Re: Mot DC Ps

["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 2/17/01 4:15:15 PM Eastern Standard Time, tesla-at-pupman-dot-com 
writes: 


>
> I have a question too when you discharge a cap though a resistance for a 
> certain value of R you have an oscillating circuit (because of parasitic 
> inductance ), if you increase the value of R to a certain point the cap 
> will just discharge whit out oscillation how do you calculate this 
> value. 
>
> Tx 
> Luc Benard 



Hi Luc 
        The critical point is at R=2*sqrt(L/C). If R is greater than this 
value, no oscillation takes place. The frequency equation f=1/((2pi*sqrt(LC) 
is actually a simplifications of: 
F=sqrt(1/LC-(R/2L)^2)/2pi 

This follows from the circuit current as a function of time being: 

        I(t)=Vo/Lw * exp(-at) * Sin(wt), where a=R/2L and 
w=sqrt((1/LC)-(R/2L)^2) and Vo is the initial voltage on the capacitor. 

If you need a complete derivation of this, write me on or off list. 

Matt D.