Why can the usage of a motor controller be an advantage even for a DC motor?

Topic:

DC motors with brushes can be operated directly at a power supply (or battery).

• What is the advantage if a motor controller is even in use by brushed DC motor?

Solution:

Motors are often in use in combination with a motor controller. In case of a brushless motor this is even mandatory.  In case of brushed DC motor, however, operation directly from a voltage source or battery is possible too. If the voltage is adjustable, the speed can also be varied. The question therefore arises why the use of a motor controller can be still useful for a brushed motor and what advantages result from this?
The following advantages and possibilities result from the use of a motor controller (e.g. like maxon's ESCON product line):

• Improved speed stability
  (e.g. in case of load changes)
  
  
• Simple speed adjustment and speed commanding
  (e.g. by a potentiometer, analog set value, or fixed configured speed values)
  
  
• Configurable speed limitation
  
  
• Configurable acceleration and deceleration ramps
  
  
• Configurable torque limitation (based on current limits)
  
  
• Simple enabling / disabling of the drive
  (e.g. by a digital signal or switch without a complete power-down) 
  
  
• Feedback signals about actual speed or motor current
  
  
• Motor winding protection in case of overload
  based on some thermal model of the motor allowing short-time overload periods and taking the motor's thermal limits into account.

Special aspect: Motor protection and fuse

A simple fuse is not able to protect the motor winding of a DC motor in a reliable way for most applications:

• If the motor winding has to be protected in case of an overload or even a blocked shaft, the fuse's rating (or current limit of a power supply) can in maximum be the value of the motor's specified "Nominal current". The disadvantage of such a "safe" fuse or current limit is that the high dynamics of a motor is not available for fast acceleration or deceleration (which demand for short high current peaks). Another problem ist that powerful motors typically have a very low winding resistance of just 1 Ohm or less. A as a result, high current peaks (I = U/R) occur when the motor voltage is applied spontaneously (without some ramping up). Such current peaks can blow and damage the fuse already at motor start.
• If the fuse has a current rating higher than the motor's specified "Nominal current", it cannot protect the motor winding in case of overload. If there is too much friction, load, or even blockage of the mechanics over a longer period of time, the motor winding can overheat and be damaged by the excessive torque demand (= current flow).

For powerful, high-quality DC motors, the use of a maxon motor controller is also advisable from the point of view of protecting the motor against overload.

• With a correctly configured control system, it is possible to overload the motor several times for a limited short period of time, but still protect the motor winding from a defect caused by an overload state that lasts too long.
• A deliberate overload is necessary in many applications, especially during fast, dynamic acceleration or braking of the drive. maxon motors are often overloaded by such states with 3-5 times of the specified "Nominal current". The maxon controllers make this possible and at the same time prevent the motor from being damaged in the event of a mechanics malfunction (or blockage).
  

Selection of the motor controller?

For simple applications that only require speed and torque control, the maxon ESCON series is typically used. With the ESCON, the speed or torque can be set as a fixed value, via potentiometer, or via an analog or PWM set set value. The motor can be started and stopped via a digital signal with defined ramps (and current limits). The actual speed or the motor current is available as analog output signals if required.

If the controller has to be integrated into a higher-level system and exchange data via an interface (RS232, USB, CAN, EtherCAT), the maxon EPOS4 series can be used.

A short overview of the differences between the ESCON and EPOS series can be found here:
-> ESCON or EPOS: What controller should I select?

Our sales engineers and technical support will be pleased to advise you what controller might fit best to your system design. However, for this we need some details of your application requirements:

• Type of application?
• Part number oft the motor in use (or planned to use)?
• Existing supply voltage?
• Required speed range?
• Typical working point (speed, torque)?
• Need for a bus interface or not?
• Specific environmental conditions?