User manual

QSH4218 Manual (V1.11 / Feb 8th, 2006) 9
Copyright © 2006, TRINAMIC Motion Control GmbH & Co. KG
Hints:
Q: How to choose the optimum current setting?
A1: 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)
A2: If you reach the velocity limit, it might be a good idea to reduce the motor current, in order to
avoid resonances occurring. Please see the hints on choosing the driver voltage.
Q: What about energy saving – how to choose standby current?
A1: Most applications do not need much torque during motor stand-still. You should always reduce
motor current during stand still. 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 stand still, 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 stand still, 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.
5.3 Motor Driver Supply Voltage
The driver supply voltage in many applications can not be chosen freely, because other components
have a fixed supply voltage of e.g. 24V DC. If you have to 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: U
COIL_NOM
= I
RMS_RATED
* R
COIL
(Please refer to motor technical data table.)
Parameter Value Comment
Minimum driver
supply voltage
2 * U
COIL_NOM
Very limited motor velocity. Only slow movement without
torque reduction. Chopper noise might become audible.
Optimum driver
supply voltage
≥ 4 * U
COIL_NOM
and
≤ 22 * U
COIL_NOM
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.
Maximum rated
driver supply
voltage
25 * U
COIL_NOM
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 4: Driver supply voltage considerations