User Manual

Global Power Configuration Parameters
Advanced Digital Motor Controller User Manual 87
The time it takes for the heat sink’s temperature to rise depends on the current output,
ambient temperature, and available air flow (natural or forced).
Short Circuit Protection
The controller includes a circuit that will detect very high current surges that are consis-
tent with short circuits conditions. When such a condition occurs, the power transistor for
the related motor channel is cut off within a few microseconds. Conduction is restored
at 1ms intervals. If the short circuit is detected again for up to a quarter of a second, it is
considered as a permanent condition and the controller enters a Safety Stop condition,
meaning that it will remain off until the command is brought back to 0.
The short circuit detection can be configured with the PC utility to have one of three sen-
sitivity levels: quick, medium, and slow.
The protection is very effective but has a few restrictions:
Only shorts between two motor outputs of the same channel are detected. Shorts
between a motor wire and VMot are also detected. Shorts between motor output and
Ground are not detected.
Wire inductance causes current to rise slowly relative to the PWM On/Off times. Short
circuit will typically not be detected at low PWM ratios, which can cause significant heat
to eventually accumulate in the wires, load, and the controller, even though the controller
will typically not suffer direct damage. Increasing the short circuit sensitivity will lower the
PWM ratio at which a short circuit is detected.
Since the controller can handle very large current during its normal operation, Only direct
short circuits between wires will cause a sufficiently high current for the detection to
work. Short circuits inside motors or over long motor wires may go undetected.
A simplified short circuit protection logic is implemented on some controller models.
Check with controller datasheet for details.
Mixed Mode Select
Mixed mode is available as a configuration option in dual channel controllers to create
tank-like steering when one motor is used on each side of the robot: Channel 1 is used for
moving the robot in the forward or reverse direction. Channel 2 is used for steering and
will change the balance of power on each side to cause the robot to turn. Figure 7-2 below
illustrates how the mixed mode motor arrangement.
Controller
FIGURE 7-2. Effect of commands to motor examples in mixed mode