J
Jim Adney
Guest
We have a disagreement at work regarding the actual operating
principle behind an aluminum electrolytic capacitor. While we agree
that the capacitance is in the aluminum oxide (alumina) layer that is
formed on one foil, and the electrolyte serves as a conductor between
the oxide layer and plain foil strip. Beyond that there is a slight
difference in viewpoints in the details.
I'll try not to give away which viewpoint is mine.
1) The alumina layer is the capacitor and the insulator. When we
reform an old electrolytic that has become leaky we are just creating
new oxide in places where the old layer had deteriorated with time and
lack of a voltage source to maintain the oxide.
2) The alumina is a sponge which is filled with the conductive
electrolyte. When a capacitor is first formed, current thru the
electrolyte electrolyzes some of the aqueous electrolyte and a very
small amount of hydrogen forms tiny bubbles within the alumina matrix.
Once these bubbles have filled sufficient spaces in that matrix there
will no longer be current between the 2 foils. When you reform an old
capacitor you're just renewing the supply of H2 bubbles in the alumina
until the leakage gets small again.
-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------
principle behind an aluminum electrolytic capacitor. While we agree
that the capacitance is in the aluminum oxide (alumina) layer that is
formed on one foil, and the electrolyte serves as a conductor between
the oxide layer and plain foil strip. Beyond that there is a slight
difference in viewpoints in the details.
I'll try not to give away which viewpoint is mine.
1) The alumina layer is the capacitor and the insulator. When we
reform an old electrolytic that has become leaky we are just creating
new oxide in places where the old layer had deteriorated with time and
lack of a voltage source to maintain the oxide.
2) The alumina is a sponge which is filled with the conductive
electrolyte. When a capacitor is first formed, current thru the
electrolyte electrolyzes some of the aqueous electrolyte and a very
small amount of hydrogen forms tiny bubbles within the alumina matrix.
Once these bubbles have filled sufficient spaces in that matrix there
will no longer be current between the 2 foils. When you reform an old
capacitor you're just renewing the supply of H2 bubbles in the alumina
until the leakage gets small again.
-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------