### Author Topic: Charging and discharging a Capacitor  (Read 1022 times)

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#### Dudekiller

• Jr. Member
• Posts: 33
##### Charging and discharging a Capacitor
« 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?

#### airman00

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• Supreme Robot
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• narobo.com
##### Re: Charging and discharging a Capacitor
« Reply #1 on: March 23, 2009, 07:58:57 AM »
resistor
Check out the Roboduino, Arduino-compatible board!

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#### want2learn

• Robot Overlord
• Posts: 189
##### Re: Charging and discharging a Capacitor
« Reply #2 on: March 23, 2009, 02:12:45 PM »
Have you googled BEAM SOLAR ENGINES?

The question that drives me hazy:

Am I, or the others crazy?

#### Soeren

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##### Re: Charging and discharging a Capacitor
« Reply #3 on: March 23, 2009, 03:21:51 PM »
Hi,

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.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?