On Saturday 25 February 2006 19:23, Bill Sloman wrote: >At 23:01 25-2-2006, you wrote: >>On Feb 25, 2006, at 1:39 PM, Karel Kulhavy wrote: >>>What does it mean? That the capacitor loses capacity when switching >>>between charge and discharge? >> >>Yes. If you start with your 2.2 µf capacitor discharged, charge it up >>to a volt, it might take the full 2.2 µC it's supposed to. But then >>discharge it to zero volts, you might only get 2.1 µC back! The >>charge doesn't disappear (averaged over many cycles the net DC >>current will be zero), but in general when you push charge in with >>voltage, the capacitor pushes back with less voltage when it's >>discharging. That's a net energy loss to the circuit, dissipated as >>heat. A "Q meter" will register this as resistance, but it's not >>ohmic, and may not have the same effect as ohmic resistance on >>circuit operation. > >Put on pedant hat. > >Charge is conserved - if you could convert >electrons to heat, you could fry your circuit, >and eliminate our dependence on oil. > >Remove pedant hat. > >What you are talking about here is "charge soak" >which is often modelled as extra >capacitance-plus-series-resistance in parallel >with the ideal capacitor you thought you were >buying. I've seen time constants varying from a >few seconds to a number of minutes, depending on >what I was doing. The charge is still in the >capacitor, but it's coming out slowly.
Its called dielectric absorbsion in my field as a CET. In some glasses commonly used for crt (picture tubes) envelopes, you can add several years to the phenomenon. I was recently tapped pretty hard by a monitor crt whose scan transformer and its ability to generate high voltage failed a good 5 years ago. And once many years ago, I hung a clip lead from the anode connector to the spring in contact with the dag coating on the outside of the tube, and a week later I could lift the clip, leave it away from the anode connector for several minutes, and still get a 1/4" spark as I reconnected it. I think the clip lead was still on it when I turned it in for dud credit several weeks later. -- Cheers, Gene People having trouble with vz bouncing email to me should add the word 'online' between the 'verizon', and the dot which bypasses vz's stupid bounce rules. I do use spamassassin too. :-) Yahoo.com and AOL/TW attorneys please note, additions to the above message by Gene Heskett are: Copyright 2006 by Maurice Eugene Heskett, all rights reserved.
