I has some of these and even though they are new and never used, I was wondering if they are safe to use or do they dry up as well? Thanks!

How old?
Go the the mfg web site and look up the shelf life.
They may might need to be re-formed.

It looks like there is a lot of information on re-forming capacitors. I have quite a few of them, I'm glad I don't have to show them away. Thank you for your help!

If they are 10 years old reforming results are not very good and if they do reform it doesn't seem to last. Don't burn up your capacitor tester trying to reform them, make a dedicated power supply to reform them. They can be restuffed.

DM

The electrolytic cap seems to be the indispensible Achille's heel of all electronics. Yea they do deteriorate whether used or not. Maybe varies depending on storage conditions. I don't know if taking them off the shelf every few years and reforming them would enhance shelf life or not. And then there are variables like who made them and such. Better types have longer life. You may have failures in cheap ones pretty quickly and have radios with 50 year old caps that apparently test and function OK. But the largest use of them nowadays is the surface mount types for low voltages and compact stuff. So you can still buy discrete wire lead ones. And even newly made ones in cans. But the prices for those is pretty steep as compared to the past. I myself would be wary of very old cans that have been setting around for decades. As for restuffing. IN many cases it is a great deal of work and not worth the bother where the modern replacements will fit under the chassis out of sight. But you got free labor to do it. Just the time may be precious.

Actually, my concern is with my radios and equipment. I probably have a couple hundred of these NOS capacitors, but it is not worth it to me to chance hurting my antique radios or equipment, so I will have to toss them. Not a big deal. Thanks, for the information!

Nobody can tell you what you have without looking at it and testing it. While it is true that some consumer replacement grade "can" electrolytics are hopelessly dried out and useless by now (except for re-stuffing), there are lots of military and high quality commercial "cans" that are still going strong after 65-75 years, better than anything you can buy new today for conventional power supplies and similar circuits. What it all boils down to is what the OEM was willing to spend with their suppliers when the caps were produced. A company making household TV sets might have paid $0.50 for each can electrolytic while a company like HP or Tektronix might have paid $5.00 for each of theirs. The difference is in the quality of the seals, the purity of the aluminum and electrolyte, and the care with which the cpacitors were formed, assembled and tested--things you cannot determine just by looking at them.

If you have not applied any voltage to them already, the correct thing to do is set up a small bench supply with a voltmeter and a milliammeter. The capacitor is connected in series with a resistor and then two are connected across the power supply. The resistor is essential to protect the milliammeter in case a capacitor shorts out. Assuming you use a 10-mA meter. the resistance should be calculated from Ohm's Law so no more than 10 mA of current will flow into a short circuit at the full working voltage of the cap.

The capacitor is then gradually brought up on the power supply, keeping the current under 10-mA, until you reach 50% of the working voltage of the cap. Stop there and wait. The current should continue decreasing and stabilize at some low value. This may take half an hour or more with some caps. What you are looking for is a final reading under 2-mA. Assuming this is achieved, the next thing to do is rapidly turn the power supply voltage up to the full WV of the cap. If it is good, the current will rise again but it will soon fall back down under 2-mA. But if the current goes up and stays up for a long time, or never goes below 2-mA, the cap is dried out and should not be used for a long-term repair or construction project. Those 10-mA/2-mA numbers come from old Army literature. If you are testing smaller axial or radial lead electrolytics which are less able to dissipate heat, the leakage current should not be allowed to exceed 2-mA at any voltage.

The purpose of the test is to determine how much electrolyte remains inside the capacitor. Caps that have already been brought up on voltage cannot be tested by the above method because they will have already started to reform and you won't get an accurate idea of how much electolyte remains. After they have had voltage applied for at least half an hour, all caps should always be tested for leakage current at rated WV, power factor (or dissipation factor or ESR), and capacitance. Leakage for can capacitors should be under 2-mA, power factor or dissipation factor should be under 10%, and capacitance should be at least marked value or higher. In multi-section electrolytics, it is important to check from leakage from one section to the other(s). Since this tests two capacitor sections back-to-back you should see about the same leakage that you'd see for one section. But if the leakage is very much higher, the rubber insulator between the terminals may have failed. The cap may still be usable if the two sections are to be connected in parallel, otherwise it's no good.

It might also be mentioned that if a cap will always be operated on a voltage under its rated working voltage, for example a 250 volt cap in an AC/DC radio where the cap will never see more than 140 volts under any circumstances, then it is usually considered acceptable to test it at the voltage it will actually see in service. However, I would have my doubts about any new or NOS capacitor that does not test well all three ways at its rated voltage, after it has had a chance to fully reform.

If that's too much trouble to go to, or they test bad, I hope you'll consider selling them in the classified section here or on one of the online auction sites. Re-stuffed or as display duds they still have value for chassis restorations where the original cans were removed.

This post has proven to be some very interesting information for myself. One other problem that I see is that these "Can" capacitors are multi-valued. my guess it if one value turned out to be good the other or others should be as well, but I doubt that I would be comfortable unless I tested them all. I have a box full of NOS "Sprague" cans. I have listed as : Twist-lok, TVL-3648, 140-140-29 MF, 350-350-350 WVDC.

I took a picture of one of them, but of course they are all of different values.

I have boxes full of N.O.S can type capacitors from various manufacturers.
There are no general rules, some respond favorably to a (slow) reforming process, others don't and remain leaky.
I wouldn't use them in any applications where long term reliability is an important factor.

MFGR date 1969, week 26.

Assuming it passed leakage test, I'd use it, underrated, maybe 250-275v max. There's one of approx same age and voltage rating in my homebrew transmitter that runs 24/7, it's B+ is maybe 175v max.

I never give a second thought of caps from mid '70s & newer, mostly pop 'em & go. When reforming, if current doesn't drop rapidly in 15-20 second voltage increases, it probably ain't no good...

Honestly, It's just not worth taking a chance hurting my radios or electronics. I enjoy rebuilding my equipment knowing I am using good quality parts and there is just too much risk using these. I want to thank you all for your input and time.

I would be concerned in equipment that is not fuse protected. You can add fuses to stuff anyway for that added peace of mind. Even if hardwired in under the chassis with leaded fuses. Dried out caps are more likely to cause a hum or ripple issue anyway. The ones that I have seen short out and blow are either hooked up wrong or overstressed somehow. Not that they cannot short, but what I have seen is loss of capacitance. With raised ESR.

i my opinion, ...The most economically sensible approach to the consideration of using old-style old technology electrolytic caps is ... just toss them away!

The extremely low price and high quality of the new smaller e-caps versus the headaches and potential failures and wasted time to re-troubleshoot and RE-repair...makes the use of the old ones almost TOTALLY senseless.

Pbptx, I totally agree with you.

If you have a bunch and they are NOS, somebody will buy them. Look at sold auctions on eBay.

I save these and restuff them with new ecaps if the original can capacitor is missing from my radio. That helps keep the original appearance of the top of the chassis.

Yes, electrically they are a bit risky, but don't toss them.

They can even be used to fill a chassis hole, where the original is missing and the replacements are mounted under the chassis.

Ted

Well, you're right about low price, anyway.

Quality? Not really. New caps are much smaller and designed to operate at much higher temperatures than they were in the past. But most are optimized for high frequency (read switching or digital applications). They tend not to have the high ripple current capabilities of older capacitors at 50/60 Hz or 100/120 Hz. And while ESRs of some modern caps are vanishingly low today, that is not necessarily a good thing when you are trying to protect vintage power transformers and rectifier tubes from high repetitive current peaks that will shorten their lives. Like anything else, quality varies all over the lot. You can get some really fine new electrolytic capacitors that will go the distance, or you can get some really shoddy ones that will only last a couple of years if you are lucky. The problem is, you don't always know which is which just by brand name or seller. Counterfeits exist and even the major distributors sometimes have trouble telling them apart from legit components.

Potential failures? New capacitors sometimes fail too.

Troubleshoot and re-repair? Same as above; new capacitors sometimes fail too.

It all depends on what you want to do. Capacitors made today are built for today's applications and for today's circuitry. Capacitors built dozens of years ago were made for the applications and circuitry that existed back then. If you are just trying to repair something and not really worried about meeting specs for performance, then whatever works, works. Set the bar low enough and you can call anything a win as long as it doesn't go up in smoke. But if you are trying to fix something so it meets the same specs as it did new, that's a different story. Then you need parts that match the originals in every detail, and it is possible that you cannot even buy new capacitors that match the originals in every way. But if the original parts are still good, nothing is easier than just leaving them there and re-using them.

I also refuse to go along with the "it's old so it might fail" line of reasoning. If a part has suffered some kind of degradation or defect that might cause it to fail in the not-too-distant future, your testing ought to show you that. Otherwise it is the testing that is inadequate, not the parts. I have elaborated at length in other posts how to do that, such as the "excess electrolyte test" mentioned above. That is intended to tell you if a capacitor still has lots of time left, or if it is nearing the end of its useful life. Testing for leakage, loss (power factor, ESR, or dissipation), capacity, and leakage between sections is a lot of work, but not as much work as re-stuffing a can that was still good, or living with a product that never works quite as well as it did before.

If the point has not been made:

Multi-section canned electrolytics can and DO fail from leakage from one section to another, not often but has happened and can baffle a technician...

I have been "sitting" on some 50 or so NOS Sprague canned electrolytic, long past their sell-by date. They are odd values, a few are the "Self-Ranging" types for example 100 to 150mf 100 to 350 volts. I will be moving them along soon...

Hayseed Hamfest should explore developing a "Universal" empty can. If a customers are reluctant to buy their custom product, the can at least would be a saleable product.

FWIK an empty can requires special tooling to make a complete and effective closure...

Chas

I would love to see somebody make a "refillable" replacement electrolytic can. One that can be taken apart and has space and terminals for three or four radial lead caps of the user's choosing, and has terminals on the bottom so it fits and looks like an original.