QSH-4218 Datasheet, PDF (10/13 Pages) TRINAMIC Motion Control GmbH & Co. KG. – QMOT STEPPER MOTORS

QSH4218 Manual (V1.06/2011-APR-12)
10
6.2.1 Choosing the optimum current setting
Generally, you choose the motor in order to give the desired performance at nominal current. For
short time operation, you might want to increase the motor current to get a higher torque than
specified for the motor. In a hot environment, you might want to work with a reduced motor
current in order to reduce motor self heating.
The Trinamic drivers allow setting the motor current for up to three conditions:
- Stand still (choose a low current)
- Nominal operation (nominal current)
- High acceleration (if increased torque is required: You may choose a current above the
nominal setting, but be aware, that the mean power dissipation shall not exceed the
motors nominal rating)
6.2.2 Choosing the standby current
Most applications do not need much torque during motor standstill. You should always reduce the
motor current during standstill. This reduces power dissipation and heat generation. Depending on
your application, you typically at least can half power dissipation. There are several aspects why
this is possible: In standstill, motor torque is higher than at any other velocity. Thus, you do not
need the full current even with a static load! Your application might need no torque at all, but you
might need to keep the exact microstep position: Try how low you can go in your application. If
the microstep position exactness does not matter for the time of standstill, you might even reduce
the motor current to zero, provided that there is no static load on the motor and enough friction in
order to avoid complete position loss.
6.3 Motor Driver Supply Voltage
The driver supply voltage in many applications cannot be chosen freely, because other components
have a fixed supply voltage of e.g. 24V DC. If you have the possibility to choose the driver supply
voltage, please refer to the driver data sheet and consider that a higher voltage means a higher
torque at higher velocity. The motor torque diagrams are measured for a given supply voltage. You
typically can scale the velocity axis (steps/sec) proportionally to the supply voltage to adapt the curve,
e.g. if the curve is measured for 48V and you consider operation at 24V, half all values on the x-Axis
to get an idea of the motor performance.
For a chopper driver, consider the following corner values for the driver supply voltage (motor
voltage). The table is based on the nominal motor voltage, which normally just has a theoretical
background in order to determine the resistive loss in the motor.
Comment on the nominal motor voltage:
(Please refer to motor technical data table.)
U_{COIL_NOM} = I_{RMS_RATED} * R_COIL
Parameter
Minimum driver
supply voltage
Optimum driver
supply voltage
Maximum rated
driver supply
voltage
Value
2 * U_{COIL_NOM}
≥ 4 * U_{COIL_NOM}
and
≤ 22 * U_{COIL_NOM}
25 * U_{COIL_NOM}
Comment
Very limited motor velocity. Only slow movement without
torque reduction. Chopper noise might become audible.
Choose the best fitting voltage in this range using the motor
torque curve and the driver data. You can scale the torque
curve proportionally to the actual driver supply voltage.
When exceeding this value, the magnetic switching losses in
the motor reach a relevant magnitude and the motor might
get too hot at nominal current. Thus there is no benefit in
further raising the voltage.
Table 6.2: Driver supply voltage considerations
Copyright © 2011, TRINAMIC Motion Control GmbH & Co. KG