RC Time Constant

[panfilero]

How do you figure out the RC time constant of a battery in series with a resistor that is in series with the parallel combination of a capacitor and resistor? (Basically a low pass RC filter with a resistor in parallel across the output cap)

battery ---> R1 ----> (C1||R2)

I would think that the RC time constant would only involve the resistor in series with the battery (R1)... and if I were to disconnect the battery, then the capacitor would discharge through the resistor that is in parallel with it (R2).

so RC Time Constant = R1C1 ?

Does the resistor in parallel with the cap play a role in the RC time constant when it's charging?

 

[Rich Webb]

On Fri, 27 Jul 2012 07:47:03 -0700 (PDT), panfilero
<panfilero@gmail.com> wrote:

How do you figure out the RC time constant of a battery in series with a resistor that is in series with the parallel combination of a capacitor and resistor? (Basically a low pass RC filter with a resistor in parallel across the output cap)

battery ---> R1 ----> (C1||R2)

I would think that the RC time constant would only involve the resistor in series with the battery (R1)... and if I were to disconnect the battery, then the capacitor would discharge through the resistor that is in parallel with it (R2).

so RC Time Constant = R1C1 ?

Does the resistor in parallel with the cap play a role in the RC time constant when it's charging?

Sounds like a question for M. Thévenin.

--
Rich Webb Norfolk, VA

 

[krw@att.bizzzzzzzzzzzz]

On Fri, 27 Jul 2012 07:47:03 -0700 (PDT), panfilero <panfilero@gmail.com>
wrote:

How do you figure out the RC time constant of a battery in series with a resistor that is in series with the parallel combination of a capacitor and resistor? (Basically a low pass RC filter with a resistor in parallel across the output cap)

battery ---> R1 ----> (C1||R2)

I would think that the RC time constant would only involve the resistor in series with the battery (R1)... and if I were to disconnect the battery, then the capacitor would discharge through the resistor that is in parallel with it (R2).

so RC Time Constant = R1C1 ?

Does the resistor in parallel with the cap play a role in the RC time constant when it's charging?

Yes, the time constant is the parallel combination of the two resistors times
the capacitor. Don't forget to use the voltage divider equation to calculate
the terminal voltage (and voltages at the times inbetween).

 

[Helmut Sennewald]

----- Original Message -----
From: "panfilero" <panfilero@gmail.com>
Newsgroups: sci.electronics.basics
Sent: Friday, July 27, 2012 9:37 PM
Subject: Re: RC Time Constant


On Friday, July 27, 2012 10:35:54 AM UTC-5, Rich Webb wrote:

On Fri, 27 Jul 2012 07:47:03 -0700 (PDT), panfilero





How do you figure out the RC time constant of a battery in series with a
resistor that is in series with the parallel combination of a capacitor
and resistor? (Basically a low pass RC filter with a resistor in parallel
across the output cap)



battery ---> R1 ----> (C1||R2)



I would think that the RC time constant would only involve the resistor
in series with the battery (R1)... and if I were to disconnect the
battery, then the capacitor would discharge through the resistor that is
in parallel with it (R2).



so RC Time Constant = R1C1 ?



Does the resistor in parallel with the cap play a role in the RC time
constant when it's charging?



Sounds like a question for M. Thévenin.



--

Rich Webb Norfolk, VA

Doh! Absolutely right! thanx.

which leads to RC = (R1+R2)*C


Hello,

Sorry, your given formula is wrong.

Take a look from the capacitor's view into the circuit while assuming the
battery has zero Ohm resistance.
Now you will see R2 parallel R1.

tau = C*R1*R2/(R1+R2)

Best regards,
Helmut

 

[panfilero]

On Friday, July 27, 2012 10:35:54 AM UTC-5, Rich Webb wrote:

On Fri, 27 Jul 2012 07:47:03 -0700 (PDT), panfilero





How do you figure out the RC time constant of a battery in series with a resistor that is in series with the parallel combination of a capacitor and resistor? (Basically a low pass RC filter with a resistor in parallel across the output cap)



battery ---> R1 ----> (C1||R2)



I would think that the RC time constant would only involve the resistor in series with the battery (R1)... and if I were to disconnect the battery, then the capacitor would discharge through the resistor that is in parallel with it (R2).



so RC Time Constant = R1C1 ?



Does the resistor in parallel with the cap play a role in the RC time constant when it's charging?



Sounds like a question for M. Thévenin.



--

Rich Webb Norfolk, VA

Doh! Absolutely right! thanx.

which leads to RC = (R1+R2)*C

 

[panfilero]

On Friday, July 27, 2012 3:38:20 PM UTC-5, Helmut Sennewald wrote:

----- Original Message -----


Newsgroups: sci.electronics.basics

Sent: Friday, July 27, 2012 9:37 PM

Subject: Re: RC Time Constant





On Friday, July 27, 2012 10:35:54 AM UTC-5, Rich Webb wrote:

On Fri, 27 Jul 2012 07:47:03 -0700 (PDT), panfilero











How do you figure out the RC time constant of a battery in series with a

resistor that is in series with the parallel combination of a capacitor

and resistor? (Basically a low pass RC filter with a resistor in parallel

across the output cap)







battery ---> R1 ----> (C1||R2)







I would think that the RC time constant would only involve the resistor

in series with the battery (R1)... and if I were to disconnect the

battery, then the capacitor would discharge through the resistor that is

in parallel with it (R2).







so RC Time Constant = R1C1 ?







Does the resistor in parallel with the cap play a role in the RC time

constant when it's charging?







Sounds like a question for M. Thévenin.







--



Rich Webb Norfolk, VA



Doh! Absolutely right! thanx.



which leads to RC = (R1+R2)*C





Hello,



Sorry, your given formula is wrong.



Take a look from the capacitor's view into the circuit while assuming the

battery has zero Ohm resistance.

Now you will see R2 parallel R1.



tau = C*R1*R2/(R1+R2)



Best regards,

Helmut

agreed. thanx