Likely causes

What to do

Problem 1:    On initial installation, motor fails to start up.

Motor is incorrectly wired.

Verify that the motor is wired correctly.

No output power from controller.

Measure voltage coming from the controller.

Motor is damaged and the armature is rubbing against the magnets.

Disassemble motor and see if the armature can be realigned by reassembly.  Motor may have to be replaced.

Problem 2:    Motor has been running then fails to start.

Fuse or circuit breaker is tripped.

Replace the fuse or reset the breaker.

Armature is shorted.  Motor may make a humming noise and the circuit breaker or fuse will trip.

Disassemble motor and inspect the armature for a burnt coil.  Inspect the commutator for burnt bars.  If this condition exists, the motor needs to be replaced. 

The brushes may be worn down too far and no longer make contact with the commutator.

Check the brushes to make sure that they are still making contact with the commutator.  Contact manufacturer for brushes.

Controller may be defective.

Verify voltage is coming out of the controller.

Problem 3:    Motor runs but loses power.

Load had increased.

Ensure that the load has not changed.  Measure the amp draw of the motor against the full load amp rating of the motor.  If the amp draw is higher than the rated one, the motor is undersized for the application.

Motor controller not properly set.

Check controller manual for adjustments.  The torque and/or IR compensation settings may need adjustment.

Motor may have an open connection.

Inspect the armature for an open connection.

Brushes may not be seated properly or worn beyond the useful length.

Verify that the brushes are properly seated and measure their length.

Problem 4:    Motor takes too long to accelerate.

Motor controller not properly set.

Adjust the acceleration trim pot of the controller.

Brushes are worn.

Verify brush length.

Bearings may be defective.

Inspect bearings.  Noisy or rough bearings should be replaced.

Problem 5:    Motor runs in the wrong direction.

Incorrect wiring.

Interchange the two motor leads.

Problem 6:    Motor runs OK but has a clicking noise.

Suspect a burr on the commutator.

Remove burr from commutator using a commutator stone.

A

Alternative Current (AC)

The standard power supply available from electric utilities.

Ampere (Amp)

The standard unit of electric current.  The current produced by a pressure of 1v in a circuit having a resistance of 1ohm

Armature

The rotating part of a brush-type direct current motor.

B

Ball Bearings

Used in industrial & agricultural motors.

Breakdown Torque

The maximum torque a motor can achieve with rated voltage applied at rated frequency, without a drop in speed or stalling.

Brush

Current conducting material in a DC motor, usually graphite or a combination of graphite and other materials.  The brush rides on the commutator and forms an electrical connection between the armature and the power source.

C

Centre Distance

A basic measurement for worm gear reducers, measured from the centreline of the worm to the centreline of the worm wheel.

Cogging

Non-uniform or erratic rotation of a direct current motor. 

Commutator

The part of the DC motor armature that causes the electrical current to be switched to various armature windings. 

Current, DC

The power supply available from batteries, generators or rectified sources used for special purpose applications.

D

Duty Cycle

The relationship between the operating time and the resting time of an electric motor.  Motor ratings according to duty are:

Ø  Continuous Duty: the operation of loads for over 1 hour.

Ø  Intermittent Duty: the operation during alternate periods of load and rest.  It is usually expressed as 5 mins, 30 mins or 1 hour.

E

Efficiency

A ratio of the input power compared to the output, usually expressed as a %. 

Enclosure

Used to describe the motor housing. 

Endshield

The part of the motor that houses the bearing supporting the rotor and acts as protective guard to the internal parts of the motor.

F

Field

The stationary part of a DC motor, consisting of permanent magnets.

Frame

Standardized motor mounting and shaft dimensions as established by NEMA or IEC.

Full Load Amperes

Line current drawn by a motor when operating at rated load and voltage.

Full Load Torque

The torque the motor produces at its rated horsepower and full-load speed.

Fuse

A piece of metal, connected in the circuit to be protected, that melts and interrupts the circuit when excess current flows.

G

Generator

Any machine that converts mechanical energy into electrical energy.

H

Horsepower

A measure of the rate of work.

I

Insulation

In motors, classified by maximum allowable operating temperature.  NEMA classifications include:

Class A=105˚C, Class B=130˚C, Class F=155˚C and Class H=180˚C.

K

Kilowatt

A unit of power equal to 1000 watts and appx. Equal to 1.34 horsepower.

L

Load

The work required of a motor to drive attached equipment. Expressed in horsepower or torque at a certain motor speed.

O

Open Circuit

A break in an electrical circuit that prevents normal current flow.

Output Horsepower

The amount of horsepower available at the output shaft of the reducer (gear box).  Output horsepower is always less than the input horsepower due to the efficiency of the reducer.

Output Shaft

The shaft of a gear box assembly that is connected to the load.

R

Resistor

A device that resists the flow of electrical current for the purpose of operation, protection or control.

Rotation

The direction in which a shaft turns is either clockwise (CW) or counter clockwise (CCW).  When specifying rotation, also state if viewed from the shaft or opposite shaft end of motor.

S

Short Circuit

A fault or defect in a winding causing part of the normal electrical circuit to be bypassed, frequently resulting in overheating of the winding and burnout.

Speed Regulation

In adjustable speed drive systems, speed regulation measures the motor and control’s ability to maintain a constant preset speed despite changes in load from zero to 100%.

Stator

The fixed part of the AC motor, consisting of copper windings within steel laminations.

T

TENV (Totally Enclosed Non-Ventilated)

No vent openings, tightly enclosed to prevent the free exchange of air, but not airtight.  Has no external cooling fan and relies on convection for cooling. Suitable for use where exposed to dirt or dampness, but not for hazardous (explosive) locations.

TEFC (Totally Enclosed Fan Cooled)

Same as the TENV except has external fan as an integral part of the motor to provide cooling by blowing air around the outside frame of the motor.

Torque

The turning effort or force applied to a shaft.

Ø  Starting Torque: Force produced by a motor as it begins to turn from standstill and accelerate.

Ø  Full-Load Torque: The force produced by a motor running at rated full-load speed at rated horsepower.

V

Voltage

A unit of electromotive force that, when applied to conductors, will produce current in the conductors.

W

Watt

The amount of power required to maintain a current of 1A at a pressure of 1v when the two are in phase with each other.  One horsepower id equal to 746 watts.

Winding

Refers to the process of wrapping coils of copper wire around a core, usually of steel.  In a permanent magnet DC motor, the winding is the rotating armature.