Types of DC Motors

DC Motors have been a principal service offering at Mawdsleys since the company was founded in 1959.

There are 3 main types of DC motor that are available: Series, Shunt and Compound. These terms relate to the type of connection of the field windings with respect to the armature circuit.

Our blog post takes a look at these three types of DC motor and explains their unique properties and where they might be used.

DC Series Motors

A DC series motor will have its field windings connected in series with the armature. The series winding will have relatively few turns of larger wire or copper strip which are capable of carrying the full load current of the motor. On starting, because the windings are low resistance, a large current can be drawn producing a high starting torque.

This is an advantage for high starting loads such as traction, crane and other heavy applications. The speed of a series motor is dependent on the load, so when the full load current flowing through the circuit has reduced, the speed will have increased.

In some instances, the motors speed could potentially increase to a level above the recommended maximum. For this reason, a series motor should not be connected to its load with a belt.

dc series motor mawdsleys ber bristol

DC Shunt Motors

In a DC Shunt motor the field winding is connected in parallel (shunt) with the armature. The shunt winding is wound from many turns of small copper wire and since it is connected across the DC field supply, its field current will be constant.

The motor will run up to rated speed and this will not be greatly affected by a change in load. The starting torque will be less than a similar sized series motor but if this is not required then a constant speed shunt motor may be preferable for the application.

DC shunt motors can be used for many applications such as plastics or wire extrusion. We carry a stock of small DC shunt wound motors in IP23 IC06 format (drip proof force ventilated). Other DC motors can be made on request.

DC shunt motor with no obvious signs of damage Mawdslets BeR

DC Compound Motors

With a DC compound motor, the majority of the field is wound for a shunt field but with a few turns of series winding on top. The shunt is connected across the field supply and the series turns are connected in series with the armature. This provides a motor with a combination of the shunt and series characteristics.

The starting torque will be higher than a shunt motor but not as high as a series motor. The speed will change with load and the amount will depend on the % of field space allocated to the series winding. The series field can be arranged to either increase or decrease the speed with load. Applications for these motors vary but are often for larger applications such as unwind brake generators, conveyors, mixers etc.

A form of DC compound motor can also be used where the supply is from batteries with a wide range of volts. In this instance both the field and armature have the same voltage applied and by using the compound winding this helps to keep the speed within an acceptable range.

special dc compound motor mawdsleys ber bristol motor overhaul and rewinds

Common Faults In DC Motors

DC motor failure can lead to reduced efficiency and even complete downtime in some operations. Some of the most common issues which cause DC motors to fail include:

  • Carbon brush wear 
  • Carbon dust
  • Commutator surface wear
  • Failed commutator
  • Excessive noise and vibration
  • Voltage surges
  • Loose bearings or coils
  • Loose base

The life of a DC motor can be extended by ensuring it is regularly inspected and is regularly maintained by a professional. This reduces the risk of breakdown and save you money in the long run.

Latest DC Motor Case Studies

Complete DC Motor Service 

Whatever the type of DC motor, we can offer either a new build or full rewind and repair service, all of our rewinds and repairs are carried out in our state of the art workshop to improve lead times and reduce costs.

Call us now to find out how we can help you with DC motors on +44 (0) 117 955 2481 or fill out the contact form below and we will get back to you.

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