[volt-nuts] Capacitor measurement

Mark Sims holrum at hotmail.com
Tue Mar 16 22:22:43 UTC 2010

Speaking of capacitor measurement...  I am building a capacitive discharge spot welder/cutter similar to the ones at http://ultrakeet.com/index.php?id=article&name=cdWelder_p2 and http://frikkieg.blogspot.com 

I went down to the local electronics emporium and bought a 1.5 farad 0.002 ohms ESR car audio cap,  took it home,  and did some measuring.   Turns out the capacitance was 0.15F and the esr was .026 ohms.   A second sample had the same value (ESR was .0065 ohms).   Utter ripoff!  Also the capacitor can was about 1/3 empty.

I also tested some heavy gauge car audio cables for the store owner.  BEWARE,  some of the audio cable suppliers are up to similar shenanigans.  A 4 AWG cable that looked like copper was plated aluminum (1.5 times the resistance of copper).  8 and 10 AWG cables were some mystery metal...  3 times the resistance of copper (but not magnetic).  All were made in China (as were the caps).

One bright spot was a piece of Made in the USA pure oxygen free copper 10 AWG cable.  It measured over 20% better conductance than one would expect from pure copper!  Looks like it is a little fatter than 10 AWG.  Two strands of that 10 AWG wire  has less resistance than the 4 AWG aluminium stuff. 		 	   		  
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