Re: Cap voltage - time

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 2/20/01 10:43:18 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes: 


>
> Original poster: "kevin wilson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <
>
> thebiggiantkevin-at-hotmail-dot-com> 
>
> Could someone please give me the equation to find a caps exact voltage 
> after 
> a given charge time? Probably a basic equation, but I cant find it 
> anywhere. 
> Thanks 



I think the equation you are looking for might be: 
Vc=Vmax(1-exp(-t/RC)) 
where Vc is voltage on the cap, Vmax is the applied voltage, t is in seconds, 
R is total resistance of circuit in Ohms, and C is capacitance in Farads. 
This is when charging a cap from a constant voltage. For a varying input 
voltage, things get much more complex, but if 1/4f >> t/RC I believe it will 
work fairly well for the initial charging from an AC line also. 
Matt D.