Physics help: i need to build a generator! (more details added)

[Crappopotamus]

My school is entering into a physics contest...

edit:
here are the specifications:
groups will design and build a wind generator using environmentally friendly parts. the winner will produce the most current. judgin will be based on the max current produced in a 30 sec window using a multimeter with a max reading of 10a. if tied, the winner will be the team with the lightest generator.

the generator will be powered by a fan as a wind source that sits on the floor and measure aprox 55cm squared

So far, our idea is to make a big U shaped metal thing, and coil it with wire. between it, we're going to put a magnet, and its going to spin, and its going to produce current in the wire. We imagine it like an electric motor, but opposite.

One of the problems we forsee is that to produce a lot of current, you have to use a powerful (and heavy) magnet. Thats going to be tough to turn with a fan....
What other problems might we run into? a better approach?

oh yes, and try and keep terminology REALLY SIMPLE CAUSE WE'RE DUMB.

 

[flot]

Don't forget to harness as much of the "wind" as you can.

Unless there are rules against it, it might work to your advantage to make a "funnel" of sorts out of cardboard and duct tape etc - make the mouth as big as the fan outlet, and push it up against then fan - then channel all the air into a smaller housing where your generator is. You'll increase the velocity of the air, which I _think_ will help you out, depending on your design.

 

[K1052]

mini gas powered turbine?

 

[RU482]

10 Amps at what voltage?

 

[PowerEngineer]

Originally posted by: redly1
10 Amps at what voltage?

Good question...

You'd normally rate a generator based on the watts (actually volt-amps) it produces at a given voltage, which equates to a current. If the watts or voltage isn't specified, then you can maximize your current by simply connecting the ends of the stator coil together (0 volts and 0 watts)!

I'm assuming you're building an AC generator. You'll want to wrap and mount the "stator" coils so that their axes are perpendicular to the axis of rotation for the magnet (to maximize the flux change captured by each loop of the winding). The coils should be wrapped around something friendly to magnetic fields (i.e. iron), and the "air gap" between the coils and the spinning magnet should be as small as possible. If you make several (identical) coils instead of just one, then you can connect them in different series and parallel combinations to get different voltage/current results (highest current is all in parallel). Assuming a single rotating magnet (i.e. two poles), you should actually have your stator coils wrapped around two iron cores 180 degress apart (i.e. on opposite sides of the rotor). When connecting these coils, remember that the flux change (and therefore induced volatge) on one side is opposite the other side. If you wanted to rotate two magnets (at 90 degree angles to each other), then you can have four coils 90 degress apart.

You can also consider using an electromagnet instead of a natural magnet for the "rotor". Again loops of wire around an iron core. You should be able to mount a couple (for balance) 9v batteries wired in series to power it. Or you can build some slip rings on the end of the rotating shaft so that you can use a stationary DC voltage source.

Good luck!

 

[Crappopotamus]

clarified, and bump!

 

[Crappopotamus]

bump?

 

[DrPizza]

Crappo, I was considering doing this as a project with my physics class, welding class, and shop class combined (a few years ago, the physics/other classes built a kick ass trebuchet). I came across the idea while searching for magnets for sale. One thing that'll help you is to use STRONG magnets. I'll see if I can find a link to the site that gave me the idea. It was basically hillbilly rednecks meet physics majors meet geeks meets junk yard wars. These guys built their own windmills and water generators from scrap stuff (plus the wire and magnets)

But, if you're being judged soley on the current, and not the voltage... couldn't you incorporate a step-down transformer to decrease the voltage and increase the current?

hunting for link now...

 

[DrPizza]

here! Even a hamster powered generator
Should get some good hints from that site... just spend a while browsing how they built their windmills.

 

[WinkOsmosis]

 

[OrganizedChaos]

if there only measuring current put a step down trransformer in it somewhere. say your generator makes 5 amps at 10 volts, step that down to 50 amps at 1 volt. if theres a 10 amp max there probably using a plain old DMM and not an amp clamp. you'll be sure to win when his meter starts smoking.

/disclaimer am not a EE math could be wrong or something

 

[Crappopotamus]

woooo. thats an awesome site. thanks so much sir.

whats with this transformer dealie? can i build one myself?
heres what i got from encarta...

When an alternating current surges back and forth through a coil of wire, the magnetic field about the coil expands and collapses and then expands in a field of opposite polarity and again collapses. In a transformer, a coil of wire is placed in the magnetic field of the first coil, but not in direct electric connection with it. The movement of the magnetic field induces an alternating current in the second coil. If the second coil has more turns than the first, the voltage induced in the second coil will be larger than the voltage in the first, because the field is acting on a greater number of individual conductors. Conversely, if there are fewer turns in the second coil, the secondary, or induced, voltage will be smaller than the primary voltage.

um okay, well how does it hook into the circuit of the alternator (the hamster cage generator)?

a major problem ive got is how to make this fan/turbine. we've got to make it ourselves... and its going to have to turn the rotor, which should have a lot of powerful (and heavy) magnets. bah. oh and flot, i just saw your post, i already thought of that the fan is 55cm squared... our fan will likely be much smaller (easier to build)

 

[Crappopotamus]

bump. so heres the plan now.

funnel -> fan of some sort... -> hooked to circle of magnets, with alternating polarity -> induces current and voltage in a nearby coil -> coil is in a step down transformer, the measured current is from a very small coil.

 

[arcenite]

buy 1000000 hard drives off ebay and use the magnets out of them

 

[Crappopotamus]

Originally posted by: DrPizza
But, if you're being judged soley on the current, and not the voltage... couldn't you incorporate a step-down transformer to decrease the voltage and increase the current?

is this true? i was talking to a teacher, and he was not sure that decreasing voltage would necessarily increase current. how does a transformer look, and how could we build it?