How to Recondition (Reform) Electrolytic Capacitors and Why

[eccerr0r]

How about this food for thought...

Do bipolar/nonpolar electrolytic capacitors need to be reformed and how would this be done?

[eccerr0r]

450V, 100µF NP capacitor ... reform?

[Per Hansson]

Of course it will have a oxide layer like any other electrolytic capacitor so why not?
Basically internally non-polar capacitors are two capacitors connected in series.
I would reform it "both ways" i.e, switching polarity after the first side is done.
This is just my "feeling" though

[eccerr0r]

the old capacitor is really leaky when trying to reform it according to the sencore, probably time to pitch it? hmm...

[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).