Re: gEDA-user: ESR of 2.2u ceramic capacitor

[Gene Heskett <gene.heskett@xxxxxxxxxxx>]

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
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Copyright 2006 by Maurice Eugene Heskett, all rights reserved.