QSH6018 Manual (V1.08 / 2014-SEP-04)

9

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5.2.1 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)

5.2.2 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.

5.3 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.)

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 5.2: Driver supply voltage considerations

U