capacitor charging and discharging

Thread Starter

Paul McD

Joined Feb 9, 2012
I've got an electrical problem with capacitors:

I need to make a circuit for a solar car and I've been given a 10F capacitor, a motor and I can use other components if needs be. I need to be able to charge the 10F capacitor with a 3V solar panel, disconnect the solar panel, turn a switch and run the motor. I've tried to make a circuit on copper strip board but without success. I'd be extreamely gratefull on any assistance in charging and discharging capacitors. A circuit diagram would be perfect.

Many Thanks.


Joined Oct 23, 2010
As a good starting place please show us what circuit you tried so we can help you build on that or give constructive suggestions based on what you did. It will help a lot.

Thread Starter

Paul McD

Joined Feb 9, 2012
Attached is the circuit that I tried, but I couldn't get any output.

Hope this is useful?

I could do with a response promptly as I need to have the circuit built soon.




Joined Dec 28, 2011
The first problem that I see is that your capacitor has no path to discharge its energy. When you close the switch all you are doing is connecting the + side of the motor to ground. Try it the way I have edited your drawing. :)




Joined Oct 2, 2009
You need to provide some specifications on the motor. I don't think there is enough energy stored in the capacitor to run the motor unless it takes 1mA or less.


Joined Feb 7, 2012
In theory a 10F cap has 30 Coulombs of charge at 3V.
A coulomb is 1 amp for 1 second.
If the motor is say 0.5 amp (at 3v) then max of 60 seconds. BUT....
As the cap discharges the voltage will fall off, quite rapidly.
On the good side is, once the motor is moving the sustaining current can be relativly low. But if voltage falls to much it will stop.

Thread Starter

Paul McD

Joined Feb 9, 2012
Thanks very much for all your sugestions, but I'm affraid I don't know the specifications of the motor that was supplied, all I know is that I should be able to realistically use a 3v solar cell, a 10F capacitor and the provided motor. The specifications for the challenge say that I can have 15mins of charging time with the solar cell and should then be able to travel 8m, up to three times (fastest time wins).

If anyone can help more that would still be much appreciated.

Thanks very much for your help and kindness so far.
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