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Introduction

First of all, this question more like theorical rather than practical as I want to test my understanding about Aluminum Electrolytic Capacitor, which I will later called Al-Cap for short.

Preliminary knowledge

Manufacturing process.

First of all, le begin with manufacturing process of Al-Cap. the processes consist of following procedure.

  1. Roughten and preformed anode (positive) foil to increse surface area and pre made oxide layer.
  2. Cutting anode and cathode foil into desire size.
  3. winding, rolling anode, paper separator and cathode in to the cylindral form.
  4. Impregnation, apply electrolyte using vaccuum.
  5. Sealing, prevent electrolyte from leakage.
  6. Post forming or aging, apply voltage (CC/CV manner) with high temperature to heal imperfect dielectric layer or non forming area like curring edge. Improving self discharge rate.

Note: This website from capacitor manufacturer provide grate detail about these process website,

Theory or operation.

The anode foil and electrolyte act as electrode or plate like ordinary capacitor and oxide layer on anode foil act like dielectric. Combinding fact that the oxide layer is relatively thin and surface area of anode in increse by about factor of 200 due to rought surface, the Al-cap provide high capacitance campare to ordinary one. we need to use liquid electrode for cathode to match up the surface of anode. the cathode foil act like electrical contact point to electrolyte.

Reversing polarity

One of trade-off of electrolytic cap is that it polarize cap. inverse polarity can cause damage to the capacitor by dissolve anode's oxide layer lead to decreasing of break down voltage. As the resistance of electrolyte is very low, the capacitor become short circuit which product a lot of heat and pressure due to gas production from electrolysis reaction.

My assumption

As we can reforming capacitor which means there are oxide in the electrolyte. so if replicate those reforming condition by apply high temp and control voltage and current of inverse polarity supply. we can remove oxide layer from anode and form them on cathod instead then the capacitor is successfully reverese polarity.

Question

Q1. Is that possible to do so with my assumption procedure. Q2. If there are better or possible method please recommend and explain.

Expectation benefit

Whether this is possible or not, I hope this discussion raise awareness and understanding of operating principle of aluminum electrolytic capacitor. Personally I used to remembering that don't connect them in reverse polarity or majic smoke will appear but I never wonder why that such thing happen.

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  • \$\begingroup\$ How do you prevent the removal of the oxide layer in your reforming process as soon you apply reverse polarity? As that is exactly what happens in a regular electolytic cap if you apply reverse polarity. \$\endgroup\$
    – Janka
    Mar 3 at 9:34
  • \$\begingroup\$ @Janka the anode oxide layer will be removed in the process, however I hope that I can form the oxide layer on former cathode instead. For reverse polarity of regular electrolytic cap already explain in "Reversing polarity" section. In short, when the oxide layer was dissolve, the capacitor become short circuit then it heat up, generating gas and explode. \$\endgroup\$
    – M lab
    Mar 3 at 9:43

1 Answer 1

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Possibility? Yes.

Aluminium electrolytic capacitors do not necessarily just blow up if you get the polarity wrong. They might and what happens depends on the circuit they are in.

There are a lot of examples of products where capacitors are mounted with incorrect polarity and the circuit still works. For example some models of Commodore Amiga CD32.

I am sure I have read an application note from a capacitor manufacturer what happens if a capacitor is mounted incorrectly. There was some estimate on the effect of various degraded parameters such as loss of capacitance and higher ESR, so at least those capacitors could handle usage at wrong polarity at least once. Unfortunately, I could not find which application note it was and from which manufacturer.

The point just is that the capacitor starts to conduct a lot of current in reverse after it is being subjected to reverse voltage around 1..2V, so depending on the conditions, such as available current limiting, the process might happen too fast and too much pressure builds up and the capacitor vents or explodes, but if it happens slowly enough, the oxide layer starts to form and the capacitor will be somewhat degraded but will work with the new polarity.

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