hancock4@bbs.cpcn.com wrote:   
   > On Tuesday, June 17, 2014 2:40:12 PM UTC-4, mrob...@att.net wrote:   
   >> Around that time, improved materials and manufacturing started   
   >> allowing for physically smaller capacitors that have a decent amount   
   >> of energy storage.   
   >   
   > Side note about capicitor size:  Landline telephone sets have always   
   > had a capcitor to separate the 20 Hz ringing current from the 48V DC   
   > signal and talk power.   
      
   Well, 48 V at the exchange.  Maybe 5 V by the time it gets all the way   
   out to your off-hook telephone.  :)   
      
   > Many years ago the capacitor to do this was so large that the ringer   
   > unit required a box separate from the telephone set.  In 1938 they   
   > reduced the size enough to fit it all in a "combined" set (the WE 302   
   > or AE 40).  Even then the capictor was still the size of a hot dog.   
   > In 1950 they reduced it again and placed it, with other components,   
   > into a roughly 1" cube (the classic WE 500 set).   
      
   It's pretty much the same process for "big" capacitors.  A cheap tube   
   radio in the 1940s and 1950s would have a main power supply capacitor of   
   between 50 to 100 uF at 150 V, and it would be the size of a roll of   
   quarters.  Today, it isn't hard to buy a 1000 uF, 400 V capacitor that   
   fits in the same space.   
      
   These same kinds of improvements are what have made capacitors   
   interesting for energy storage in traction.   
      
   Matt Roberds   
      
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