F to mAh?

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#1
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Hello again dear Freaks!

I have a application that I thinking of replacing the battery with a supercap. How can I calculate from Farad to milliAmphours?

Best regards
Björn

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The relationship is quite staright forward integral expression

i = {Cdv/dt where { represents the integral symbol

lets assume the application is going to draw a fairly steady current
then

I = C deltaV/deltaT where deltaV is acceptable drop in capacitor terminal voltage and deltaT is the time it will take to achieve that drop.

From here on we can say the equivalent miliAmphour rating is C*deltaV.

Hope this gives You some idea of available tradeoffs of super cap value versus its voltage rating versus Your voltage needs etc etc etc

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Hii ...

i think u can calculate the mAh this way :-

Q = C x V (C= capacitor rating , V = voltage on its terminals)
Q = Charge (Amp Sec) .. so Q x 1000/3600 = mAh

Regards

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bjornhi,

Short answer:
With a 1 volt change in output voltage (for example if you charge it to 5 volts and your circuit works when the voltage drops to 4 volts), a 1 Farad capacitor will give 277 microamp-hours.

The relationship is linear. 10 Farads gets you 2.77 milliamp-hours, etc.

--
"Why am I so soft in the middle when the rest of my life is so hard?"
-Paul Simon

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From physics class we remember that charge equals current multiplied by time, so Q=I*t. We also know that charge equals capacitance multiplied by voltage, so Q=C*U.

Q=I*t=C*U => I*t=C*U, move U to left side, you get C=I*t/U.

- Jani