Transcript SECME-Generator-Building-Presentation-11-22-13

SECME
Generator Building
Competition
TOPICS
• Purpose & Necessity
• Competition Rules & Scoring
• Basic Theory of Electrical Generators
• Generator Building Instructions
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PURPOSE
&
NECESSITY
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Purpose & Necessity
The generator building competition will prepare the
students for the FCAT and other STEM programs by
challenging them to understand the following:
• Basic forms of energy, including electrical, mechanical, and
conversions from one form to another.
• The basic magnetic theory
• The relationship between magnetic and electric fields.
• The flow of electrical circuits.
• The law of electromagnetic induction (Faraday’s Law).
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COMPETITION
RULES
&
SCORING
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Competition Rules
Team Entry:
• Minimum of 2 and a maximum of 4 team members. One team
per school.
Design:
• Construct a generator and measure the voltage output
• The voltage must be generated using electromagnetic induction
(no static electricity, photovoltaic, etc)
• The design should produce a continuous voltage, not a single
spike.
Communication:
• Team will be interviewed by judges (written and oral)
• Team shall provide a drawings with a one page abstract
• Technical Report (Future Competitions)
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Competition Scoring
Generator Output: (Voltage output x 200)
• The highest voltage achieved in a 30 second duration will be
recorded towards final score.
Team Interview: Max 100 points
• Application of technical principles (40pts) – Written test
•
Knowledge of design (20pts)
•
Demonstrate knowledge of Ohms Law (20pts)
•
Creativity (20pts)
Design Drawing plus 1 page abstract: Max 100 points
Awards will be 1st, 2nd and 3rd place winners.
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Generator Requirements and
Guidelines
• Maximum Dimensions: 30 cm X 30 cm X 30 cm
• No batteries, or external voltage source can be used.
• No generator kits allowed
• All items must be hand assembled
• Generator must be able to run for continuously for 30sec.
• Materials such as wood, cardboard, plastic, etc. can be used for
the base of the generator. Long nails, screws, pencils, etc. can be
used for the rotor.
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Material List
500' Maximum of #28AWG Magnetic Wire
•
Approximate cost: $10.00
http://www.amazon.com/Magnet-Plain-Enamel-NylonInsulated/dp/B00B887G6Y/ref=sr_1_10?s=industrial&ie=UTF8&qid=1382704057&sr=1-10&keywords=28+awg+magnet+wire
Magnets:
• Elementary and Middle school must use option (a)
• High school may choose either (a) or (b)
• These are strong magnets. Handle carefully to avoid pinching. They may
lose their magnetism if chipped or damaged.
• Keep magnets away from sensitive electronics and credit cards.
(a) Maximum 4: Ceramic Bar Magnets (3/8” x 7/8 x 1-7/8”)
Cost: $5.34 http://www.homedepot.com/s/ceramic%2520block%2520magnets?NCNI-5
(b) Maximum 12: Ceramic Disk Magnets (3/16” x 1/4”)
Cost: $5.64 http://www.kjmagnetics.com/proddetail.asp?prod=D34-N52&cat=168
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Elementary School: Rules & Scoring
Safety precautions must used when constructing and testing the
generator. Safety glasses, gloves, etc. must be worn.
• Rotor will be turned by a standard electric drill at a set speed of
approximately 200 rpm.
• Judging will be based on the maximum peak voltage output for
a duration of 10 seconds.
• The rotor is to stick out at least 2cm for the judges to attach the
electric drill.
• The students must have an adult help them with the drill
portion; when testing their design.
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Middle School: Rules & Scoring
Safety precautions must used when constructing and testing the
generator. Safety glasses, gloves, etc. must be worn.
•
The students are to construct a generator powered by wind.
•
Wind source used shall be from a shop/home vacuum.
•
Students will operate the vacuum themselves.
•
Judging will be based upon maximum peak voltage output for
a duration of 30 seconds.
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High School: Rules & Scoring
Safety precautions must used when constructing and testing the
generator. Safety glasses, gloves, etc. must be worn.
•
The students are to construct a generator powered by water.
•
Water source used shall be from from a 1 gallon container & a
funnel with a flow rate of 2 gal/min
•
Students to place the funnel apparatus and pour the water
themselves.
•
Judging will be based upon maximum peak voltage output for
a duration of 30 seconds.
•
Water shall not come in contact with the generator structure.
Students shall build a sheilding device to prevent water from
contacting the generator structure.
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BASIC THEORY
of
ELECTRICAL
GENERATORS
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Basic Theory
How does a Generator Work?
• It’s a machine designed to convert Mechanical Energy
to Electrical Energy.
• Based on the principle of electromagnetic induction,
which was introduced by Michael Faraday in 1831.
Three things are required to build a generator:
• A magnetic field
• Current carrying conductor
• Relative motion between the two.
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Basic Theory
Magnets
Material or object that produces a magnetic field.
• Permanent
• Temporary
Magnets have a south pole and a north pole
• Like poles repel each other
• Opposite poles attract each other
• Magnetic fields are strongest near the poles
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Basic Theory
Magnets
Magnets can be magnetized through length or
thickness.
Magnetized through
thickness
Magnetized through length
A compass or another magnet can be used to
determine the axis of magnetization.
The magnets that were provided by Broward SECME
coordinators are magnetized through their thickness.
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Basic Theory
Faraday’s Law- Electromagnetic Induction
200 years ago Michael Faraday proved that a magnetic field could
induce an electric current using this experiment:
Lenz’s law: the induced magnetic field acts to oppose the motion of the
changing magnetic field.
E.g. 1: The induced field creates a S pole to repel an approaching S pole.
E.g. 2: The induced field creates a N pole to attract the retreating S pole.
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Basic Theory Overview
Faraday’s Law- Electromagnetic Induction
Faraday’s Law:
d
V  N
  N sin 
dt
N = # of coils of wire
ω = Speed of rotation
Ф = Magnetic flux
Q = Angle between
magnetic flux & conductor
How do we maximize voltage (V) output?
• Increase the # of coils (N)
• Increase the speed of rotation (ω)
• Decrease friction
• Lighter magnets
• Better wind/hydro fan blades
• Increase the Magnetic Flux (Φ)
• Use stronger magnets
• Ensure that magnets are as close to the wire as possible
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GENERATOR
BUILDING
INSTRUCTIONS
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Generators – How they work
• The rotating parts of a generator are called the rotor. Can
be a nail, screw, or metal rod.
• Basic generators use strong permanent magnets mounted
on the rotor. Magnets always have a pair of poles (N & S).
More than one pair of poles can be used.
• The stationary parts of a generator are called the stator. The
stator consists of a tightly wound coil of wire. The stator
windings may vary depending on the number of rotor poles
used.
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Steps to Build Generator
i.
Build the stator from wood, plastic, cardboard, etc. It must be
large enough to wind the wire around and it must be able to
support the rotor. Generator must be ≤ 30cm x 30 cm x 30cm.
ii.
Mount the rotor on the stator. It should be able to turn with little
friction. One end of the rotor should extend out at least 2cm
from rotor so there is space to apply drill/wind/water.
iii.
Mount the magnets on the rotor. The poles must face outwards.
iv.
Wrap a coil of wire around the stator. One side of the coil
should see a “N” pole and the other side should see a “S” pole.
v.
Scrape of the insulation from the ends of the wire with
sandpaper.
vi.
Create rotor blades to capture water/wind. Test it (set voltmeter
to a/c volts)!
These are the basic steps. Feel free to improvise.
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Sample Design 1
The Correct Construction – Single Magnet
Fleming’s Right
Hand Rule
Direction of
Current
Rotor
Applies to current
flowing in straight
conductor
Field, current,
motion in different
dimensions
Example of a rotating Magnet and a stationary coiled wire
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Sample Design 1
What Not to Do!
Poles do not
point
outwards
Magnetic field does not change as shaft
rotates
Violates Fleming’s rule (current
in same dimension as motion)
Wire sees a small magnetic field since N
& S poles cancel each other.
Pay very close attention to the orientation of the magnets
with respect to the coil.
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Using Multiple Poles
2 Poles
Correct!
•Magnetic poles always come
in pairs.
•Increasing the # of poles
increases the rate of change of
magnetic flux, which increases
voltage.
Magnetic Field Strength
1
0.5
0
-40
60
160
260
360
-0.5
-1
Degrees
Correct!
•Poles must alternate between
North & South.
•Use compasses to identify and
label the poles.
Generated
voltage is ~ 0
Magnetic poles must alternate between
North & South.
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Incorrect!
Sample Design 2
What Not to Do!
Remember Fleming's RHR.
Direction of
Current
- Ensure that current will not cancel
itself out.
Opposite sides of the coil see
the same polarity. Current
cancels itself out
The coil must run across a North & South Pole or else the
current will cancel itself out.
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Sample Design 2
The Correct Multiple Pole Construction
When connecting coils
make a connection
between wires across
opposite poles.
Direction of
Current
The coils may be
wired up separately,
tested, and then
connected.
Stator
If connected
incorrectly the currents
will cancel out.
Poles & coils should
be equal distance
apart so that currents
are in phase.
To best utilize a 4 pole generator there should be a coil across
each pair of poles. The coils can be tested individually.
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Sample Design 1
Examples
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Sample Design 2
Examples
•
This design uses a tightly
wound coil instead of straight
conductors.
•
The field can be
strengthened/concentrated
by wrapping the coil around
an iron core.
•
This design is very similar to
Faraday’s experiment.
•
Try different magnet
configurations.
•
Try different coil shapes.
Note: The lines of magnetic flux are strongest at the ends
of the magnets.
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Sample Design 3
Construction
• If a 4 pole rotor is used, ensure that each end of the
coil sees a different polarity
– Otherwise the induced field & current will cancel itself out.
N
N
S
Correct
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N
Incorrect
Generator Building
Rotor Blades
• “Give me a lever long enough and I will move the world” –
Archimedes, 287 BC
– Torque = Force x distance from point of rotation
• Try lots of things. Have fun with it!!
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EXAMPLES
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EXAMPLES
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Demonstration
During Seminars (only)
Build small model generator
• Generates 0.1 - 0.5 Volts
Exercise
• Each group will be given a stator (cardboard),
rotor (screw), magnets and wire (100’)
• Mount magnets on the rotor in the proper
configuration
• Wrap wire around the stator
• Remove insulation from the ends of the wire
• Test the generator
Discussion
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