On Mon, 5 Aug 2002, =C5ke Neehr wrote:

>Hello!
>
>I need help with the calculation
>of the time of charge and discharge
>for a BackUp capacitor 0,1 uF 5,5 V

C =3D Q/U =3D I*t/U

F.ex. assuming 0.1F 5.5V and start voltage=3D5V, end=3D3V, current=3D20uA=
  (=3D2 *
10^-5A) we have time:

t =3D C*U/I =3D 0.1 * (5-3) / ( 2 * 10^-5) =3D 1 * 10^4 seconds or just s=
hort
of a week.

The charge time is determined by the capacitor construction and the power
supply. Usually it takes up to 100mA when empty, and can be considered
charged after 1/2 hour at 5V nominal. This assuming it is a supercap.

Peter

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