capacitor discharge time

[exxos]

Hi all,

If I have a 100uF capacitor charged to 12volts, then I place a 6R ressitor
across is (2amps) how long would it take to discharge to say 10volts ? How
do I work this out ?

Thanks,
Chris

 

[Bill Bowden]

"exxos" <exxos@home.co.uk> wrote in message news:<40f42499$0$6450$cc9e4d1f@news-text.dial.pipex.com>...

Hi all,

If I have a 100uF capacitor charged to 12volts, then I place a 6R ressitor
across is (2amps) how long would it take to discharge to say 10volts ? How
do I work this out ?

Thanks,
Chris

Subtract the voltage change (2) from the starting voltage (12)
and you get 10. Divide this by the starting voltage 10/12 and
you get 0.833. Find natural log of this and you get -0.182
Next, multiply by RC and you get -.182 *6 * 0.0001 = -.000109
Change sign to positive and the answer is 109 microseconds.

t = - log ((V-delta V)/V) * RC

t = - log ((12-2)/12) * .0006 = 109 uS

-Bill

 

[Mantra]

"exxos" <exxos@home.co.uk> wrote in message news:<40f42499$0$6450$cc9e4d1f@news-text.dial.pipex.com>...

Hi all,

If I have a 100uF capacitor charged to 12volts, then I place a 6R ressitor
across is (2amps) how long would it take to discharge to say 10volts ? How
do I work this out ?

Homework problem?

V = Vo exp(-t/RC)

 

[exxos]

"Mantra" <mymantra@yahoo.com> wrote in message
news:a6403f08.0407131653.39da3569@posting.google.com...

"exxos" <exxos@home.co.uk> wrote in message
news:<40f42499$0$6450$cc9e4d1f@news-text.dial.pipex.com>...
Hi all,

If I have a 100uF capacitor charged to 12volts, then I place a 6R
ressitor
across is (2amps) how long would it take to discharge to say 10volts ?
How
do I work this out ?

Homework problem?

Everyone always says this , actually , I've been in the electronis repair
trade for the past 15 years, unfortunatly working out stuff isn't by far in
my day to day role, and since I have a memory like a siv one tends to forget
over time

V = Vo exp(-t/RC)