30 November 4, 2009
Drive Current
This parameter sets the current level in the winding when the motor is running. If the Chopper
mode is used, then the chopper switches the voltage to the winding off and on in order to maintain
this current level. If the PWM mode is used, then the duty cycle is calculated to maintain this
current level.
This value should not necessarily be set to the rated current of the winding. For an unloaded
motor, the best current setting varies with motor speed, with less current needed for running at
lower speeds.
Caution – If the motor is run for long periods of time with currents approaching the rated current
for the winding, the motor can become very hot. Use caution around the motor if a heat sink is not
being used.
Holding Current
This parameter sets the current in the winding when the motor is not running. By applying current
to the winding when the motor is stopped, the holding torque of the motor can be increased.
Typically, this should just be a fraction of the drive current, or zero.
Control Mode
This parameter specifies Chopper mode or PWM mode. Chopper mode monitors the winding
current while the winding is on. When the current reaches the target value (Drive Current), it
switches the winding off. The winding remains off for the Off Blanking Time. At the end of the
blanking time, the winding is turned on again, and the current monitoring resumes.
In Open-loop PWM mode, the duty cycle is calculated to set the voltage applied to the winding
such that the target Drive Current flows in the winding. However, this is for a steady state situation,
and when the motor is turning, its impedance changes dynamically. This means that the PWM
current control is not precise. Also, by applying less than the full bus voltage to the winding when it
is turned on, it can take a long time before the drive current is reached. For this reason, the
winding can be left with full voltage applied for a duration at the start of a step. This is controlled by
the Fixed Rise Time parameter.
When using Open-loop PWM mode, current monitoring is not available.
ID Units Range Default
PARAM_DRIVE_CURRENT mA 100–3000 1500
ID Units Range Default
PARAM_HOLDING_CURRENT mA 0–3000 0
ID Units Range Default
PARAM_CONTROL_MODE choice Chopper, Open-loop or
Closed-loop PWM
Chopper
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