How to Recondition (Reform) Electrolytic Capacitors and Why

[Topcat]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

^
I know this is probably cheating (or those that have this kind of gear are just spoiled), but using the leakage test function with the button hold-down rod on a Sencore LCR, this will reform caps in an awesome manner. I believe the LC53 was the first Sencore LCR that would do this, I have a LC102.

[redwire]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Bipolar electrolytic construction I thought is the usual two-foil but with symmetrical etching? Ref. 3.1.8 https://epci.eu/capacitors-electrolytic-capacitors/
They behave like two back to back series-connected electrolytics but have a problem if the capacitance or leakage current is not matched between the two sections.
If there is imbalance, one capacitor can see reverse or over voltage which leads to its demise.
So I'm skeptical you can reform one side without damaging the other.

It's an old Mallory NP4510, must be a motor starting cap.

[eccerr0r]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Finally some actual critical thinking! Indeed I was thinking that the standard reformation process would 'damage' the other layer...because of this, I almost think that there's really no advantage to reforming these.

I'm not sure about what the expected leakage of these devices should be however. The one I have seems to be leaking quite a bit in both directions - not sure if I can get it up to 400+V without it blowing up due to leakage.

I'm surprised motor start caps would be electrolytic, thought most were oil-paper to deal with the rapid and frequent polarity changes, though now I'm not even sure what the use of bipolar electrolytic caps are...

[pc7fan]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Finally some actual critical thinking! Indeed I was thinking that the standard reformation process would 'damage' the other layer...because of this, I almost think that there's really no advantage to reforming these.

I'm not sure about what the expected leakage of these devices should be however. The one I have seems to be leaking quite a bit in both directions - not sure if I can get it up to 400+V without it blowing up due to leakage.

I'm surprised motor start caps would be electrolytic, thought most were oil-paper to deal with the rapid and frequent polarity changes, though now I'm not even sure what the use of bipolar electrolytic caps are...

Usually, bipolar electrolytics are intended to be used intermittently, unlike film/oil caps. this is mainly due to them usually having higher ESR. Remember that they're simply back-to-back electrolytics, with either the anode or cathode internally merged, like Redwire's post shows.

They use large canned bipolar electrolytics in induction motor starters because of the following:
* they're cheaper than film/oil for the same capacity, at the cost of higher ESR (hence heat, then they pop if ran too long), but;
* start capacitors are usually connected ONLY when the motor is spooling up (i.e. not at operating RPM), so if everything like the centrifugal switch is working properly, the motor will not use the starter cap when running properly. Refrigerator, freezer, air conditioner compressors are a common example use of this. Some of them may use a starter winding with a similar setup instead of a starter cap.
* smaller induction motors like in regular ceiling fans and desk fans will not have a starter disconnect, they will usually be using a film cap for its start/run capacitor. Those can be run continuously.

[mhp]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

hello every one
why some aluminum electrolytic capacitors are green and some are black?

[Per Hansson]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Finally some actual critical thinking! Indeed I was thinking that the standard reformation process would 'damage' the other layer...because of this, I almost think that there's really no advantage to reforming these.

You could reform it from an AC source then, just use a resistor to limit the current.
This is the way I reform caps anyway: no need to limit the voltage (as long as you don't exceed the voltage rating of the resistor).

[renato87]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Ceramic type smd capacitors, polyester mounted on a PCB electronic circuit and stored for long periods of time without being energized without use, suffer from the same problem as aluminum electrolytic capacitors, losing capacitance, high leakage current...?

[momaka]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

^ No.
These don't have any electrolyte that would break down, so they don't care how long they sit stored... well, to a point. Some PE/film caps may develop micro-cracks in their cases, leading to moisture ingression and short-circuit. A good example of that are old RIFA safety X2 caps on the line input. But apart from those, ceramic and film caps are probably the last thing that will fail due to sitting in storage too long. And even electrolytic caps aren't that fragile. I plugged in an old CRT monitor last year that had sat in storage for 10+ years (could be close to 15, actually.) Was a bit "lethargic" to give a proper focused picture for a minute or so... but eventually woke up and works fine. It was a Sony Trinitron 15" CRT with cheaper quality caps (Jamicon 85C stuff) inside. I find the Japanese 85C caps do a lot better - hardly any deterioration in storage, even after 15-20 years.

[bigbeark]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

momaka

I just revisited this thread and wanted to ask about the diode used on your breadboard on your original post. What is it's purpose, and if needed what value should it be? It's not mentioned in the text.

[momaka]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

Oh sorry, figured it might be easy to figure out, but maybe not so.

It's just a regular diode used for simple reverse polarity protection. The red wire you see on the left is where I will normally have the positive (+) lead from my power adapter, and the yellow wire is where I connect the negative (-) lead of my power adapter. So the diode is wired with the Cathode side connected to the (+) bus, and the Anode side to the (-) bus on the breadboard. That way, if I mistakenly connect my power adapter in backwards (+ to - and - to +), the diode will simply short-out my power adapter but not allow more than -0.7V to appear on the output.

So far, I haven't made this mistake yet (not on the breadboard anyways)... but it's good to have it just in case. I think I put it there very early on when I got that breadboard. The diode I used was an FR153, if I remember correctly (just something I had in my junk spare parts bin at the time.) But really, any 1-2 Amp, 50V+ diode will do here... unless you use a power supply that has a lot of power. Connecting such PSU in reverse could blow the diode in pieces and open-circuit it, then send the full reverse voltage to whatever else is downstream. But for power adapters under roughly 40 Watts, such small diode will usually work OK for protection.

Just to explicitly mention, of course, this diode is *not* necessary. But always good to have.

[slybunda]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

not possible to directly hook up cap to battery without resistor?

[lti]

Re: How to Recondition (Reform) Electrolytic Capacitors and Why

No, you need some kind of current limit. Otherwise, it would be the same thing as just powering on the equipment after all those decades in storage.

[socketa]

Is it better to store electrolytic capacitors in a charged state?

I reformed some 2200uf 6.3V 2008 new old stock MBZ

I raise the voltage in such a way that the current doesn't go much higher than 1mA, wait for it to drop to 0.000A and then raise the voltage again until around 1mA is drawn, and then falls to 0.0000A, and repeat... until 6.2V is reached

And observed that if they are left connected to the bench supply turned on, for about 12 hours
that their charge drops more than others that have being reformed for two days (12hrs X 2)
and if they are reformed for three days, even better (how much better, i didn't take note of though)

I reformed 3 caps for 12hrs, then reformed the original 3 caps pus 3 more for 12hrs, and then those 6 caps plus three more for 12 hrs),
which created three groups of caps that were reformed for 12, 24, and 36 hours
Subsequently, from memory, the value of the voltage that is retained after about 12 hrs is about 1V less - about 5V or so
and the difference between the voltage that is retained by the caps, in each of the three groups, is about 100mv - probably less as the caps are charged for longer periods

So with this in mind, it seems that electrolytic capacitors benefit from having a charge applied to their dielectric
Which suggests that it's better to store the capacitors in a charged state;

which is contrary to what AI states:

"AI states that:
Storing charged capacitors, especially those with high voltage ratings, can lead to several issues, including potential damage to the capacitor's dielectric (oxide layer)"

[momaka]

I don't see how storing a capacitor charged can damage its dielectric and I've done it as a test on quite a number of caps I have reformed too. What's interesting is I didn't find much difference between the caps that were stored fully charged (after reforming) vs. the ones that were not stored with charge. Only the ones that weren't reformed and stored without a charge seemed to go bad quicker - in my case, I was (re)using Rubycon MFZ 6.3V 2700 uF caps pulled from scrap Xbox 360 motherboards. As I have found over the years, all of these are unstable and bound to go bad, much like UCC KZG 6.3V caps did. So for these, the only thing that mattered is that the reformed caps (both ones stored with a charge and without) lasted a bit longer than the ones that weren't reformed. But again, these particular caps are known to have issues. With other caps that aren't known to have issues (e.g. UCC KMG, Nichicon VZ, and etc.) I rarely have problems with reforming them, even after many (10+) years of sitting without seeing a charge.

That said, all of this is just my own conclusion from my own experiments. In any case, I would NOT trust a SINGLE word out of any "AI" search out there. If the AI can't point to a reason why, then it's making shit up (or rather, taking garbage from who knows what "source".)

[stj]

even if you perform magic on the chemistry you cant fix a rotting or hardened rubber bung or corroding aluminium can - keep that in mind.

[VioletGiraffe]

all of these are unstable and bound to go bad

In what way do they go bad, is it just a loss of capacity, or is there something else to check for?

[stj]

if the chemistry breaks down they create gases and slowly blow the can apart or push the liquid out of the bung around the wires.

[socketa]

What's interesting is I didn't find much difference between the caps that were stored fully charged (after reforming) vs. the ones that were not stored with charge.

Over what time period was that?
It would be interesting to see a comparison over a year
The three capacitors that i left reforming for about a day for longer than another three, (and then charging them all up to 6.2V together), have retained 4.4V, and the other three have retained 4.0V after about four days of being disconnected from the power supply
(both sets of caps had no observable DC leakage current greater than 0.0000V at 6.2V - as i was thinking that leaving them refoming for a longer than suggested period, at max voltage, might not be good for them)
so it appears they have benefited more from this particular extra long time reforming at their rated voltage
probably verging on needless perfectionism here; as what has being mentioned prior is totally adequate, in terms of being practical.
in the words sung by grace jones, "i'm not perfect, but i'm perfect for you"

[momaka]

In what way do they go bad, is it just a loss of capacity, or is there something else to check for?

Their electrolyte (Rubycon MFZ) starts to attack the foil / plates, making the cap unable to withstand the voltage that it is rated for. The leakage current also greatly increases. In some cases, this can cause the cap to short-circuit internally and then rupture. Or, if the cap sits unused for a long time, then the electrolyte will still consume the foil/plates, producing gas inside the can and make the cap vent eventually.
In either case, you can observe this on the cheap ESR meters when the capacity of the cap starts going close or above its tolerance - e.g. the 2700 uF Rubycon MFZ will often start reading above 3000 uF. Up to 3240 uF, the cap is still technically "in tolerance" (+20%). But whenever I see such known problematic series to start going above 15%, I know they are nearing EOL and bound to start bulging/leaking any day soon.

Over what time period was that?

Usually years apart.
At least that's more or less when I try to reform my pulled caps. New ones, I just reform briefly for a few minutes before installing, if they are NOS.

The three capacitors that i left reforming for about a day for longer than another three, (and then charging them all up to 6.2V together), have retained 4.4V, and the other three have retained 4.0V after about four days of being disconnected from the power supply

If the caps are very old *and* USED, then yes, you might notice a tiny difference if you leave them reforming for a day vs. just a few hours vs. just a few minutes.
Generally, when caps have been used in a circuit with a certain DC voltage level for a very long time, they kind of tend to have "permanently" reformed to that voltage level and will take a very long time (days) to reform them to a new (higher) voltage level and stay that way.

(both sets of caps had no observable DC leakage current greater than 0.0000V at 6.2V - as i was thinking that leaving them refoming for a longer than suggested period, at max voltage, might not be good for them)

I think that's the takeaway here in this thread: as long as the leakage current is within norms while reforming the cap, then it should be fine to put in a circuit.