help with kids science project

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!!!!

Ron

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!!!!

Ron

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!!!!

Ron

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.

is one convenient source of analog meters; drill down in their menus though the tools & test equipment menu into the "other meters" category.

--
Rich Webb   Norfolk, VA

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.

Have you used a voltmeter to determine what voltage you are getting out of the generator? It has to be higher than the battery voltage, or the battery won't charge. Also, the diode (I suggest a 1N4001) will cost you an additional 0.7 volt. That is, if the battery is charged to 1.4 volts and is charging through a diode, the generator will have to output 2.1 volts.

Voltage is like pressure -- it determines which direction the current flows in. (Like water flowing from the higher to the lower pressure in a system.) Current (amperage) indicates number of electrons per second (the number of electrons per second in one amp is gigantic).

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.

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.

Dorian

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

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.

Ron, Before I try to steer you away from your project, I would like to say that it is an excellent idea for a project...but not really a beginner project. The problem is that unless you are using very large blades, it is very difficult to get wind to produce electricity. But, a simpler project which will demonstrate similar principles is to build a hydro-generator. So, instead of using a windmill, you can make a watermill. I jugded a science fair last year where a kid used an aquarium, an aquarium pump, a small DC motor, and a set of Tinker Toys. The aquarium served as the pump reservior; the pump was used to shoot water onto the blades of the water wheel - made by Tinker Toys. He used a DC motor which was wired through an ammeter to a small voltage light bulb (6V I think). He used a voltmeter and the ammeter to determine power output. He changed the angle of the water stream to change the power. If you decide to go with this project, and you need any details, please let me know.

flank