EECS 314 Winter 2009
HW 08 Extra credit problem on the Inductive Kick
© 2009 Alexander Ganago
Page 1 of 4
Extra Credit Problem on the Inductive Kick
(50 points)
Due date: Tuesday March 24, 2009, before the lecture
An abrupt change of inductor current (for example, an interruption of current when
the switch is suddenly open) causes an abrupt change of inductor voltage, known as
the inductor’s kickback (which can damage the switch and can be dangerous for the
human operator). Note that an inductor has many loops of wire around a magnetic
core, and an electric motor has many loops of wire around a magnetic core thus
motors act as inductive loads, in particular, motors exhibit the kickback.
Consider the circuit shown on the
diagram. Here the battery is shown as a
combination of the voltage source V
B
and resistance R
B
; the DC motor is
shown as a series combination of the
inductance L and resistance R
M
, and R
S
is the shunt resistance.
Consider the role of the shunt resistor R
S
: if it is large, the inductive kick at time t=0+
gets high and dangerous for the operator and the circuit; if R
S
is small, it consumes
too much power at time t<0 (due to current division).
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 Winter '07
 Ganago
 Volt, Inductor, Electrical impedance

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