# Capacitive Reactance formula with DC applied

Discussion in 'General Electronics Chat' started by massive, May 17, 2010.

1. ### massive Thread Starter Member

May 7, 2010
20
2
Hi,

If DC is applied to a capacitor , can the Xc formula also apply, minus the " frequency " component ..??

Xc = 1 /(2*pi*f*C ) , remove f , becomes ; Xc = 1 /(2*pi*C ) ,

for DC , presenting an open circuit at maximum Ohms .
Ive calculated some μF measurements and they come out ,way into the MegOhm range ,so is it normal to utilise this idea ?.

2. ### Bychon Member

Mar 12, 2010
469
41
The frequency still applies, and it is zero.

and, No, it is not normal to utilize faulty formulas.

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3. ### dsp_redux Active Member

Apr 11, 2009
182
5
In DC, you suppose the frequency to tend towards 0. Knowing that,
$X_C = \frac{1}{2\pi f C} |_{f\rightarrow 0} = \infty$
That's why in a DC analysis, you can pretend that capacitors are open-circuits.

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