[sdiy] Polarized VS non-polarized electrolytic caps

[Robin Whittle]

Hi Harry,

Do yo have any references for your dual capacitor explanation of
non-polar or bi-polar electrolytic capacitors?

I have never read an explanation, other than your's, but I can't imagine
that your two capacitors in series explanation is correct.  Firstly it
would be bulky and expensive. Secondly the two capacitors would need to
be isolated so their electrolytes did not meet.

The only way your explanation could work, I think, would be if one of
the capacitors developed an average DC voltage across it - whichever one
needed to in order that it had the correct polarity and the other
capacitor was not reverse biased.  For this to occur, DC current would
need to flow through the other capacitor - but this is not what
capacitors are supposed to do.

I always assumed that these capacitors have an electrolytically
deposited oxide on both plates, so both plates would have been acid
etched to create a very high surface area for this thin oxide layer.
Exactly how they generate this oxide, I am not sure.

I pulled apart an ELNA 3.3uF 10V "BI-POLAR" capacitor from the 70s or
80s.  Both plates have the same colour and texture, which is compatible
with my explanation.

  - Robin            http://www.firstpr.com.au/rwi/dfish/