electrolytics show longer capacitor life with less issues if used regulary, or left unused? For example, I have a new old stock Tektronix 7633 scope. I found one bypass elecrtrolytic just showing signs of weeping and changed it. Had this scope not been unused from new until a few months ago, but had been used say weekly from it manufactire in about 1989, would the caps likely be better or worse?

[bingo600]

If you have a SCPI compliant PSU , like the HP 6632B or E36xx's.
You could have a look here.
http://www.brouhaha.com/~eric/software/wrec/

/Bingo

[vuhq]

hi
I was wondering if you guys know any company in the world that can reform big pile(say around 70K) of electro caps(680uF).Any suggestions and guidance would be much appreciated.

Thanks
Donnie

[edavid]

hi
I was wondering if you guys know any company in the world that can reform big pile(say around 70K) of electro caps(680uF).Any suggestions and guidance would be much appreciated.

Thanks
Donnie

Why do you think they need to be reformed?  Have you tested them?

[vuhq]

No I have not tested them but I have bought this stack(70K) one year back and I was told by United Chemicon that the shelf life of these components is 3 years. I am planing to use these components over the next seven years period.Hence my assumption is I will need to reform these parts in two years at the latest.Thanks for your attention and response.

[edavid]

No I have not tested them but I have bought this stack(70K) one year back and I was told by United Chemicon that the shelf life of these components is 3 years. I am planing to use these components over the next seven years period.Hence my assumption is I will need to reform these parts in two years at the latest.Thanks for your attention and response.

I don't know why they quoted the 3 year shelf life, but they will have definitely not need to be reformed after only 10 years.  It's probably a solderability issue.  You should ask the vendor.

[vuhq]

Could you explain why I would need to reform them after only ten years.Is there any white paper or any other reference document you could point me to?