How to Recondition (Reform) Electrolytic Capacitors and Why

[Topcat]

^
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]

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]

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]

Originally Posted by eccerr0r

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]

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

[Per Hansson]

Originally Posted by eccerr0r

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]

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]

^ 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]

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]

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.