Datasheet

QSH2818 Manual (V1.02 / 13-November-2007) 9
Copyright © 2007, TRINAMIC Motion Control GmbH & Co. KG
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 fittin
g
volta
g
e in this ran
g
e usin
g
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 exceedin
g
this value, the ma
g
netic switchin
g
losses in
the motor reach a relevant ma
g
nitude and the motor mi
g
ht
g
et too hot at nominal current. Thus there is no benefit in
further raising the voltage.
Table 5.2: Driver supply voltage considerations
Hints:
Q: How to determine if the given driver voltage is sufficient?
A1: Just listen to the motor at different velocities. Does the “sound” of the motor get raucous or
harsh when exceeding some velocity? Then the motor gets into a resonance area. The reason is,
that the motor back-EMF voltage reaches the supply voltage. Thus, the driver can not bring the full
current into the motor any more. This is typically a sign, that the motor velocity should not be
further increased, because resonances and reduced current affect motor torque.
A2: Measure the motor coil current at maximum desired velocity.
For microstepping: If the waveform is still basically sinusoidal, the motor driver supply voltage is
sufficient.
For Fullstepping: If the motor current still reaches a constant plateau, the driver voltage is sufficient.
If you determine, that the voltage is not sufficient, you could either increase the voltage or reduce
the current (and thus torque).