Technical information - Dunkermotoren GmbH

Technical Information

Attention! Following information only apply for direct current motors of the series BG and GR/G.

DC motors

For many applications, it is sufficiently accurate to take the most important data from the motor characteristic diagrams and data tables. Although tolerances and temperature influences are not taken into account, the data is accurate enough for approximate calculations. The degree of protection quoted relates only to the housing – adequate sealing of the shaft is the responsibility of the customer.

The values in the data tables are according to EN60034 and base on a „detached“ motor, which means mounted thermally insulated to a flange. Under real operating conditions, the nominal torque of the motor is much higher in most cases because a direct connection to the flange results in better heat dissipation.

  • Nominal voltage UN (VDC)
    The DC voltage that is applied to the commutation electronics as a system supply voltage. All rated data in our catalogues are with reference to this voltage. Motor applications are, however, not restricted to this voltage.
  • Rated current IN (A)
    The current drawn from a DC source when the motor is operating at rated torque. (1)
  • Rated torque MN (Ncm)
    The torque that can be produced by the motor, operating continuously, in an ambient temperature of 20°C. (2)
  • Rated speed nN (min-1)
    The speed of the motor when it is operating at rated torque. (3)
  • Friction torque MR (Ncm)
    Torque threshold that needs to be overcome, in case the non-powered has to be moved (is only specified for G/GR motors – relevant for self-locking)
  • Holding torque MA (Ncm)
    Maximum Torque that is generated at speed 0. (4)
    In some cases this is a theoretical value, e.g. if the integrated electronics limits the torque or if the motor is demagnetised at lower currents. Then, the maximum possible Value is specified. (4a)
  • No-load speed (rpm)
    Speed that is reached if the corresponding nominal voltage is applied to the motor without mechanical load. (5)
  • Rated power PN (W)
    The output power which the motor can produce continuously; it is calculated from rated speed and rated torque.
  • Maximum output power Pmax (W)
    Maximum mechanical output power the motor can generate at nominal voltage. This power can only be generated for a limited period.
  • Torque constant Ra (N/A)
    Represents the correlation between input current and output torque.
  • Connecting resistance Ra (Ω)
    Typical ohmic connecting resistance phase to phase (BG motors) or between (+) and (-) (G / GR motors).
  • Connecting inductance La (mH)
    Typical connecting inductance phase to phase (BG motors) or between (+) and (-) (G / GR motors).
  • Peak current Imax (A)
    The maximum current for electronics or motors with integral electronics. (6a)
  • Starting current Imax (A)
    The current required to produce the starting torque. For motors with electronics, the starting current may be higher than the permissible peak current.
  • Rotor moment of inertia JR (gcm2)
    The moment of inertia of the rotor is the factor that determines the dynamic properties of a motor.
  • Motor weight mM (kg)
    Motor weight without gearbox and connecting cable.
  • Speed curve (blue)
    This curve shows the speed characteristic at constant voltage. Its end points are the no-load speed n0 (5) and the theoretical starting torque MA (4).
  • Current curve (black)
    The current curve shows the relationship between current and torque. Its end points are the no-load current I0 (7) and the starting current IA (6).
  • Efficiency curve (green) η
    The efficiency is the relationship between the mechanical power output and the electrical power input. The curve shows the efficiency with the motor in cold condition; as the motor warms up, the curve shifts accordingly.
  • Rated torque MN; Starting torque Mmax
    The rated torque (red) is the limit of the continuous operation region (shaded blue). In the region between the rated torque and the maximum permissible torque, the motor must only be used intermittently (shaded orange). Operating conditions above the maximum permissible torque result in demagnetization of the permanent magnets (shaded red).


When dimensioning the motor-gearbox-combination, it must be ensured that the specified values are not exceeded. If one of these values is exceeded, the result may be a reduced service life. If necessary, the motor torque must be reduced by current limitation and/or the unit must be mechanically protected against overload. The service life of gearbox units can also vary considerably depending on temperatures, acceleration torques and times, vibration and external impact forces. If, due to the application, designs with other materials or other lubricants are used, this can have a further influence on the service life. A comprehensive specification is available for each gear unit in addition to the catalogue specifications.

  • Gear ratio
    The gear ratio is the ratio between gearbox input speed (motor speed) and gearbox output speed.
  • Duty cycle
    The duty cycles for Dunkermotoren gearboxes are defined according to the DIN EN 60034-1 standard. The operating mode S1 describes continuous operation with constant load. The operating mode S8 describes an uninterrupted periodic operation with load and speed changes. Further specification values to be considered for S8 operation are the duty cycle, the allowed permanent output power, maximum intermittent output power, allowed nominal input speed, maximum input speed and the maximum acceleration torque. In the validation
    of the gearboxes for the S8 operating mode, a duty cycle of 15 s is selected as standard, whereas the pause duration varies depending on the test.
  • Nominal torque
    The nominal torque is the maximum torque that can be transmitted permanently from the gearbox in relation to the gearbox output shaft.
  • Max. acceleration torque
    The maximum acceleration torque is the maximum torque that can be transmitted by the gearbox for a short time in relation to the gearbox output shaft, e.g. during starting or braking of a motor. The definition for "short-term" is within max. 1 second and within max. 3% of the service life. These values refer to an alternating load.
  • Emergency stop torque
    The emergency stop torque is the maximum torque with which the gearbox may be stressed statically and a maximum of 100 times alternately in relation to the gearbox output shaft. Already a single overload can lead to irreparable mechanical damage.
  • Allowed permanent output power
    The allowed permanent output power (green line diagram) is the maximum mechanical power that can be transmitted permanently at an ambient temperature of 20°C in relation to the gearbox output shaft. In intermittent operation, the time average of the output power must not exceed the allowed permanent output power.
  • Max. intermittent output power
    The maximum intermittent output power is the maximum mechanical power that can be transmitted in relation to the gearbox output shaft in intermittent operation during the total duty cycle and at an ambient temperature of 20°C. The maximum duty cycle is limited to 15 seconds.
  • Max. efficiency
    The efficiency is achieved when the gearbox is loaded with the nominal torque and is valid for new condition. The specified efficiency is the efficiency of the complete gearbox and not only the efficiency of the gear toothing. In addition to the toothing efficiency, the gearbox efficiency also takes into account the power losses in bearings and seals.
  • Max. axial load
    The maximum axial load is the maximum force which may act axially on the gearbox output shaft. This force may be applied, for example, dynamically during operation as well as statically when a coupling is pressed on. The axial load refers to a reference speed of 100 rpm at the gearbox output shaft.
  • Max. radial load
    The maximum radial load is the maximum force which may act radially on the gearbox output shaft at the specified distance from the screw-on face. The screw-on face of the gearbox is the surface against which the gearbox is in contact with the customer application. The radial load refers to a reference speed of 100 rpm at the gearbox output shaft.
  • Allowed nom. input speed
    The allowed nominal input speed is the maximum speed at which the gearbox can be permanently driven.
  • Max. input speed
    The maximum input speed is the maximum speed at which the gearbox can be driven for short-term periods. The definition for "short-term" is within max. 10% of the service life.
  • Operating temp. range
    The operating temperature refers to the temperature measured at the gearbox housing. An operation outside of the specified operating temperature range is not permitted. The lower tolerance limit of the operating temperature range can optionally be reduced to -40°C by using a low-temperature grease.
  • Max. backlash
    The maximum backlash is the maximum angle of rotation of the gearbox output shaft when the input shaft of the gearbox is blocked and when the output shaft is turned from stop to stop. Depending on the gearbox design, a specific test torque is specified. The maximum backlash is valid in new condition and at an ambient temperature of 20°C.
  • Lifetime
    The gearboxes of Dunkermotoren are validated in the product qualification with regard to service life. The gearboxes are tested in service life tests according to internal test criteria. The service life depends strongly on the operating parameters and the ambient conditions. For this reason, a general lifetime estimation is not possible.

Applicable is:

MN-Mo x i x ηGe ≤ MN-Ge
MAcc-Mo x i x ηGe ≤ MAcc-Ge

MN-Mo = Nominal Torque of Motor
i = Ratio of Gearbox
ηGe = Efficiency of Gearbox
MN-Ge = Nominal Torque of Gearbox
MAcc-Mo = Acceleration Torque of Motor
MAcc-Ge = Acceleration Torque of Gearbox

Based on the calculations it might be necessary to reduce the motor torque by limiting the motor current in order to bring it into the specified range. Another option is to add a coupling to the output-shaft of the gearbox and therefore make sure the gearbox is not overloaded.

Drive dimensioning
In the wide range of Dunkermotoren products, you will find a suitable drive for almost any requirement in the power range of 1 - 4000 Watt.

The following points should be taken into account when selecting motors and gearboxes:

  • Which operating mode is used (continuous operation = S1 or periodic operation = S5)?
  • What is the expected working life of the motor?
  • Which torque and which speed are required?
  • How much space is available for the motor?
  • What is the available supply voltage? DC or AC?
  • Are there special environmental conditions (temperature, humidity, vibration, ...)?
  • To what degree can heat be conducted away from the motor?
  • Are there exceptional axial and radial shaft loads to be considered?
  • What are the requirements for the motor control electronics?
  • Is the motor to be controlled online via a bus system?
  • Do you need a brake or an encoder?

For dimensioning a suitable motor, determining the required torque plays a decisive role in order to avoid thermal overload of the motor. For combining a drive system consisting of motor and control electronics, it is important to ensure that permissible values for the motor are not exceeded by the electronics. Depending on the required output speed, either a motor or a motor-gearbox combination may be selected. The choice of a reduction gearbox will largely depend on the recommended maximum torque in continuous operation. For intermittent duty, loading above the rated torque is possible.

We will be pleased to carry out a precise adaptation of a motor to your operating conditions.

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