[volt-nuts] Capacitor measurement
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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