charging a capacitor from a solar cell? Need help!

[Bumper]

I'm working on a project for school and want to set up a solar cell to
charge up a couple of really big (size of a soda can) capacitors and then
once they are charged have a relay or something close and send the power
stored in the capacitors to a small electric gear motor.

The idea is that the solar cell doesn't have enough output to power the
motor continuously but if it charges the capacitors up over a period of
time until there is enough current to run a small motor for a few
seconds.

Any ideas?

Thanks, Bill

 

[Charles]

"Bumper" <sales@dakotaairparts.com> wrote in message
news:473eaf95$0$20564$4c368faf@roadrunner.com...

I'm working on a project for school and want to set up a solar cell to
charge up a couple of really big (size of a soda can) capacitors and then
once they are charged have a relay or something close and send the power
stored in the capacitors to a small electric gear motor.

The idea is that the solar cell doesn't have enough output to power the
motor continuously but if it charges the capacitors up over a period of
time until there is enough current to run a small motor for a few
seconds.

http://www.mpoweruk.com/alternatives.htm

You can charge up a so-called super capacitor via a photovoltaic panel.

Some panels might have over-current protection, which could be a problem. A
discharged super capacitor is going to be a high-current load. As the
charge builds up, the charging current will decay exponentially.

 

[default]

On Sat, 17 Nov 2007 04:08:37 -0500, Bumper <sales@dakotaairparts.com>
wrote:

I'm working on a project for school and want to set up a solar cell to
charge up a couple of really big (size of a soda can) capacitors and then
once they are charged have a relay or something close and send the power
stored in the capacitors to a small electric gear motor.

The idea is that the solar cell doesn't have enough output to power the
motor continuously but if it charges the capacitors up over a period of
time until there is enough current to run a small motor for a few
seconds.

Any ideas?

Thanks, Bill

Google for "beam bots" or "beam robots," That is what they do. Use a
solar cell or two charge a cap until a threshold voltage is reached
then dump the power into the motors to move the robot.

Check out this to get started:
http://www.beam-wiki.org/wiki/index.php?title=1381-based_Solar_Engines

Physical size of the cap is not a good indicator of storage capacity.
Large caps can just be old stock with low density technology, or high
voltage caps, or "fakes" - There are a few "computer grade" caps
around that have large external cans but inside are small caps - done
only to preserve the mountings and make them easy to change.

BTW "size of a soda can" isn't big unless you are designing cell
phones . . . If you were designing high power Tesla coils that would
be tiny indeed.

The microfarad rating is what counts for storage capacity. Some of
the beam bot folks use up to a farad of storage (size of a thick
quarter).
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