RE: Some capacitor questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Chris Sartler by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Chris.Sartler-at-adicon-dot-com>

<What is the difference between pF uF, and the others? If there was just a
site that tells conversions, that is all I would need, since I know what
Pico, micro and the lot mean.>

 uf stands for micro farads it is some number to the x 10^-6 
nf(less common) stands for nano farads it is some number to the x 10^-9
pf stands for Pico farads it is some number to the x 10^-12

This is standard engineering format. So for example if you have a 20uf cap
it would be 20 x 10^-6f or in decimal format  .000020f   this would relate
to 20000nf or 20000000pF.  in the reverse direction if you have a 40pf cap
you will have a .000000000040f cap or a .040nf or a .000040uf cap.  

<I see how capacitors do their job, but I don't understand how they are
charged by weaker power sources and how they get discharged in a circuit.>

Capacitors are energy storage devices, similar to a battery.  They store
charge on their plates, initially a capacitor has no charge it is in a
discharged state, i.e. where there is no potential difference across the
plates.  They can store .002V or 20000V (Of course depending on their WV
ratings)it depends on what voltage the source is charging them at unless Vs
(voltage of the source) is exceeding the WV(working voltage).

<Also, what makes some capacitors discharge all their energy at once, or
slowly over time?>  

The total impedance of the load and the internal resistance of the
capacitor. If you took a 20uf cap and charged it to 25 V and put a 25ohm
resistor across it would discharge quickly. Now with that same cap take a
100kOhm resistor across it and it will discharge slower.  One step further
take the capacitor charge it and then let it sit on the table it will
eventually bleed off the charge but will take longer than the 25 ohm or the
100k ohm resistor (note the load is not the air gap in this example, but the
plate conductance).  

Be careful however capacitors can have "memory" especially high voltage caps
like the ones used in tesla coils.  Capacitive memory is the rebulding of
charge after the cap has been discharge, with no additional source voltage
connected.  Always Discharge high voltage caps through a bleader resistor
and leave them tied togeather through that resistor when not in use!

Hope this helps,
Chris

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, October 19, 2001 8:07 AM
To: tesla-at-pupman-dot-com
Subject: Some capacitor questions


Original poster: "bdsabds sadgsdgsda by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <fdgahbdfhbfdb-at-juno-dot-com>

Thanks,
Jon
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