A mini-wind generator?

I'm a high school physics teacher and I would like to design a project where students make a mini-windmill generator from a small hobby motor. I would like this mini generator to be able to charge a AA battery that could then be used to light a single light bulb. Is this possible? Would I be able to create a large enough voltage from a small hobby motor to charge a AA battery over time?

A little DC electric motor can charge a rechargeable AA battery cell if the propeller is big enough and if there is enough wind for long enough.
But a light bulb makes mostly a lot of heat and only a little light. Use an LED instead.
A rechargeable battery cell produces only 1.2V. Have you ever seen a 1.2V lightbulb?

You are a teacher who knows nothing about electricity.

audioguru said:

A little DC electric motor can charge a rechargeable AA battery cell if the propeller is big enough and if there is enough wind for long enough.
But a light bulb makes mostly a lot of heat and only a little light. Use an LED instead.
A rechargeable battery cell produces only 1.2V. Have you ever seen a 1.2V lightbulb?

You are a teacher who knows nothing about electricity.

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I think you're being a little harsh on the OP.

Besides which, I've seen light bulbs down around that size; I used to have (as a kid) old Stomper cars that ran off a 1.5 VDC AA cell; in addition to powering the small motor, the cell also powered a small light bulb for the "headlights"...

Grain-of-wheat bulbs is what they were called (and they were available for a variety of voltages).

You might be able to buy 12V "grain-of-wheat" lightbulbs today. But nothing will be only 1.2V. Old Christmas tree lights and penlights were 2.5V.
How about using a voltage stepup circuit like a Joule Thief or the circuit in solar garden lights?
Then the teacher can learn about then teach about those circuits.

1.5 volt GOW lamps are still available in the hobby shops.

Yep. Small 1.5v bulbs are extremely common and used in little flashlights and are very common in cheap educational "learn electronics" kits that teachers often buy from the electronics and toy shops. I'm guessing you don't buy "learn electronics" kits much these days Audioguru?

Sstambach- You could use those little stepper motors you can get for free from any old fax machine or bubblejet printer, if you connect one winding to a 1.5v bulb it will light up from very low RPMs, unlike most cheap little DC motors thast will need to turn very fast to generate any significant power.

How dim will a 1.5V incandescent heater (old fashioned lightbulb) be with only 1.2V from a rechargeable battery cell?
How dim will it look when the battery voltage drops to 1V or less?
Why don't you use efficient LEDs powered from 6V?

audioguru said:

How dim will a 1.5V incandescent heater (old fashioned lightbulb) be with only 1.2V from a rechargeable battery cell?
How dim will it look when the battery voltage drops to 1V or less?
Why don't you use efficient LEDs powered from 6V?

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One reason I can think of why using an incandescent lamp over an LED, for the purposes of demonstration and teaching - would be that it is fairly easy to show a relationship between wind speed, voltage, and amount of power generated, by the brightness of the bulb. Plus (if the bulb is a large enough load), you can feel the resistance (or show the resistance) of the load to the generation capability when switching the load in and out (by speed of the generator being affected).

I'm not sure this would be as apparent with an LED, simply because at a certain level, the LED is just "on" or "off" - not much in-between, plus because it doesn't take much current to light an LED, you couldn't as easily demonstrate the current/resistance, etc.

Finally - I would say allow for both, to show the efficiency of LEDs over incandescent bulbs - how many LEDs can be lit vs bulbs and experiments of that nature (teach the science: have a hypothesis, set up the experiment, test the results, find the conclusion). There's a whole lot of interesting ways this kind of demonstration and experiment can be shown to kids to really teach them a lot (assuming it is handled properly, and not ham-fisted and spoon-fed to them - also with the hope they are interested - hard to say nowadays).

An incandescent light bulb is a heater. Its filament gets to 2000 degrees or more and wastes most of the current making heat and making only a little amount of light.
An LED makes plenty of light and about the same amount of heat. But the wasted heat is much less than an incandescent light bulb.

A light bulb shines all around. An LED is focussed into a fairly narrow beam in one direction.

audioguru said:

An incandescent light bulb is a heater. Its filament gets to 2000 degrees or more and wastes most of the current making heat and making only a little amount of light.
An LED makes plenty of light and about the same amount of heat. But the wasted heat is much less than an incandescent light bulb.

A light bulb shines all around. An LED is focussed into a fairly narrow beam in one direction.

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Not sure what your point is (everything you said above is true; no argument there - just that this is fairly well understood); my point is that an incandescent bulb provides to kids an immediately visible means of showing speed (of wind generator) to voltage/power to light - that the faster the generator turns, the more light you get (and conversely, the slower it turns, the less light). Its a physical manifestation that is easy to understand.

Whereas an LED, once you get past the forward voltage, you can't really see much in the way of speed showing output; the LED is either on or off, very little in-between except for change in current.

I'm not arguing that one or the other is better (certainly, LEDs are better efficiency-wise) - just that an incandescent bulb provides a more easily grasped (by kids) example of power generation. That doesn't mean that LEDs can't be incorporated as well; in fact they should be, but presented in a manner so that the kids can understand how and why they are better (as well as their downsides - such as you mention about dispersion of light - and perhaps let the kids brainstorm how to make up for that shortcoming?)...

Last year i spent time helping a young girl in the States with a science fair challenge of all the states of USA, to design a efficient wind generator blade.

The challenge had rules that they had to work within.
Some of these rules were, a blade set no larger in diameter than 1 foot, the motor used was from a CD player, and the blade set needed to incorporate the centre of a CD as the hole was used for mounting the blades to the test generator.
The voltage produced was recorded and not used to charge a battery but that could have easily been done.

Small toy Dc motors work very well for this and can be better than stepper motors.
Stepper motors have a "cogging effect" that takes a lot of wind energy to over come to get the blades to start, DC motors dont suffer from this problem.
Steppers generate AC power and need to be rectified, where DC motors dont.

All said a stepper motor will produce more power and likely at a lower rpm.

The method of displaying the power generated is irrelevant, as the quest is to produce the power in the first place.

Should the OP like to take this to a higher level and record the power (voltage) generated onto a laptop computer i am able to help achieve this.

The rule of thumb with DC motors used as wind generators is, to take the rpm of a motor at its rated voltage, divide the rpm by the rated voltage, then times the result by the voltage you require from the generator to charge your battery, this will give you the rpm the motor will need to spin at to reach cut-in voltage to start charging the battery.
As the mill spins faster from this rpm the current (amps) to the battery will increase.

Ie:- 12 volt motor rated at 1000 rpm

1000 / 12 = 83.33

83.33 X 1.4 = 166.66 rpm needed before current will start to flow to the battery.

There is a lot to build in a mini mill and as much to be learn from doing it.
It is not a 5 minute job and can be very rewarding or frustrating.

You also need some form of a charge controller to prevent the battery from being over charged, as a mill will keep increasing its voltage with higher rpm, and with wind you dont have a lot of control over this.

Pete.

Audioguru-

How dim will a 1.5V incandescent heater (old fashioned lightbulb) be with only 1.2V from a rechargeable battery cell?
How dim will it look when the battery voltage drops to 1V or less?

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I have a couple of tiny Eveready plastic waterproof flashlights that use a single AA cell. They are very bright right down to about 1v and are fantastic for motorcycle toolkits.

Yes agreed with crosh..nothing beats a little incandescent bulb in this demonstration simply because it can show more accurate view of the amount of power generated/stored etc. AG, can't you feel that?

A kid on this forum asked why the little computer fan (used as a generator) on his bicycle didn't light his array of LEDs. It was a windmill wasn't it?
We explained that it was too small so produced a very low current and it didn't spin fast enough so its voltage was low.
He didn't understand that the power produced by the windmill comes from how hard he is pedalling. If the fan had huge blades and spinned very fast then the LEDs would be bright but he would get tired pedalling. Like pulling an open umbrella behind him.

Your windmill might need gears or a pulley to spin the generator fast enough to light a little incandescent light bulb.

AG,

I understand your point on gearing, but would say its bad advice.
Once you go away from 1:1 ratio you lose efficiency fast.
It might be a good science experiment to show the effect of efficiency over gearing but you will never extract the same amount of power as a suitable generator using a 1:1 ratio.

Better to find a generator more suited to the rpm range, than to try to adapt the rpm to suit the generator.

First rule in wind energy is 1:1 ratio is best.
Even the big commercial mills are starting to design away from gearing due to the losses incurred.

The OP might like to have at look at this link for use of a stepper motor and ideas of assembling a mini mill.

https://www.thebackshed.com/Windmill/assemblyMini1.asp

Pete.

The Backshed windmill has a pretty big propeller that spins at a fairly high RPM. I think it is too dangerous for little school kids.
I was thinking of a propeller with a lot of blade area that spins slowly, then gears or a pulley system to spin the motor at a high speed.

My RC electric model airplanes have gears so that the tiny motor spins fast and the propeller has lots of torque.

AG,

Sorry mate, i have been around wind energy too long and will say gearing wont work.
Extracting energy from the wind is a fine art, and once you step outside of the square of efficiency losses add up real quick.

The big blade set shown is partly due for the need to overcome the cogging effect of the stepper motor to get it to startup.

As a mill will need to be in clean non turbulent air it would be out of reach of small kiddies anyhow and the wires can be run down to the ground where the kids can fiddle with them........So all safe

The more blades you have the higher the torque but the lower the rpm, even a toy motor will require a blade set of around 1' dia. to extract energy.

I am currently in the process of constructing a 1-3Kw wind turbine and i also need to follow the same rules as is needed to construct a mini mill, if gearing and small blade sets worked we would all be using them, and the simple fact we dont should imply a reason.
It has all be tried and failed, this is why i say its not worth doing what has been well tested before.
Bryan1 on the forum here lives off grid and relies on wind energy, and has as much experiance with turbines as myself, and will also tell you how fickle they can be to get good results of energy extracted from the wind.

Pete.

Back on Topic

Hello Sstambach,
That link SABorn did in post #15 would be your best bet as that article on the backshed does cover it very well from start to finish. Now the only thing I would ask if you are going to use that backshed article to contact Gizmo who owns that website and I'm sure he will happily give you the go-ahead to use it. ( Either SABorn or I can help you with that )

Using a small stepper motor and making some PVC blades would be the easiest way to demonstrate a mini mill and it is definitely the teachers job to make it, get it on a tower much higher so the fast spinning blades CANNOT be touched by any student.

If you need any assistant just say so and myself and others will help out on your school project.

Regards Bryan

audioguru said:

You might be able to buy 12V "grain-of-wheat" lightbulbs today. But nothing will be only 1.2V. Old Christmas tree lights and penlights were 2.5V.
How about using a voltage stepup circuit like a Joule Thief or the circuit in solar garden lights?
Then the teacher can learn about then teach about those circuits.

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Error!

There are 1.2V/150mA light bulbs with E-10 socket on the market. Next type is 1.5V/200mA

Boncuk said:

Error!

There are 1.2V/150mA light bulbs with E-10 socket on the market. Next type is 1.5V/200mA

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About 35 years ago I bought 12V grain-of-wheat light bulbs for my car. They were tiny, the size of a grain of wheat or rice and had wire leads, not a socket. I think they were 40mA.
All the ones shown for sale in Google are 12V-16V, not 1.2V. Hobby stores sell them for model trains amd doll houses.