DC  Motor Repair & Rewinding Services

History will recognize the vital role played by DC Motors in the development of industrial power transmission systems, the dc machine being the first practical device to convert electrical power into mechanical power.  Inherently straight forward operating characteristics, flexible performance and high efficiency have encouraged the widespread use of DC motors in many types of industrial Drive Applications. We not only repair and refurbish your motor but to provide root cause failure analysis on why it has failed. We consistently provide electric motor repairs and refurbishments that are better than new motors!

Our comprehensive Electric Motor Service, repairs motors, when you need them, performed to state-of-the art standards. Shop and Field Service support capabilities include 24 hour service, 7 days a week.

Our DC Motor Repair services include:

  • Reconditioning –Repair, reconditioning, and adjustment of the Electric Motor• Field & Armature components’ parts are thoroughly cleaned and baked dry. Replacement of Bearings, Seals and any auxillary componants, as required.
  • Rewinding –Complete refurbishing of the Electric Motor• Armature and Field Coils are rewound using NEMA Class “H” insulation system. Replacement of Bearings, Seals and any auxillary componants, as required.
  • Modifications –We offer application design and assistance, plus the capabilities of modification of New Electric Motors and Generators to meet your specific requirements.
  • Testing – DC Motors are tested using non-destructive winding analysis and testing and test run for proper electrical and mechanical operation. Voltage, Current, Bearing temperature, and Vibration are closely monitored and documented.
We know Motors! Contact us for a Motor Repair Quote, a Replacement Motor, or Predictive Maintenance Plans.

Repair Service for all types of DC Motors of the following designs:

•  Shunt Motors                                                          •  Series & Compound Motors  252045
•  Mill Motors                                                              •  Mining Motors  
•  Hoist/Crane Motors                                            •  Spindle Motors
•  Printing Press Motors                                        •  Specialty Motors
•  Explosion-Proof Motors                                    •  Mixer Motors
  Fan & Blower Motors                                             Permanent Magnet Motors 
•  Conveyor Motors                                                  •  Eddy Current Clutches
•  Varidrives                                                                •  Traction Motors
•  Washdown Motors                                               •  Gearmotors

In any electric motor, operation is based on simple electromagnetism. A current-carrying conductor generates a magnetic field; when this is then placed in an external magnetic field, it will experience a force proportional to the current in the conductor, and to the strength of the external magnetic field.  A basic law of magnetism is that unlike (North and South) polarities attract each other , while like polarities (North and North, South and South) repel. The internal configuration of a DC Motor is designed to harness the magnetic interaction between a current-carrying conductor and an external magnetic field to generate rotational motion.

DC Electric Motors are used in applications from a small, special purpose apparatus to f36f957f72a093559175396d0ab32c18those driving large-scale industrial machinery. The most common type of DC Electric Motor used in Industry is the Shunt Motor. A Shunt DC Motor connects the armature and field windings in parallel or shunt with the common D.C. power source. This type of motor has good speed regulation even as the load varies, but does not have the starting torque of a series DC Motor.

Every aspect of our DC Motor Repair shop, from electric motor rewinding to electric motor part repair, is performed under the stringent quality standards. As a reflection of our uncompromising commitment to customer satisfaction, all of EMX Electric Motors Service work is 100% guaranteed.

Incoming Inspection

EMX Motor Repair Shop performs a thorough appraisal of the motor’s condition, as received, to determine what specific repairs are needed as well as to find unsuspected trouble, perhaps unrelated to the obvious defect. Our technicians diagnose cause and effect to help prevent a recurrence. The motor may have been sent to our Repair Facility with limited external evidence as to the nature and location of trouble. What seems wrong may be correctable in several ways. Our appraisal will include a complete review of the following conditions of each part of the motor: General cleanliness, Cracked or broken welds or castings, Missing hardware, Wear or rub marks, including fretting, discoloration, charring, or other evidence of overheating , Looseness at mating fits, Corrosion, moisture, or oil inside the machine. Digital Photographs of any abnormal conditions found are part of the appraisal process and inspection report. Our DC Motor Repair includes dissassembly, detailed inspections, and measurements to identify electrical and mechanical damage.

Incoming Tests

Prior to an incoming run test, we perform the following and record information where 2016-08-12 08.07.53appropriate: Motor will be mechanically inspected to determine if shaft turns freely, Verify that bearings are lubricated, Insulation resistance tests are performed. As well as , the continuity of Field & Armature windings, condition and installation of brushes, Polarization index (where appropriate). Surge test (where appropriate). If conditions permit, the motor will be run at reduced voltage initially (25-50% of rated voltage). If the test is successful, Results are recorded, and then the motor will be run at full rated voltage, if possible. The intent of the “As Received”, no load, run test is to get the motor operating safely up to top speed for electrical characteristics, bearing temperature, and vibration checks prior to dissassembly. If the “As Received” motor conditions permit, the motor shall be run to 100% speed for these tests.

Disassembly & Inspection

Before any disassembly is begun, parts will be marked (i.e., brackets, frame, covers, and brush holders).  Brackets and bearings will be identified as pairs. Check and record rotor air gap.  Frame-mounted devices will be identified and recorded. Electrical wiring is recorded, sketched, and marked before disconnecting (for external connection).

The condition of the Field & Armature windings and the extent of repairs are determined by inspection and, as necessary, by testing. Coil windings are observed for the following: Slot Wedges (“top sticks”) that are loose, damaged, or have shifted in position. Ties, lashings, or blocking that are loose or broken. Dirt, oil, or moisture deposited on coil surfaces. Coil damage – Besides obvious burning, tracking, or charring, look for loose or cracked tape, coils that have moved within the slot, deposits of dirt or chemicals, and insulation pitted or worn away by airborne abrasive particles. Winding integrity is determined using non-destructive winding analysis and testing. If necessary, the commutator is machined and undercut and Armature windings are examined for evidence of defects. Additional Testing may be required.

Electric Motor components & parts are thoroughly cleaned. Steam cleaning is the preferred method. Shafts will be checked for wear, cracks, scoring and straightness. (NEMA MG 1-2003 Rev.1-2004, Section 1, Part 4 Par. 4.11); cracks, corrosion; scoring or galling. Shaft extensions should be smooth, polished and concentric with the shaft center.  Shaft extension dimensions and permissible runout will be checked and DC MOTOR BASICSDiameter Tolerances for NEMA/IEC frame size machines compared. Keyseat/ Keyway Width Tolerances checked against NEMA/IEC Frame Size machines Tables. Keyseats will be true and accommodate keys to tap fit. If the shaft requires repair, worn surfaces can be restored within our Machine Shop to factory specification. Ball or Roller Bearings (Antifriction bearings) are comprehensively inspected for condition of lubricant; dirt, rust, or moisture; fretting corrosion; thermal discoloration; pitting or spalling of balls, rollers, or races; broken or missing retainers. Sleeve Bearings are checked to  be uniform in diameter, of proper fit in the housing, smooth internally and suitably grooved for adequate distribution of lubricant. Bearing Housings and Shaft bearing fits are measured and compared to manufacturer’s specifications.  Any fits that are not within tolerance are restored to original factory specification. Seals & Seal clearance are set to original equipment manufacturer’s specifications if available. Oils used will compatible with the customer’s lubricant. Frame and Bearing Housings will be examined for defects; Corrosion; structural weld integrity; blocked drains, breathers, or ventilating air passages; paralleling of feet. Cracks and breaks are repaired and fits restored to manufacturer’s specifications.

Electric Motor Accessories, such as, Space heaters are tested for rated current or power and subjected to a high-potential test. They will be replaced if damaged. Bearing temperature sensors or protectors will be identical with or equivalent to the original devices in electrical and thermal characteristics.


EMX’ State of the Art Shop Balancing Systems are designed to perform measurements ofstacks_image_1428 vibrations and calculations in horizontal shop balancing machines and in the field. The application measures the running speed (1X) filtered vibration amplitude and relative phase with a reference mark in the rotor to allow full balancing correction. Dynamic Balancing results are to be performed to the level specified by the customer.  In the absence of a requested level, dynamic balancing to balance quality grade G2.5 (ISO 1940/1) should enable the machine to meet final vibration limits. Note: Balance Weights are to be located so that they do not interfere with other machine components.

Recondition of Field Coils & Armature

Electrical components’ parts are thoroughly cleaned. Steam cleaning is the preferred method. Cleaning will continue until all vent slots are free of any obstruction which may interfere with proper cooling of the motor. Insertion of any metal object into ventilation passages of a Fields or Armature is unacceptable under any circumstances. Prior to an re-insulating application, the windings will be preheated to 110°F to 130°F to remove air and moisture. Oven temperature will not exceed 290°F during the drying cycle for Class “F” or “H” insulation. Oven temperature will not exceed 250°F for Class “A” or “B” insulation. A Final megger reading must exceed 1 megohms at room temperature., at which time either the spray or flow method or the “Dip and Bake” method can be used.  A reading below 10 megohms requires communications with the User and determination will be made as to rewind the Fields or Armature verses the cost of motor replacement.

In the event that Rewinding of Field Coils or Armature is the better choice in the repair of the Electric Motor, the winding will be re-manufactured using an inverter rated magnet Polwicklungen_1wire and the insulation exclusively classified as follows: NEMA Class “H” An insulation system (180°C temperature limit including a 40°C ambient or 140°C rise) that by experience or accepted test can be shown to have suitable thermal endurance when operating at the limiting Class H temperature specified in the temperature rise standard for the machine under consideration. EMX Motor Repair Shop can redesign motors using computer aided motor redesign and assures that all Winding data is thoroughly reviewed for accuracy. The winding should maintain the same electrical characteristics as the original unless redesigned by agreement with, or at the instruction of, the customer. The entire Insulation System, materials, and methods of application should be equal to or better than that used by the original machine manufacturer. All components of the insulation system will be compatible with each other with respect to electrical, mechanical, and thermal characteristics. RTDs or thermocouples are placed within the windings if they were part of the original design or requested to be added by the User. DC Motors are rebuilt using the highest-quality wire, insulation, and varnish materials for long-lasting repairs in the most severe industrial environments.


All mechanical repairs on shafts, bearing journals, end bells, and other equipment are handled in-house by experienced machinists. All Electric Motor assemblies are made in accordance with good machine shop practices. If the shaft requires replacement, a new shaft will be made of A.I.S.I. 4140 Steel HRHT (Hot Rolled Heat Treated). Under special cases, shaft material will be replaced with 316 stainless or User approved material. Motors will be assembled in a manner that will ensure proper fit and alignment. Ball and Roller Bearings are fitted to shafts by heat-expanding the inner bearing race in accordance with the bearing manufacturer’s recommendations, however, not to exceed 250°F, using an oil-bath heater or an induction heater. Check and record air gap. All bolts, nuts, etc., will be replaced as required with SAE grade 5 or better and torqued to Industry standards. On metric fasteners we will use a grade 8.8 or better. All assembled components will be checked to ensure secure fits. All covers on openings in the frames or housings will be fastened in a closed position.

Final Run Test 

Every DC Motor repaired is tested for proper electrical and mechanical operation. Voltage, Current, Bearing temperature, and Vibration are closely monitored and documented.  DC Motors are Run tested at minimum of 60 minutes duration at the rated voltage and until the temperature of the bearings have stabilized (+/- 1°C over 15 minutes). A maximum temperature of 150°F on babbitt bearings shall not be exceeded (unless bearing manufacturer specifies otherwise). On antifriction bearings and on motors with a cooling fan, the bearing housing temperature should not exceed 30°F above ambient temperature for oil lubrication, and 50°F above ambient for grease lubrication. On motors without external cooling fans, the bearing housing temperature should not exceed 50°F above ambient. At no time should the temperature exceed the drop test temperature of the lubricant. A non-load test run will be made on all motors to ensure that all electrical readings do not exceed the Name Plate Data ratings. A written record of all tests and inspection results will be furnished to the user upon completion of repairs.

Completed apparatus will be externally cleaned and painted to specification. Shaft extensions are treated to prevent corrosion. Packaging and Transportation: After completion of the repair and testing, the machine will be packed in a manner suitable for the form of transport to be used.  Packing and transport will be as arranged with the customer. Shaft is Blocked to prevent movement, depending on the type of machine, mode of transport and the distance to be traveled. Where blocking is used, it will be clearly identified. Oil-lubricated machines will be shipped without oil, and the need for lubricant clearly identified.

EMX Benefits

  • Complete Motor Inspection and Cleaning
  • Provide complete failure and documentation to determine the cause of Motor Failure
  • Comprehensive Bearing Inspection and new Bearing Installation
  • Digital pictures available for Inspection
  • Commissioning of your Equipment
  • Non-destructive winding analysis and testing
  • All Rewinds are made using Class “H” Insulation & Inverter Duty Wire
  • Utilize the best available technology in the repair of your Motor.
  • Treat your Motor problems with concern.
Got a Question! Contact us at 856-362-4553 or email to service@electromechanex.com