Product specifications

Instrumentation Laboratory Exercise 28
3.4 Test procedure
Set the power supply voltage to 2 V, and allow the motor to spin up
to its maximum speed. Notice what happens to the numbers as you
apply a load to the motor. Using a piece of paper slowly apply
pressure to the motors disk until the motor stalls. Record the no- load
voltage, current, and resistance. Record these parameters for the
stalled case as well. Repeat this for 3 V and 4 V power supply
voltages. Record your results on the Test Report sheet. Save a few
seconds of data to a file and plot it in Microsoft
®
Office Excel. Verify
that it looks the same as what you saw on the screen.
You will notice that as the load on the motor is increased, the current
draw is increased. The torque of a permanent magnet DC motor is
directly proportional to the torque. Also you may note that the power
supply voltage drops some what as the current increases. This "droop"
varies with power supply design. Better quality power supplies have
less droop. Some of this voltage reduction is also caused by greater
voltage losses in the wires due to higher currents. For a given
resistance of wire doubling the current will double the voltage drop
across the wire, because V = I × R even for wires.