BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL
Page
6
November 2002
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ARMATURE CURRENT
Figure 2
SPEED
TORQUE
In the separately excited motor, the motor is operated as a fixed field shunt motor in the normal running range. However, when
additional torque is required, for example, to climb non-level terrain, such as ramps and the like, the field current is increased to
provide the higher level of torque. In most cases, the armature to field ampere turn ratio can be very similar to that of a
comparable size series motor (Figure 3.)
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Figure 3
SPEED
TORQUE
Aside from the constant horsepower characteristics described above, there are many other features that provide increased
performance and lower cost. The following description provides a brief introduction to examples of some of these features.
Section 1. 2 Solid-State Reversing
The direction of armature rotation on a shunt motor is determined by the direction in which current flows through the field
windings. Because of the of the shunt motor field only typically requires about 10% of the armature current at full torque, it is
normally cost effective to replace the double-pole, double-throw reversing contactor with a low power transistor H-Bridge
circuit (Figure 4).
