[ARC5] Testing Caps

[Robert Eleazer]

I decided to try out a transformer pulled out of a junked AM/FM stereo to see if it would make a good 28VDC power supply.  It has a nice big 64VCT secondary winding.  I hooked up a couple of 3 amp 1000 PIV diodes and a 8200 mfd cap out of another junked piece of gear.

I was astonished to see I got only 29 VDC under no load.  Putting a 100 ohm power resistor as the load dropped it to 28.3 VDC. 

Today I used two new diodes and an unused 6400 mfd with the transformer and got the expected 44VDC.  

Now the strange part is that the junker 8200 mfd cap I charged up to 50 VDC and found it would still have 43 VDC on it days later.  But with the new 6400 mfd cap when disconnected from the circuit  the voltage drops right off immediately.

I have assumed that the length of time a cap would hold a charge is an indicator of its usefulness - but maybe not?

Wayne
WB5WSV     

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