Specifications

Regulation I Current Limit I Efficiency
Motors can handle currents in excess of their rated values for
short periods of time. However, if operation outside of rated
values occurs for an excessive duration of time, armature and
brush life reduce, and eventually permanent motor damage will
occur. Minarik drives generally possess a current limit (or
torque limit) trimpot adjustment that allows users to limit the
amount of current drawn by a motor. Consequently, users can
limit the torque delivered to the load from a motor.
NOTE: THIS ADJUSTMENT IS DESIGNED TO LIMIT STEADY STATE OVERLOADS AND MAY
NOT LIMIT VERY FAST CHANGING (IMPULSE) TYPE LOADS.
Efficiency is usually described as
hh
= (power output ÷ power
input) x 100% .
System efficiency corresponds inversely with power consump-
tion from the power company. Higher system efficiencies
consume less electricity than lower system efficiencies. They
also correspond, though not linearly, with system life. Primarily,
we are concerned with the efficiencies of the motor, drive and
system.
When a device cannot convert all of the input power into work,
the excess energy is wasted as heat and sometimes, noise.
Usually, one must know the efficiency of the motor and drive
only for a calculation of heat dissipation; for example, when
sizing an enclosure for a drive. Another example might be the
sizing of a cooling fan for a non-ventilated motor. The greatest
contributing factor to motor and system efficiency is form fac-
tor. The graph below describes typical system efficiencies using
Minarik drives.
We define the regulation speed of a DC brush-type motor
as the drive
‘ s ability to hold a desired set speed as the
load seen by the motor changes. We illustrate this below
using the speed/torque curve of a DC motor controlled by
DC drives. The horizontal line represents “perfect speed
regulation” for a given motor. The motor speed does not
change, not even 1 RPM, even though the motor experi-
ences an increasingly heavier load.
Once the motor sees a load in excess of its rating, the
drive may go into “current limit” to protect the motor. Until
then, we want the drive to regulate speed. The amount of
regulation required depends on the application; users set
its value by calibrating the IR COMP trimpot on the drive.
Drives can regulate motor speed even more accurately
when they employ external feedback devices to monitor
motor speed.
Applications requiring tight regulation might be:
a) Cut-to-length
b) Leader-follower (involving multiple axes)
c) Winding applications
d) Printing, marking, labeling, and gluing
(requires a high level of accuracy)
Applications where precise speed regulation may not be
as critical:
a) High-speed braking and reversing
applications (like index tables, palletizers,
strapping, cranes, hoists, lifts)
b) Applications where simply moving from point
A to point B is sufficient
c) Applications where an operator uses visual
feedback (eyeballs) to make speed adjustments
Reference
REGULATION
CURRENT LIMIT
EFFICIENCY
0 31
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REFERENCE