DC Motor Glossary

Alternating Current (AC) The type of power available from the national grid UK.

Altitude Listed kW rating are based on motors operating at an altitude not exceeding 1,000 metres above sea level.

Ambient Temperature (AMB) Listed kW rating are based on motors operating in an ambient temperature (surrounding air temperature) not exceeding 40 degree C.

Ampere (Amp) The standard unit of electrical current.

Armature In DC brushed motor other than brushless DC machines, it is rotating, and is known as the rotor.

Bearings:- Ball Ball bearings are specified in standard DC Motors.

Roller Roller bearings can be specified when high axial thrust is encountered such as the fitting of pulleys.

Brush Is the current conducting material in a DC motor, and is usually housed in the brushgear and is spring loaded onto the commutator and allows the current to flow into the armature, brushes wear and require regular inspection and replacement.

Brushgear The part of the motor that locates the brushes with brush holders on the commutator the brush is held on the commutator with a constant pressure spring.

Commutator Is the part of the armature that the brushes sit on it allows the current to flow into different segments of the commutator which in turn provide switching to the armature winding's and creates torque and rotation.

DC Current Is the type of current available from batteries, dynamo’s (not alternator), or a DC Drive

Continuous Duty IEC states that S1 is continuous duty the motor works at a constant load for enough time to reach temperature equilibrium.

Intermittent Duty IEC states that S3 is intermittent periodic duty. Identical run and rest cycles done in sequence with constant load. Temperature equilibrium is never reached. Starting current has virtually no effect on temperature rise.

Efficiency the ratio of the energy developed by a motor, to the energy supplied to it, usuallyexpressed as a percentage.

Enclosure The type of motor body an example it could be described as TEFC Totally Enclosed Fan Cooled.

Encoder A digital feedback device that is normally mounted on the non-drive end of the motor and feeds pulses back to digital DC drive to maintain speed.

Endshield A motor typically has two end shields a drive end and a non drive end they house the bearings for the armature or rotor to rotate in.

Excitation A DC Motor with field coils, the current must flow in the coils to generate the field. This generating a magnetic field by means of an electric current is referred to as excitation.

Field - Is the part of the electric motor that surrounds the armature it is a magnetic field created by permanent magnets or field coils and control the motor from running out of control.

Frame Size Have been standardised by NEMA and IEC and are refer to the physical size of the motor, an AC motor having an IEC 71 frame size would be 71mm from the bottom of its feet to the center of the output shaft normally an AC motor of IEC dimensions will be interchangeable with any other brand. Beware DC motors do not have an IEC standard and may not interchange.***

Full Load Current (FLC) Is the current drawn by a motor in Amps when being used at the ratings on the name plate it helps you select the correct size drive to run the motor.

Full Load Torque Is the torque produced by the motor when operated at the name plate ratings.

Hertz A standard SI measure of frequency is Hertz, abbreviated Hz. It means “cycles per second.”in electricity the UK is 50Hz and the USA 60Hz.

Horsepower (HP) units of measurement of power and equal to 745 watts.

IEC (International Electrotechnical Commission) An international standards organisation.

Kilowatt:An SI unit of power = to 1000 watts.

Load The work required of a motor to drive attached load.

Expressed in Kilowatts(kW) or torque (Nm) at a certain motor speed.

Mounting Common Mounting’s are B3 Foot Mounted, B5 Flange Mounting, B35 Foot and Flange Mounting, B14 Face Mounted.

Output Shaft is located at the drive end and rotates the load.

Polarity In a DC (direct current) circuit, one pole is negative, the other pole is positive and the electrons flow in one direction only.

Rotation Is the direction the output shaft turns, it can clockwise or anti-clockwise it is usually determined by looking at the motor from the drive end that is the output shaft is pointing towards your nose.

Service Factor Is found on NEMA nameplates and does not appear on IEC nameplates and is an indication of the overload the motor can stand e.g. SF1.15 = 15% overload.

Tachogenerator An analogue feedback device normally located on the non-drive end of the motor it feeds a voltage that is proportional to speed back to the DC drive to maintain speed.

Temperature Rise The amount by which an electric motor, operating under nameplate rated conditions, is hotter than its surrounding ambient temperature.

Thermal Protection Is a device often placed in the windings of the motor to detect overheating and is connected to a relay that trips the motor in the event of overheating to save the motor from serious damage.

Torque The turning effort or force applied to the output shaft, usually expressed in newton meters (Nm)

Starting Torque Force produced by a motor as it begins to turn from stationary and accelerates a DC Motors usually have very good starting torque.

Voltage Is a measure of the energy carried by the charge.

Watt Is a SI unit used to measure power, equal to one joule per second. In electricity, a watt is equal to current (amperes) multiplied by voltage (volts).