🚀 go-pugleaf

zowie@daedalus.stanford.edu (Craig "Powderkeg" DeForest) writes:

> What was probably going on is that you were charging the capacitor with 
> your ohm-meter.  The way most ohm-meters work is to apply a voltage across
> the contacts, and measure the current through 'em.  That's why, on most 
> analog multi-meters, the resistance scale is backward from the current: 
> because the ohm-meter setting is really an ammeter, with a calibrated
> voltage across the leads.  The more current, the less resistance.
> 
> By trying to measure the capacitor, you were probably stuffing charge
> into it, causing the time integral (above) to go up.  The rest of the time,
> the capacitor just stored the charge, holding its voltage until you tried
> to measure again.
> 
> One way to check this is to attach your ohmmeter to the capacitor and
> hold it there.  It should charge up in a few seconds to a minute.
> --
> Craig DeForest -- astrophysicist for hire: (415) 723-3216         1-line sig!


Craig,

        If I read his post correctly, he was measuring voltage 
using the voltage scale on a digital multimeter (imput impedance 
of greater than 10 megohm) which would preclude the ability for 
the meter to charge the capacitor.  Now if you are right, that he 
was set at the ohm scale, he would be instilling a charge, but it 
would be very slight with a digital meter, and would take months 
to charge up a (70,000 microfarad?) capacitor (I don't remember 
the exact value, but it was a biggie).  If I remember right, it 
was stated that he was measuring voltage- and I made a previous 
statement as to how and why electrolytics behave that way.  All of 
us in physics and electronics are aware of this principle- as all 
of us have been nailed by HV electrolytics at one time or another.

sq