Printable View
I am designing a project based on nano-Watt PIC like the 12F683. It is going to be powered by a supercap of 1Farad and I want to calculate the time it will work on the cap. The data are:
Working voltage: 4.2 to 2.5 Volts
Capacitor: 1 Farad
Current: 208 micro amps
As this needs Integration to calculate the time the cap lasts, I am little confused. Can anyone help me with this?
I came up with the equation in the attached file. Is it correct?
Thanks,
Ioannis
Hi, Ioannis
Q ( Coulombs ) = I (A ) * t ( s )= C ( F ) * U ( V )
...
( 4.2 - 2.5 ) * 1 = 208 E-6 x t
>> t = 8173 s ...
That's all !
Nice general equation, indeed ... may I laugh a little ???
If your current draw was constant ... but just have a look to the curves at the end of the datasheet ...
You'll have some extra time !!!
BUT you must take into account the Supercap self discharge current ....
A look at the datasheet ... shows .... 315 µA ( Horror !!! )
http://www1.produktinfo.conrad.com/d...n-Gold-Cap.pdf
So, You'll have some minus time ...
1.7 / ( 208 + 315 ) E-6 = 3250 Sec ...
Just hope an hour !!!
Alain
Hi Alain.
Thanks for the reply. I was not too rusty after all!
Be well my friend and thanks again.
Ioannis