I would like to know how to calculate capacitor discharge time.
EC=IT
E x C = I x T
Voltage times Capacitance = Current times Time
The max voltage across the capacitor is 7 V (9 V battery minus the LED Vf)
C = (I x T) / E
C = (.02 x 3) / 7.0 = 0.0086 = 8600 uF
The resistor is calculated using Ohm's Law.
R=E/I
Resistance = Voltage divided by Current
R = 7 / 0.02 = 350 ohms
Explains how to find the capacitor needed to discharge the voltage threw the LED. I got that.. But how do I find out how long it will take for a capacitor, resistor to discharge the voltage?
Like for instance, this guy..
His parts.. 1000uF, or 0.001F Capacitor, 9v battery, and a 22k Ohm Resistor. The LED is red, which means it's 0.02A (20mA), and has a forward voltage of 2Vdc.
Finding the resistor for the LED.
9Vs - 2Vf = 7.0RVd
R = 7RVd / 0.02If = 350Ω
But I'm lost.. How do I figure out how long the LED will stay lit..? I know how to find the capacitor value for the RC Circuit I have.. But I don't know how to find how long the LED will stay lit, if I have a capacitor, and know the values of the component.
He says in the comments, that it will still be lit, even after 10 minutes.. Wouldn't you need a higher capacity capacitor to do stuff like that?
10 Minutes x 60 Seconds = 600 Seconds.
0.02A x 600 = 12
C = (0.02A (If) x 600s) = 12 / 7Vdc (Vf) = 1.71 Farads !!!!
That's EXPENSIVE !!! But he's not using a 1.71 Farad capacitor.
http://www.mouser.com/ProductDetail/Cornell-Dubilier/DCMC175U16FG2D/?qs=zv9oXRM5khgxb9WM9DbwmA==
It's $141.55 for a 1.7 Farad capacitor.
EC=IT
E x C = I x T
Voltage times Capacitance = Current times Time
The max voltage across the capacitor is 7 V (9 V battery minus the LED Vf)
C = (I x T) / E
C = (.02 x 3) / 7.0 = 0.0086 = 8600 uF
The resistor is calculated using Ohm's Law.
R=E/I
Resistance = Voltage divided by Current
R = 7 / 0.02 = 350 ohms
Explains how to find the capacitor needed to discharge the voltage threw the LED. I got that.. But how do I find out how long it will take for a capacitor, resistor to discharge the voltage?
Like for instance, this guy..
His parts.. 1000uF, or 0.001F Capacitor, 9v battery, and a 22k Ohm Resistor. The LED is red, which means it's 0.02A (20mA), and has a forward voltage of 2Vdc.
Finding the resistor for the LED.
9Vs - 2Vf = 7.0RVd
R = 7RVd / 0.02If = 350Ω
But I'm lost.. How do I figure out how long the LED will stay lit..? I know how to find the capacitor value for the RC Circuit I have.. But I don't know how to find how long the LED will stay lit, if I have a capacitor, and know the values of the component.
He says in the comments, that it will still be lit, even after 10 minutes.. Wouldn't you need a higher capacity capacitor to do stuff like that?
10 Minutes x 60 Seconds = 600 Seconds.
0.02A x 600 = 12
C = (0.02A (If) x 600s) = 12 / 7Vdc (Vf) = 1.71 Farads !!!!
That's EXPENSIVE !!! But he's not using a 1.71 Farad capacitor.
http://www.mouser.com/ProductDetail/Cornell-Dubilier/DCMC175U16FG2D/?qs=zv9oXRM5khgxb9WM9DbwmA==
It's $141.55 for a 1.7 Farad capacitor.