Project 35
3-Speed Motor - Voltage
This circuit is just like the preceding one, except the meter measures the voltage instead of
the current. Build the circuit, set the switcher (S6) to the middle position (off), set the meter
(M5) to the 5V setting, and leave the fan off the motor (M1). Push switch (S2); the motor
spins, and the meter measures the voltage. Turn on the slide switch (S1) or set the switcher
to the right position to adjust the motor speed. You may need to give the motor a push to
get it started, but do not touch it while it is spinning. Sometimes the lamps may not light.
Now place the fan on the motor and try the different switch combinations again.
Turning on the other lamps diverts
current away from the motor, re-
ducing the voltage across it and
slowing it down.
Compare the voltage measurements with out the fan to those with the fan.
!
WARNING:
Moving parts. Do not
touch the fan during operation.
!
WARNING:
Do not lean over the motor.
5V
+
Project 36
3-Speed Motor with Fan
Build the circuit, set the switcher (S6) to the middle position (off), set the meter
(M5) to the 1A setting, and place the fan on the motor (M1). Push switch (S2);
the motor spins, and the meter measures the current. Turn on the slide switch
(S1) or set the switcher to the right position to adjust the motor speed. You may
need to give the motor a push to get it started, but do not touch it while it is spin-
ning. Sometimes the lamps may not light.
Turn on the slide switch and set the switcher to the right (so both
switches are on), and push the press switch to get the fan spin-
ning fast. Now turn off the slide switch and watch how long it
takes to light the middle lamp; how long does it take to light, and
why?
!
WARNING:
Moving parts. Do not
touch the fan during operation.
!
WARNING:
Do not lean over the motor.
+
1A
-40-
SC_STEM1_manual_PRINT.qxp_Layout 1 7/13/17 4:43 PM Page 41
