Intro: Build a Coffee Cup Model Wind Charger
Ever wanted to build a wind charger but not sure where to start ? Well now you can enter the world of wind power with this mini model wind charger that produces around 75milli watts of green recycled power. Easily constructed and made of lightweight materials so particularly suited to gusty locations. This little windmill would make a nice addition to a set of solar lights, boosting their power on overcast/rainy days, simply connect the output to the batteries in the solar light.
Heres what you need:
10 X Paper Coffee cups
An old CD
Small scrap of plywood anything above 6mm thickness will do.
A stepper motor from an old printer/fax/scanner/till etc (the older the machine the better usually)
8 X 1N4001 General purpose diodes.
General purpose glue, must adhere to metal.
Miscellaneous small wires
Battery holder to suit batteries
Electrical insulation tape
Note - Not all stepper motors will work well here you must experiment!
Multimeter or ammeter (optional)
Anemometer handy too but not at all necessary.
The video below shows the mini windmill producing some power, the full scale of the meter is 50ma so it's producing around 10 - 30ma typically at wind speed of around 6 - 13mph. It doesn't start charging until around 8.5mph. You can lower the cut-in speed (wind speed that it starts charging at) by just using one ni-cad (1.2v instead of 2.4v). The cut in speed also depends on the amount of cogging your stepper motor has.
There isn't much wind in my garden being surrounded by garden fences, houses and the like, you will get much better performance if you raise the turbine up above everything, but it isn't really worth building such a tall tower for such a small turbine.
Step 1: Mark the Cups Mounting Point
The cups are fitted onto the CD by cutting a slot into the sides of the cups. You need to cut a slot about 2" long at the half way point. To make all of the slots the same size, I used a piece of paper cut to size to mark them out. When you have cut the slots test them to make sure they all slide onto the CD.
Step 2: Cut the "sails" Shape From the Cups
Next you need to cut the front off the cups so that they can catch the wind and make us some power.
You need to remove the front section of the cup as shown in the photos but leave the rim around the top of the cup.
Step 3: Make the Sail Extensions
With the rotor one cup high it doesn't have enough area to turn the stepper motor at a reasonable wind speed so you need to make the cups a little taller. Take three cups cut them in half and cut the rim off the top. Then cut small bevels in the corners where the rim was to help them fit in better
Step 4: Cut the Mounting Slots for the Extensions.
Cut a slot parallel to the front of the bottom sails that is wide enough for the sail extensions. Test fit the extensions in place. The extensions are pushed down about 10mm, they should be reasonably tight.
Step 5: Cut the Adapter for the Stepper Motor
Now we need a way to connect the CD to the stepper motor. Cut a circle that is smaller than the base of the cups. I used 12mm plywood because I had some scraps lying around - you can use anything from about 6mm upwards.
You'll need to drill out the centre of the circle to match whatever cog or shaft your stepper motor has.
The adapter should be a tight fit but not so tight you need a hammer to fit it!
It doesn't have to be a circle though you could use a square piece of timber.
Step 6: Drill and Mount the CD.
Drill two holes either side of the CD then use these to drill pilot holes into the adapter. Then you can screw the CD down with pan head screws.
Step 7: Solder the Circuit Together
Stepper motors output an A.C voltage which is of little use for our battery charging application. So you need to build a rectifier to turn the A.C into DC.
Follow the diagram and solder all of the diodes together as well as the stepper motor and battery pack. I used a three AAA cell holder purely because I had it to hand you only need a two cell holder.
Identifying the motor output wires:
To identify the wires from the stepper motor you can use an ohmmeter to measure the resistance between the wire, the two wires that connect to a coil will have a resistance somewhere between 5 - 100 ohms (roughly). If you don't have an ohmmeter you can simply use an led, connect it to different wires until you find the ones that are producing power. When you have identified the coil pairs, twist them together so you don't lose them.
Ammeter Connection :
I left a break in the wires so I can measure the current flowing to the batteries easily you can omit this if you don't want to measure the output.
If you have connected a meter to the circuit you can spin the motor by hand and see how much current it pushes. I measured around 75ma spinning it by hand.
Make sure that you get all of the lines in the right places on the diodes, they indicate the polarity of the diode and must point the right way. As an alternative to soldering the diodes together you could buy ready fabricated bridge rectifiers (they are very cheap) and connect it all together with screw blocks.
There's no reason why you can't connect some LED's in place of the batteries to make a decorative LED wind spinner., if thats what you'd prefer.
Note: I changed the rectifiers to parallel on 26/04/2010 thanks ghurd and trialex
Rectifying other types of stepper motor:
There are 5 wire and 6wire stepper motors too, The Back Shed has some circuits for rectifying these see here : http://www.thebackshed.com/windmill/assemblyMini3.asp
Step 8: Attatch the Rectifiers to the Motor
I taped the rectifiers to the motor to keep them out of the way and to stop them shorting to the batteries.
First of all put a layer of tape on the back of the stepper motor then thread a piece of tape through the centre of the rectifiers to tape them down. Then tape over it all (gently!)
Step 9: Glue Everything Together
Now you can glue everything together. Glue the cups to the CD and glue the sail extensions to the lower cups
Step 10: Glue the Motor in Place
You'll need to cut a hole to suit your motor in the bottom of a cup, then glue it in place using the adhesive. You can also tape the wires in place underneath.
Step 11: Make Some Tent Pegs
I made some little pegs to hold the generator to the ground out of some copper wire. Simply bend a hook in the end and pierce them through the base cup. You can also use these to pierce two small holes for your meter wire if you intend to use those. If you intend to mount the wind mill on a pole, you can skip this step.
Step 12: Test It
It should be finished now and ready to be tested. You can typically expect there to be absolutely no wind for at least three days after you finish any wind mill, so be patient!
If you're using the tent pegs to hold your turbine down, can simply push them into the ground so that they hook into the holes you made in the side of the cups.
If you're mounting the turbine on a pole you'll need to fix the cup at both sides with two screws either side to prevent the cup from tipping, you'll also need to glue the battery holder to the inside of the base cup (unless you don't mind it hanging loose)
If you have an anemometer you can plot the windmills output versus the wind speed to get an idea of how it might perform in different locations
How much power you get depends on the stepper motor you chose and the wind speed. There isn't much wind in my garden being surrounded by garden fences, houses and the like, you will get much better performance if you raise the turbine up above everything, but it isn't really worth building such a tall tower for such a small turbine.