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Electronics => Electronics => Topic started by: Dudekiller on March 23, 2009, 07:20:09 AM

Title: Charging and discharging a Capacitor
Post by: Dudekiller on March 23, 2009, 07:20:09 AM

I had an idea of creating my own rechargeable power supply. I tried to create a test experiment in which I attach a 9 volt battery to a 1000uf capacitor for a minute then let the capacitor discharge turn on a LED. However, the discharge time is the same. Can anyone suggest ways in which I can increase the discharge time?

Title: Re: Charging and discharging a Capacitor
Post by: airman00 on March 23, 2009, 07:58:57 AM

resistor

Title: Re: Charging and discharging a Capacitor
Post by: want2learn on March 23, 2009, 02:12:45 PM

Have you googled BEAM SOLAR ENGINES?

Title: Re: Charging and discharging a Capacitor
Post by: Soeren on March 23, 2009, 03:21:51 PM

Hi,

Quote from: Dudekiller on March 23, 2009, 07:20:09 AM

I had an idea of creating my own rechargeable power supply. I tried to create a test experiment in which I attach a 9 volt battery to a 1000uf capacitor for a minute then let the capacitor discharge turn on a LED. However, the discharge time is the same. Can anyone suggest ways in which I can increase the discharge time?

Increase capacitance and/or voltage and/or decrease discharge current - sorry, no such thing as a free meal.

The formula for capacity is C=A*s/V
Where:
C is capacity in Farad
A is Current in Ampere
s = time in seconds
V=the voltage drop allowed in the s seconds

Say you wanna supply a red LED (through a resistor) 10mA (start current) for 20 seconds with a 9V battery.
A resistor of 680 Ohm should be series connected with the LED.
If you determine 5mA as the end goal (after the 20 seconds), the end voltage on the cap should be 5.3V.

Now stuff those numbers into the formula to find the value of the capacitor needed:
C = 0.01A*20s/(9-5.3) = 54mF = 54,000µF.