Build a transformer
PARTS AND MATERIALS
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Steel flatbar, 4 pieces
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Miscellaneous bolts, nuts, washers
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28 gauge "magnet" wire
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Low-voltage AC power supply
"Magnet wire" is small-gauge wire insulated
with a thin enamel coating. It is intended to be used to
make electromagnets, because many "turns" of wire may be
wrapped in a relatively small-diameter coil. Any gauge of
wire will work, but 28 gauge is recommended so as to make a
coil with as many turns as possible in a small diameter.
CROSS-REFERENCES
Lessons In Electric Circuits, Volume
2, chapter 9: "Transformers"
LEARNING OBJECTIVES
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Effects of electromagnetism.
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Effects of electromagnetic induction.
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Effects of magnetic coupling on voltage
regulation.
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Effects of winding turns on "step" ratio.
SCHEMATIC DIAGRAM
ILLUSTRATION
INSTRUCTIONS
Wrap two, equal-length bars of steel with a
thin layer of electrically-insulating tape. Wrap several
hundred turns of magnet wire around these two bars. You may
make these windings with an equal or unequal number of
turns, depending on whether or not you want the transformer
to be able to "step" voltage up or down. I recommend equal
turns to begin with, then experiment later with coils of
unequal turn count.
Join those bars together in a rectangle with
two other, shorter, bars of steel. Use bolts to secure the
bars together (it is recommended that you drill bolt holes
through the bars before you wrap wire around them).
Check for shorted windings (ohmmeter reading
between wire ends and steel bar) after you're finished
wrapping the windings. There should be no continuity
(infinite resistance) between the winding and the steel bar.
Check for continuity between winding ends to ensure that the
wire isn't broken open somewhere within the coil. If either
resistance measurements indicate a problem, the winding must
be re-made.
Power your transformer with the low-voltage
output of the "power supply" described at the beginning of
this chapter. Do not power your transformer directly
from wall-socket voltage (120 volts), as your home-made
windings really aren't rated for any significant voltage!
Measure the output voltage (secondary
winding) of your transformer with an AC voltmeter. Connect a
load of some kind (light bulbs are good!) to the secondary
winding and re-measure voltage. Note the degree of voltage
"sag" at the secondary winding as load current is increased.
Loosen or remove the connecting bolts from
one of the short bar pieces, thus increasing the
reluctance (analogous to resistance) of the
magnetic "circuit" coupling the two windings together. Note
the effect on output voltage and voltage "sag" under load.
If you've made your transformer with
unequal-turn windings. try it in step-up versus step-down
mode, powering different AC loads.
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