help with kids science project

[sigpro2340]

Hi all
i'm new to the forum and need some help with my son's science fai
project that I thought was going to be a no brainer.

The project was a simple wind turbine to generate electricity to mayb
power a little led light or something. I read online we could use
little dc motor to do this...well yes it works but the blades do no
spin fast enough to make enough electricity to lite the lights righ
away.

So..i thought..why not run the motor to a set of rechargeable A
batteries then to a switch...and then to some little led lights. I
is the same idea as far as generating electricity..except it is bein
stored for later use.

But then i thought..if i wire the motor right to the batteries....wh
is to say the batteries wont keep powering the motor.

So basically...what i need help with is how to wire this...and wha
else do i need besides what i have which is

a 9-18v DC motor i think max is 18000 rp
2 AA batterie
some small 2 volt led light
a toggle switc

i know i'm going to need some sort of diode..but not sure what...thi
is where i need help...please!!!

Ro

 

[Rich Webb]

Hi all,
i'm new to the forum and need some help with my son's science fair
project that I thought was going to be a no brainer.

The project was a simple wind turbine to generate electricity to maybe
power a little led light or something. I read online we could use a
little dc motor to do this...well yes it works but the blades do not
spin fast enough to make enough electricity to lite the lights right
away.

So..i thought..why not run the motor to a set of rechargeable AA
batteries then to a switch...and then to some little led lights. It
is the same idea as far as generating electricity..except it is being
stored for later use.

But then i thought..if i wire the motor right to the batteries....who
is to say the batteries wont keep powering the motor.

So basically...what i need help with is how to wire this...and what
else do i need besides what i have which is:

a 9-18v DC motor i think max is 18000 rpm
2 AA batteries
some small 2 volt led lights
a toggle switch

i know i'm going to need some sort of diode..but not sure what...this
is where i need help...please!!!!

http://www.otherpower.com/toymill.html has a good explanation of the
what's and why's of this, along with some helpful advice.

Instead of lighting an LED (since LEDs are ubiquitous and one more LED
in the room at the fair will probably be a big shrug), consider going
with a couple of analog meters to show output voltage and current.
Much more visual appeal; things MOVE!

You (plural) will need to do a little research to find out what meter
ranges are appropriate. http://www.jameco.com is one convenient source
of analog meters; drill down in their menus though the tools & test
equipment menu into the "other meters" category.

 

[DecaturTxCowboy]

Coffee is still brewing, so I might have some errors and omissions here...

Hi all,
i'm new to the forum and need some help with my son's science fair
project that I thought was going to be a no brainer.

The project was a simple wind turbine to generate electricity to maybe
power a little led light or something. I read online we could use a
little dc motor to do this...well yes it works but the blades do not
spin fast enough to make enough electricity to lite the lights right
away.

So..i thought..why not run the motor to a set of rechargeable AA
batteries then to a switch...and then to some little led lights. It
is the same idea as far as generating electricity..except it is being
stored for later use.

But then i thought..if i wire the motor right to the batteries....who
is to say the batteries wont keep powering the motor.

So basically...what i need help with is how to wire this...and what
else do i need besides what i have which is:

a 9-18v DC motor i think max is 18000 rpm
2 AA batteries
some small 2 volt led lights
a toggle switch

Lets get a little of the specifications and math in line here first.

A small electric motor can be used as generator. Typically as a motor,
you'll see something like this:
6 volts in - 600 RPM - at 30 mA - with 10% efficiency
7 volts in - 1000 RPM - at 30 mA - with 20% efficiency
9 volts in - 2000 RPM - at 30 mA - with 30% efficiency
12 volts in - 3500 RPM - at 30 mA - with 40% efficiency

As a generator, the faster it spins, the higher the output voltage. so
bigger fan blades would be the easiest starting point.


Typical L.E.D. ratings are:
Color Max. Current Min. Voltage Max voltage
red 30 mA 1.7 V 2.1 V
yellow 30 mA 2.1 V 2.5 V
green 25 mA 2.2 V 2.5 V


So we know the motor isn't going to produce enough current to damage the
LED, we just need to drop the voltage. Try a 10K Ohm pot (linear taper)
in series with the LED and adjust as needed.

 

[mc]

Instead of lighting an LED (since LEDs are ubiquitous and one more LED

in the room at the fair will probably be a big shrug), consider going
with a couple of analog meters to show output voltage and current.
Much more visual appeal; things MOVE!

Also, no specific minimum voltage is needed. You can get meters that
respond to very tiny voltages and currents. LEDs don't light until you get
to 1.8 volts.

 

[Dorian McIntire]

So..i thought..why not run the motor to a set of rechargeable AA
batteries then to a switch...and then to some little led lights. It
is the same idea as far as generating electricity..except it is being
stored for later use.

But then i thought..if i wire the motor right to the batteries....who
is to say the batteries wont keep powering the motor.

So basically...what i need help with is how to wire this...and what
else do i need besides what i have which is:

You really have two choices to simplify the project and keep it from turning
into a Rube Goldberg machine.



1) Use a high torque, low rpm motor. An 18000 rpm motor will never give you
enough voltage at a low rpm. Most rare-earth magnet motors will provide
ample voltage at low rpms.



Many pancake style stepper motors, used in older hard drives, will drive a
LED at low rpms and have multiple phases which helps create constant power
throughout a 3 or 4 phase cycle. I've seen people create artistic windmills
out of these motors which produce a wonderful light pattern on the windmill
using LEDs when the wind blows.



2) Use a gear drive or belt drive to take the relatively low rpms of the
propeller to match the requirements of the higher rpm motor. This is how
most working wind generators work.

I didn't see the second identical thread so I posted this twice.

Dorian

 

[DJ Delorie]

Instead of lighting an LED (since LEDs are ubiquitous and one more LED
in the room at the fair will probably be a big shrug), consider going
with a couple of analog meters to show output voltage and current.

I used the same trick when building a rocket launch controller. With
igniters, you want to pass the tiniest measurable current through them
to test connectivity, but not enough current to actually ignite them.
Most people use small incandescent bulbs. Some use low current LEDs
(~ 5mA). I used a 50 uA panel meter. Much safer, and easier to read
in direct sunlight too.