Project REFORM: Capacitor Reforming Measurement and Demo Kit -> check your caps!

[f4eru]

Hello,

Capacitor reforming is a common, but often overlooked problem of electrolytic capacitors.
You just let an electrolytic cap sit unused, without voltage for some time, and the cap deteriorates chemically.
When using it again, it exhibits "some" leakage, the time to re-plate the oxide onto the foil surface, and all is good again.
This leakage often is overlooked in the normal device inrush current that nearly all SMPS show.

Problem is that this inrush can become very huge, and explode the cap, blow the fuse, etc etc ...
Often it is overlooked, because it's an uncommon problem of untypical users that store the gizmo for a long time.

Some uses are more prone to this problem, but basically all are affected, and cap manufacturers often don't put a guaranteed value in their datasheet.
Time to change this, and measure and publish a list of better caps that don't need so much reforming.

https://www.quadplus.com/post.aspx?PageID=224



I recently got a few hundred 400V electrolytic caps that are brand new but unused because it was found that they exhibit unusually high breakdown of the oxide, and need frequent reforming.
It could be a defective batch, or a bad chemistry choice altogether... The brand is an usual "questionable" manufacturer of caps.
These can show a reforming effect after only 1 month without voltage.

If enough people are interested here, I will develop and distribute a simple test tool for measuring the characteristics of the caps you use concerning reforming, and demonstrating the reforming effect to your manager or your students.

The idea :
- Small PCB regrouping the necessary hardware, to make the test setup fast to use
- Rectifier
- Current and voltage measurement with scope
- Simple slow controlled reforming with a high value series resistor from mains (useful also for reforming any equipment)
- Simple fast reforming with a very low value resistor (simulating a user just plugging the equipment to mains, with high current)
- Eventually a microcontroller with a coulomb counter and display for measurement
- Eventually a protected transparent housing
- Open source HW
- ....
- Of course, Included in the kit : 5 to 10 "bad" caps -> capable of demonstrating the reforming effect once per month each

Please vote, and make suggestions !

[WattsThat]

Apples and oranges. You’re taking a very specific situation (AC variable frequency drive bus capacitors) and attempting to cast a very broad net with it.

It’s borderline audiophool nonsense. You’ve got a bad bunch of caps. Bin them and move on.

[NiHaoMike]

I'm under the impression a scope is the wrong tool for that (scopes are primarily designed to capture very fast events while reforming is a very slow process), is there some little detail that can be detected with a scope like "micro breakdowns"? I'm thinking a very precise ADC connected to an Arduino would be a good way to track small changes in current.

I recently got a few hundred 400V electrolytic caps that are brand new but unused because it was found that they exhibit unusually high breakdown of the oxide, and need frequent reforming.
It could be a defective batch, or a bad chemistry choice altogether... The brand is an usual "questionable" manufacturer of caps.
These can show a reforming effect after only 1 month without voltage.

If they're small/cheap, send them to the recyclers and forget about them. If they're large (a few mF or more), sell them to amateurs looking to do pulsed power experiments, they won't care much about leakage and just want the most Joules for the buck.

[james_s]

I have never in my life re-formed a capacitor in anything modern. I think I have done it once in an antique radio but that was only a stopgap until I could obtain a proper replacement. If a capacitor is bad I just replace it.

[f4eru]

Apples and oranges. You’re taking a very specific situation (AC variable frequency drive bus capacitors) and attempting to cast a very broad net with it.

Nope.
All electrolytics are affected to some degree. Every SMPS is affected, most people don't see it because reforming happens invisibly in the form of higher inrush when plugging after a time unused.
industry VFDs are the only application where it is properly documented and handled, because they have 3 big factors making it worse :
- series connected caps, where reforming current makes an imbalance, and the upper cap can overvolt and damage the lower one.
- higher use voltage, 400V rectified with PFC gives about 650V
- common practice of keeping spares, and relying on them for critical stuff

I have never in my life re-formed a capacitor in anything modern.

Of course you have reformed many capacitors.
Just not in a controlled way. Everytime you plug in a SMPS that was unused for 3 months, the main 400V cap reforms.
It takes the form of a much higher inrush than normal.
Every cap has the effect. It cannot be avoided. And this is why every serious manufacturer of caps has it somewhere buried in their user guide to reform.

Try it out :
Choose a random modern SMPS lying unused for a long time. Choose one with no active gizmo connected as a load.
take a scope in single shot, monitor the current of your device in the 10s area, and measure the first inrush, let it plugged an your to fully reform, then unplugged an hour to discharge completely, then try again, you'll see a very much lower inrush.

[sandalcandal]

I think there was a similar thing that came out in the Silicon Chip magazine a while back albeit without the waveform measurement.
 http://archive.siliconchip.com.au/cms/A_112073/article.html
Edit working link https://www.siliconchip.com.au/Issue/2010/August/Electrolytic+Capacitor+Reformer+%2526+Tester

[james_s]

Of course you have reformed many capacitors.
Just not in a controlled way. Everytime you plug in a SMPS that was unused for 3 months, the main 400V cap reforms.
It takes the form of a much higher inrush than normal.
Every cap has the effect. It cannot be avoided. And this is why every serious manufacturer of caps has it somewhere buried in their user guide to reform.

Try it out :
Choose a random modern SMPS lying unused for a long time. Choose one with no active gizmo connected as a load.
take a scope in single shot, monitor the current of your device in the 10s area, and measure the first inrush, let it plugged an your to fully reform, then unplugged an hour to discharge completely, then try again, you'll see a very much lower inrush.

Obviously when I say I have never re-formed a capacitor I meant I have never taken any specific steps to do so, I just operated the equipment normally.

Ok, I could do that, but for what purpose? Maybe the inrush is higher the first time I plug it in, so what? Why do I care? I plug in equipment all the time that has sat unplugged for months, I don't care if the inrush is higher, the equipment is designed so that it can be plugged in after sitting in storage without blowing up.

[station240]

Have you look at the LV capacitor tester Mr Carlson('s lab) made ?

https://www.patreon.com/posts/another-released-17569473
have to donate to his Patreon to get the circuit to build it though, so not true open source.

[f4eru]

interesting approach, thanks
It doesn't reform, just measures the leakage with high sensitivity.

My device would be more a characterization device to help quantify thee effect of "unaware" reforming (straight plugging in), so help design the device, help in evaluating capas perf, check QA of caps, especially when production changes brand

[Siwastaja]

IMHO this is something actual designers of whatever device should take care of.

Either by making sure the caps never blow up (or blow the fuse, or exceed rated inrush, or cause any other damage); this is the strategy chosen by all consumer, industrial, medical low-power SMPS manufacturers and it seems to work very well. (I haven't taken any steps to actively control capacitor reforming of any SMPS I plug in, ever, either.)

Or, if this is impossible or carries too much of a risk for a product like VFD which uses banks of series caps of large size, then take the necessary actions during design of that device. For example, use better balancers for the series caps (than nothing, or very large value resistors). Or, add reforming step, like normal precharge (inrush limiting) but with a larger value resistor and a relay which bypasses it. "Reforming capacitors, 2 minutes remaining, please wait..." Yes, this will increase cost but aren't these expensive products anyway? By taking care of reforming internally, they could brag about it in marketing as they would have a more reliable product.

If a product blows up if special trickery (often poorly documented, or completely undocumented!) is not followed, then I think it's a badly designed product.

[JohnG]

If you could demonstrate an increase in capacitor lifetime due to managing this reforming process, then there might be more general interest. Lifetime of electrolytic caps can preclude their use in a number of applications, but there are often some serious penalties paid to avoid them.

John