August 2012
L010440
10
Determine Output Current
The output current used for motor when microstepping is determined differently from that of a
full/half step unipolar driver. In the MBC25SI1TB, a sine/cosine output function is used in rotat-
ing the motor. The output current for a given motor is determined by the motors current rating
and the wiring configuration of the motor. There is a current adjustment potentiometer used to
set the output current of the MBC25SI1TB. This sets the peak output current of the sine/cosine
waves. The specified motor current (which is the unipolar value) is multiplied by a factor of 1.0,
1.4, or 2.0 depending on the motor configuration (series, half-coil, or parallel).
Step Motor Configurations
Step motors can be configured as 4, 6, or 8 leads. Each configuration requires different currents.
Refer to the lead configurations and the procedures to determine their output current.
WARNING!
Step motors will run hot even when configured correctly. Damage may occur to the
motor if a higher than specified current is used. Most specified motor currents are maximum
values. Care should be taken to not exceed these ratings.
6 Lead Motors
When configuring a 6 lead motor in a
half-coil configuration
(connected from one end of the coil
to the center tap), multiply the specified per phase (or unipolar) current rating by 1.4 to determine
the current setting potentiometer value. This configuration will provide more torque at higher
speeds when compared to the series configuration.
When configuring the motor in a
series configuration
(connected from end to end with the cen-
ter tap floating) use the specified per phase (or unipolar) current rating to determine the current
setting potentiometer value.
4 Lead Motors
Multiply the specified
series
motor current by 1.4 to determine the current adjustment potenti-
ometer value. 4 lead motors are usually rated with their appropriate series current, as opposed
to the
Phase Current
, which is the rating for 6 and 8 lead motors.
July 2018
