Elenco Electronics 202 - Manual (Page 22)

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Project #13
OBJECTIVE: To show how switches can increase or decrease
the speed of an electric fan.
Build the circuit shown on the left by placing all the parts with a black
1 next to them on the board first. Then, assemble parts marked with
a 2. Finally, add the 2-snap wires that are marked for level 3.
When you turn on the slide switch (S1), current flows from the
batteries (B1) through the slide switch, motor (M1), the lamp (L2), and
back to the battery. When the press switch (S2) is pressed, the lamp
is shorted and motor speed increases.
The principle of removing resistance to increase motor speeds is only
one way of changing the speed of the motor. Commercial fans do not
use this method because it would produce heat in the resistor and fans
are used to cool circuits by moving air over them. Commercial fans
change the amount of voltage that is applied to the motor using a
transformer or other electronic device.
Two-Speed Fan
OBJECTIVE: To show how a fuse is used to break all current
paths back to the voltage source.
Use the circuit built in project #13.
When you turn on the slide switch (S1), current flows from the
batteries (B1) through the slide switch, the lamp (L2), motor (M1), and
back to the battery. Pretend the 2-snap wire marked fuse in the
drawing on the left is a device that will open the circuit if too much
current is taken from the battery. When press switch (S2) is pressed,
the lamp is shorted and motor speed increases due to an increase in
current to the motor. While still holding the press switch down, remove
the 2-snap wire marked fuse and notice how everything stops. Until
the fuse is replaced, the open circuit path protects the electronic parts.
If fuses did not exist, many parts could get hot and even start fires.
Replace the 2-snap wire and the circuit should return to normal.
Many electronic products in your home have a fuse that will open when
too much current is drawn. Can you name some?
The Fuse Project #14
!
WARNING: Moving
parts. Do not touch
the fan or motor during
operation.
!
WARNING: Moving
parts. Do not touch
the fan or motor during
operation.