[sdiy] Polarized VS non-polarized electrolytic caps

[Harry Bissell]

Robin:

I found this... I have seen some bipolar electrolytics that were indeed two divices in the same can. This article seems to indicate
that either way is possible...

http://electrochem.cwru.edu/encycl/art-c04-electr-cap.htm

its from
Sam Parler
Cornell Dubilier Electronics, Inc.
140 Technology Place
Liberty, SC 29657, USA
E-mail: sparler at cde.com
(March, 2005)

<snip>

"Non-polar (or bi-polar) devices can be made by using two anodes instead of an anode and a cathode, or one could connect the positives or negatives of two identical device together, then the other two terminals would form a non-polar device."

H^) harry


----- Original Message -----
From: Robin Whittle <rw at firstpr.com.au>
To: synth-diy at dropmix.xs4all.nl
Cc: ganesha <goaqihai at yahoo.co.uk>, Harry Bissell <harrybissell at wowway.com>
Sent: Sat, 21 Jan 2012 08:10:09 -0500 (EST)
Subject: Re: [sdiy] Polarized VS non-polarized electrolytic caps

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/



-- 
Harry Bissell & Nora Abdullah 4eva