This is also an issue with grossly overrated capacitors: If you use for example a 50V capacitor on a 5V power rail, it will initially work as intended, but with the operating voltage being so low the capacitor can't properly reform the oxide layer and will lose its formation over time. It's always a good idea to leave some safety margin for the eventual stray voltage spike, but too high is bad as well.

In the Telecom Industry, we are running into this more frequently, as legacy equipment shows its age. Most of our older Voice Switches employee electrolytic capacitors, to add further filtering to our primary office battery of -48 to -53 volt DC. Over time, these filters caps develope leakage currents outside acceptable limits, & thus they are fused accordingly, to reduce catastrophic failures. As part of our testing, we precharge caps with a series light bulb, of a known value. When the light extinguishes, the cap is charged with minimal leakage. However, if the bulb remains illuminated, it's time to replace the cap. It's old-school, but is time tested, & relatively simple to do.

This man found a way to turn hardened criminal capacitors into reformed members of the board, WITH ONE SIMPLE TRICK!

I like how you reversed the footage of you taking a capacitor apart to show how it went together. That was smart!

The best part of this video for me is that now I understand the reason electrical equipment disconnected for a long time will bust when reconnected again. Thank you!!!

I build and repair guitar amps, mostly tube amps with supply voltages that can many times reach over 500vdc. A very common practice is to use an incandescent light bulb in series with the power cord as a current limiter when powering up an amp for the first time. The light bulb will light up, then dim with current draw... a nice visual reference, like the needle on your analog multimeter. I was taught to bring the voltage up incrementally to "break in" or "form" the new caps... Now I know exactly what's happening!

Having a background in electronics. This video is very very helpful. You did a heck of job. Well done sir.

Shelby, you have risen to a new level!!! I'm SO impressed by the technical information, backed by your research and experience here. And most valuable of all, you explain the science behind all of this...so I thank you for making this very professional-quality video and publishing it here for folks like me to learn from...thank you so much!!! Fantastic!!!

That web interface is pretty friggin slick!

I really don’t understand any of this . But I loved this video. You are so well spoken, genuine , and easy to listen to. You are a amazing teacher and a great salesman. Keep up the good work. Your awesome man.

It might be worth mentioning that for non-polar paper capacitors, reforming like this doesn't work, instead the paper dielectric has absorbed moisture and you need to get it out, for example putting the capacitor in molten beeswax above the boiling point of water... or putting it in an oil, and then pulling a vacuum on the capacitor that will boil off the water as well. I've done this and it works

This is the most comprehensive video about capacitor reforming I've seen. Thank you.

For something like the Data general, you can definitely appreciate why reforming would be required. Also great explanation, thank you for sharing!

An easier and more elegant method is to use a Adjustable Current Limit Supply. Dial in your max current, set the open circuit voltage about 15% to 20% below the rating of the Cap. After stabilization keep the current limit unchanged but raise the open circuit voltage to the rating of the electrolytic. BTW, you did a nice job describing the idiosyncrasies and reforming of Electrolytic's! It's been over 65 years since first studying them. Wakodahatchee Chris

2 things to note here: 1) the sinkrate of the current is also greatly depending on the capacity because it is high on discharged capacitors. When they charge, the current goes down. 2) why didn't you use the current limiting function of your psu? It nearly does the same but without bumps. You can even charge lithium ion batteries with such psus, just set maximum voltage and current. It's called CCCV. (Constant current, constant voltage) or IU.

One of the best and comprehensive presentations I've seen.

i worked at a power supply manufacturer for about 30 years as a technician and then engineer. Our units supplied anything from 3v at thousands of amps to hundreds of volts at several amps. The older designes used computer grade caps with screw terminals and these became hard to source. I used to setup a group of caps with individual resistors in series with each cap. I'd start at about 25% of the rated voltage and check the srop across each resistor. After they settled forwn I'd increase the voltage to about half the rated voltage and do the same thing. Then I'd go up to 75% and let things settle for an hour or two. before going home for the day I'd go up to the full rated voltage overnight. After each voltage level I'd check the drop across each resistor and anything over 5-10 MA leakage was a failure (these were old can caps). Atfer the last full voltage run I'd put a red dot on the caps that passed. This proved to be a good indicator of cap longevity but anything over 10-15years was very iffy, even if the caps were NOS. Old caps just are not as well sealed as new ones so they can dry out just sitting in a box. cCps in use can last a very long time because they are kept active, I've got tesxt equipment that is 60 years old with 500v electrolytucs that still work just fine because they see use (Heath 0-400v regulated power supply I built in HS).

One thing I would like to see covered and examined is how many manufacturers cut corners and install capacitors in devices that are barely able to handle the rated voltage in their installations. A couple cases in point here that I ran into years ago... I had purchased a plasma TV when they were all the rage. It worked fine for about a year and then I noticed longer and longer start-up times for it. Then one day I hear the dreaded high-pitched "pop" from inside and smell the all too familiar odor of the electrolyte. I set the TV aside and we bought a new LCD one. Everyone seems to understand the power demands of the plasma versus the LCD (and now LED) sets. However, I was not going to give up on the plasma. I had heard of them failing all across the country it seemed!! I was convinced of a simple explanation. Taking apart the plasma TV took longer with the about 800 screws (exaggerated of course) holding the case halves together, I found that it was neatly laid out with separate boards for the various functions, one of them being the power supply. As an aside, these power supplies have NOT radically changed and are still used in all sets! Looking at the board I clearly saw the popped open capacitors and others that were bulging. I looked at the rated voltage of them and quickly decided that the manufacturer had not allowed any leeway as they were right on the actual voltage applied to them. I took down all the ratings and then went to e-Bay and bought a whole new set of them at DOUBLE the rated voltage. Now, here's the most interesting part... The circuit board was actually set up to use larger capacitors than what were installed!!! This was plain to see by the pictorials drawn right on the board and the extra space around the originals. Nothing else on the board had extra space. The new capacitors arrived, and wouldn't you know they fit the actual available space perfectly. That plasma set worked fine afterward, and it is still working like a champ in my living room 20 YEARS later!!! I only wish I had started repairing plasma sets for other people as so many were thrown away for nothing more than $12 in caps and a little labor on my part. My second great instance was the control board for my $1 Jacuzzi hot tub that failed (yes, it cost me $1 for an eight-person hot tub!!). It sort of mirrored the plasma TV in how it gradually failed. I took the board out and saw it looked almost perfect. A couple caps were peaked though but not ruptured. I found the test sequence on a web search and proceeded to measure everything until I could go no further. At that point I sent an e-mail to a person in AZ who could rebuild the boards. I gave him my thorough test results and he was so impressed that he called me! He said that it was going to be an easy fix since I knew my way around and that I wasn't going to believe what I had to replace. The capacitors were my first guess and was right. Again, I ordered double the existing voltage rating and oddly, there was extra space on the board again... Seeing the manufacturing pattern here? After replacement the hot tub was back in operation, and I was relaxing in it until we moved out of that house and sold it before that move. For $3K in case you're wondering! So, the question remains as to why manufacturers are shortchanging the capacitors in everything. Are they simply doing it knowing that they will fail and the average person will run out and buy a replacement device? I smell a rat here....

I've got years of analog electronic experience and never knew this was a thing. I'm still learning, cool!

The self-healing page at 4:49 is about metallised film capacitors. Entirely different from electrolytics.

Ha I've got that same radio shack multimeter I've had since I was a kid in the 80's! Learned more about capacitors here than in all my years replacing them. Great work!

Offtopic: At the end of the video the dot matrix printer... I haven't seen one in over 20 years now.. I miss the sound of it. LOL! I want one...again.. Ontopic: great video! That's why some old stuff just don't work any more after setting them away for 20+ years...

That was quite an eye opener! Made me realise something about these old hard drive supplies... some of them take 3 spin ups to get going, amazing it works at all it won't die.

Used to repair welders and my boss showed me this neat thing where we put a run-out gauge on the side of a capacitor and tested the welder with our load bank. Watching the caps change diameters under use was interesting. It had no diagnostic value as far as i know but it was interesting in a " huh? Well would you look at that" kind of way.

The idea of reforming old capacitors is cool and maintians the original look of the device. I would rather scrap them when you are working on expensive or antique ( vacuum tube ) equipment. But I love how you go into the detail on how to do it.

OMG with this talent, you should be explaining policies to pass bills in the parliament

I did hear about this about 55 years ago. Now I understand it. Well done!

For a minute there until you spoke, I was thinking Garth would pop in from behind the camera and I was being transported into another Wayne's World video on Public Access Television.

Well done! We run into this at CHRS all the time. Reformed many; some are just too far gone. Thanks for spreading the knowledge!

Just came across this - thanks Mr. @TechTangents ! Some used audio gear I have acquired is in an unknown state, so I'll be doing the variac and light bulb trick because all of them are most likely old enough to have old-school, linear power supplies, not the modern, switching power supplies ("switchers"). Of course, I'll crack them open just to make sure. It is good that you mention that switchers cannot have their voltages slowly ramped up without possible bad outcomes. I have also one piece of my own, pro audio gear that is about 25 years old but was powered on only once for a few minutes to make sure it worked - and then shelved and never used again. It will be very interesting to see what state its caps are in. Wow = @Mr. Carlson himself commented somewhere below - he da E-Man !

Fantastic info. Love the idea of using GPIB to automate. I have that same bench meter and a PSU with GPIB. I’ll be giving this a try in the future.

Really great video - great explanation. Seems consistent with my experience with it. Nice to have the video to share with others. Many thanks. Subscribed. Cheers

You sir, are a perfect, ideal, clear and concise tech speaker/writer! I am impressed and educated. Bravo # 1 !!!! Perfect speaking voice as well. Bravo #2 !!!

I deal with AC variable speed motor drives and occasionally have to reform the capacitors in them. Manufacturer recommends to do it every 2 years if they've been powered off. They are usually 450V capacitors in a series/parallel setup. I use an 120V AC variac, a 600V:120V transformer in reverse and connect to the AC input of the system. The drives have a pre-charge diode and resistor for normal starts and a thyristor bridge on the 3ph power in. I can bring the voltage from 0 to 600Vac (0 to about 850Vdc) using a standard 120V wall power. I have also done a similar manual setup with a 600V rectifier and a rather large resistor (I think it was 10ohm, like 100W) to make my own DC supply for models that did not have a rectifier circuit.

It was really fun watching you work on this stuff live!

Another factor in speed of leakage current slowdown at 15:09 might be different capacitance values as the circuit is basically a high pass filter loaded by resistance of the analog meter. Oh and if you want to automate without multimeter you could consider a source measure unit, they have more current ranges and some can go up to 1000V (but yeah expensive sadly). Nice vid thanks.

Hey, thanks for a nice and in-depth explanation! I've known about reforming capacitors ever since I started restoring tube gear, and I sometimes do that both in existing devices and new devices I build using antique components (can electrolytics etc.). Generally I test them before reform attempt. If there's no capacitance, it means that the lead has corroded internally and the capacitor is dead. Otherwise I'll attempt reforming, bringing the cap up on a 300VDC power supply through a current-limiting resistor, by setting the voltage to get ca. 5mA out of it, leave it for a few hours and bring it up again after the current drops below 0.5...1mA, observing the max rated voltage. Looks like I could use a CC/CV high voltage supply for that and for tube circuit prototyping :)

Reminds me of when I ran the process a few years ago, with decent results. Saved a bunch of money on some very large caps, with an 80% success rate. Ultimately other problems with that PSU led to retiring it and installing a modern switchmode option, but it was good practice.

Incredibly helpful. Someone suggested that I reform some new power supply filter capacitors before I install them (they had been sitting more than two years) and I had no idea what he was talking about. After watching your video, I completely understood what I was doing and why I was doing it; was able to set up the circuit, and do the job safely and correctly for all four 33K ohm capacitors. Excellent and entertaining presentation, very clear and understandable. Thank you!

Thanks for covering everything from the basics - I suspect people from the "bad caps" days will imagine that "reforming" just means the same (euphemistic) "remanufacturing" or "refurbishing" and all the baggage that comes with that era.

I'm just starting out to learn about electronics/circuitry and most channels are hard to understand and keep up with but this is oddly very easy for me to understand. I would love to see more videos like this about basic components or ics, or different logic systems etc explained for noobs like me

Very interesting. Thanks for the informative post. I would love to hear what Mr. Carlson would say to this video.

Really all you need is to rig up an incandescent light bulb socket to the power in. The light bulb will feedback any over wattage and protect anything you are working on

An intelligent video about reforming, not just DO or DON'T because that is how I do it. Thanks Shelby.

Great video topic, and well explained. I first encountered the concept of electrolytic capacitor reforming in a manual for an industrial variable frequency drive (for speed control of AC motors, if you're not familiar). It was a totally foreign idea to me, and I was surprised to learn that it's necessary due to the way electrolytic capacitors work, as you described in the video. I had no idea at the time, and I still think it's pretty wild.

I'm so glad you made this video. I've also done a bunch of research on this but you've put it all together very nicely and made ti relevant for people who like restoring vintage computers. Well done - thanks!!!

Well researched videos about topics that no one else bothers with is exactly why I'm here. I love this video, and good information to have as an Auto Tech in an ever expanding electronical field.

This show puts you on my A list. I like how you use the use the junk i bought when i was a kid. God bless Radio Shack and the battery club. And remember Boys and Girls a new cap can have issues that will make you cry. Good luck to you all on reforming your cap world. Take it from me when you do this stuff wear the safety gear. Best Regards Jack.

Very interesting, good knowledge to have. Filled in some gaps of things I didn't understand. Thanks

This is the definitive video on capacitor reformation. Thank you TT!

15:46 - Those might be oil-filled caps,in which case..I don't believe reforming is needed,or even possible,since they aren't electrolytic. Side note: Old oil-filled caps were often filled with PCB (Polychlorinated Biphenyl).. If they are leaky,dispose of them properly! That stuff is nasty and hazardous.

As an electrical engineer BSMEE I have heard of capacitor reconditioning and reforming. I have worked on and designed Amplifiers and power supplies ( Linear and scan rectified)and Frequency generators and Programmable control hardware for 40 years. In the field it is easier and cheaper just to replace a suspect capacitor. On vintage equipment is another story. If the capacitor is not easily replaceable because its in accessible or because modern capacitors are much smaller for the same value uF or even for ascetics, Then reforming may be an option. Problem with reforming is you do not know the quality the final result and reading the uf capacitance value is no indication. It may last a day or a year. But a new Capacitor is always better than reforming an old one. You post no credentials. But you provided a in depth wel explained explanation of what is happening on the inside of a capacitor. Suggest you do a video on the capacitance of components that are not capacitors, like a Zener diode, a MOV, a step up transformer, A Transistor, An DIP IC socket, a touchscreen and why this is so.

Great content and delivery, had to like and sub. Cheers from Calgary.

Cool video, with the perfect amount of detail. Thank you.

Great explanation of the reforming process! I generally use my small HP bench supplies (6212A or 6216A) for caps rated up to 100V, or a 6515A for anything higher. All of them operate in either constant voltage (what people generally think of when working with a power supply) or constant current mode. For the 621Xs, short the output and turn up the voltage a bit, then adjust the current limit for somewhere between 5 and 20 mA. For the 6515A, this step isn’t necessary as its output is fixed at about 5 mA. Once the current limit is set, remove the short and set the power supply to the cap's rated voltage. Turn the power supply off and connect the cap, then turn the supply on and it’ll increase the output voltage to maintain the current setting until it reaches the rated voltage, at which point it will change to CV mode as the leakage current decreases. Less babysitting needed that way, and if the cap doesn’t fairly quickly get up to the rated voltage, you know it’s toast. I monitor voltage and current like you do - voltmeter across the cap, and milliammeter in the low side between cap and power supply negative terminal. I came upon a box of big caps I had squirreled away a few weeks back and have been reforming like a madman lately. Most have come back nicely; only a few went into the garbage. In my opinion, at least for larger caps, it’s definitely worth a shot before just blindly replacing them. Certainly those used in older high end test gear (HP, Tek, Fluke etc.) are normally very high quality components that will last a long time if properly cared for.

This is the video I was looking for, thanks buddy and KZfaq suggestions

With small capacitors, probably not worth the hassle. The big beefy ones though, definitely worth trying if you got the equipment for it. Those guys are NOT cheap, and are often difficult to source!

So many people missing the point here. There are certain caps that you either can't buy anymore or that can be prohibitively expensive. If you can reform them, you can potentially save a device from becoming ewaste.

Thank you very kindly for everything you do, Mr. Shelby Technology Tangents.

This is a super interesting discussion, and a great explanation (or part of one) why the 12v ac adapter I bought 10 years ago stopped delivering 12V 2A and became a questionable 11V 250mA supply. If you have a project that calls for lots of coulombs and you have the e-waste, I say go for it. I can envision a few scenarios for it but honestly I would probably just go with new caps for anything serious. I'm not an expert, I don't have all day, and capacitors are cheap. 👍

You’re a good teacher! Thanks 🙏

Thanks, I didn't know that you could repair caps like this until your video.

A clear and concise explanation. Keep them coming.

Thank you for Recycling these!

Great video bro! Very well explained.

Very instructive 🤔 I have a suggestion to automate this with a regulated power supply: set your lab power supply to current limitation mode and set the voltage to the target voltage. The regulation will gradually up the voltage with respect to the current limit. To be tested before reforming the caps of your vo stage Marshall 😏

Great video very informative ! Caps are magical things. I'm always looking for caps when opening a device. When you see some Elnas or Nichicons or Mundorfs or Black Gates or Philips BCs in a high end device they are simply gorgeous.

Excellent video! I like that ammeter method.

Very good explanation and description of the process and chemical situation (coming from a 35 year EE analog design engineer) but the prices of just replacing the capacitors with newer ones makes it hard to justify the time spent. Mr Carlson ( on Utube) is a master of replacing especially very old capacitors including mostly non-electrolytic capacitors. I think your video is actually very educational and between the lines, give more reasons to replace than reform (especially the unknow ESR factor you mention in the video. The newer switching power supplies actually rely on low ESR type capacitors to limit the internal temperature of modern capacitors.

That was fascinating, thanks for showing us.

This is wealth of information. Thanks!

Heared that for very big commercial ones, so the example that I remember was a capacitor that was big as a coffee cup and used for a ~220V AC-motor inverter, but for the smaler standard electrolyte capacitors i always got told that they 'dry out' and in the same company where i saw the big one that has to be reformed after some weeks of not using it, they changed ALL Elkos as a standard procedure when refurbishing electronic modules.

I'm sure you probably thought of this or someone else mentioned it. It's very cheap and easy to make a HVPS using a AC transformer from an old tube amplifier, etc that you've rectified with a few diodes and a cap or two to lessen the ripple. Of course, the end result won't be an automated process like you have now but, you'd at least be able to reform caps rated 500+ volts when needed. Yes, this either requires a Variac to adjust the AC or if you're inclined, you can create a simple circuit to adjust the DC side instead eliminating the need for a Variac. Since I don't reform caps very often (hardly ever), I just use the Variac to adjust the AC voltage to intern adjust the DC voltage. There's many videos on here of "reformers" people came up with. The majority of people who will want to reform some caps don't need an expensive setup like you have. Buying a lower voltage transformer and making a voltage doubler/tripler circuit will save you some money even further but, used transformers aren't expensive and can often be had for free. I just use one I took off of an old Hammond organ amplifier that's 600 volts. Honestly though, I only like to reform "Can" type caps with multiple capacitances and rare ones you can't really buy anymore. Otherwise, I just buy new ones that are generally much smaller and have better temperature ratings.

Really interesting. I knew what a capacitor is and that they sometimes fail but that was about it. I now know a bit more and what to look out for on a failed capacitor. Interesting to learn about reforming and when to try it v replace. Many thanks for taking the time to make this and share your knowledge.

Interesting plus the Compaq hat is cool and the dot-matrix printer snapped me back a substantial number of years. Thumbs up for educational.

Nice one! Just what a sceptic like me needed :) A few times you made it sound like a cap is supposed to “have a load” or “be a load” which is a bit confusing, but in this context it does make a little bit of sense, considering we’re talking about ESR. I still have a hard time finding a use case since it’ll still be easier to replace an old one and less risky - time is money and a new one is less likely to blow up 3 months later leaving the neighborhood soaked in electrolytic. Sometimes the original caps might be a big part of the aesthetic though - in that case reforming is your only bet. Always good to have another tool in your arsenal, thanks!

Wow, great video, thank you!

Great video on reforming caps.

Perfect timing. I have a SWTPC 6800 which has a minibar Coke can-sized electrolytic that needs reforming.

If you have a reasonable digital CC-CV bench power supply with 1mA current resolution (like a Rigol or a Miniware) you can do moderate-voltage caps without all the fuss - just set the power supply's voltage limit to the capacitor's rated voltage, the current limit to a few mA, turn it on, and let it sit. If after a few hours the power supply is still in current limited mode (hasn't hit the target voltage yet) then your cap's leakage current is higher than the limit you set, and you will have to use good judgment to decide whether to bump up the current a bit more, or discard the cap as faulty.

I was just thinking why not write a program to automate this and bam....there's python. I love your channel dude!

I studied Electrical engineering and even I didn't knew about reforming capacitors. Though to my excuse, I was mostly into writing software, designing digital circuity and radio/em stuff. VERY NICE!

OMG I can't wait to see the inside of capacitors!!!!

Very well made video. Easy to understand and follow. I would have hoped that you got your hands on a professional RLC meter to actually do a before/after comparison of a reformed capacitor. You don't have to buy one for thousands of dollars, there are places that rent out equipment like that. We even have companies that send us test equipment for free in a "try before you buy" kind of deal, so we can play with the instruments for a few weeks and then decide if we want to buy it, or just give it back with no cost or strings attached.

An interesting and will presented video, learnt a lot from it. I love your feature creep into a web gui. 🤓

I doubt I'll ever be needing to do it, but now I know. Thanks!

2:40 - apart from the issues of reforming a cap, this small snippet demonstates why older caps have very high inductive reactance Newer designs offset the foils so the ends can be folded over and the contact lead touches ALL the coiled up foil on its side of the insulator @kpanic: it's a tradeoff of voltage spikes. I spent a lot of time in the 1980s stripping out and replacing failed 16V caps on 12V rails (plastic cases, they usually _split_) with 50V ones. These were in landmobile base station receivers worth about $1k a pop so it was worthwhile. We ended up replacing ALL caps on sight if we found older devices in them as there were too many instance of replacing the failed ones only, to have other caps fail in-service several months/years later (with a 50-200 mile roundtrip to replace the things including a slog up a mounatin goat track)

One of my fav youtube channels man. Keep it up. Also wish i could grow hair and copy that flow.

Wow…..(head scratching begins?) That was insightful.

Thank you! This video gave me a true nerdgasm! Haven’t had one of those in a good while! 14:10

09:45 Ha,ha. I have one of those multimeters (I have a blue one) I got it from Tandy in 1984 and I still use it.

Nice info, thank you for sharing it :)

Great video and explanations!

Great video. I didn’t realize that you could do this with capacitors.

I learned something new today! 👍

I am a Armature Radio operator and I have a lot of old amps and radios. I have always used a variac to bring the amp back on line.

This is why I only use Brawndo electrolytic capacitors. They have a visible fill line to make sure they never run out of what capacitors crave.

This was fantastic. New subscriber now. :)

I know this is late to the game. I want to offer a tip. Drain your bench power supply feed before you connect it to your capacitors. A lot of the power supplies don't shut off the current on the output side of their capacitor, but instead shut off the current driving their capacitor. This is how I ran 20 volts into a 3.3 volt part because even with the benchtop power supply completely turned off, it still held 20 volts on its capacitor. So always check your bench power supply before connecting it to low voltage parts.

I've seen shango066 reform capacitors in old TVs many times with a variac and light bulb, so I had a vague idea of how it works. Never expected to find a tutorial.