The 5 stages of an electric motor rewind

From the initial checks to the final lick of paint, we look at what's involved in an electric motor rewind.

Gibbons’ electric motor rewinds service was where it all began for us back in 1969. Here we present the five stages of a motor rewind, from initial checks to that final lick of paint.

1. Preliminary inspection

Once the motor arrives in the workshop the engineer should carry out an initial check to gather as much information as they can. This stage is a vital part of the process as it may reveal important clues as to why the motor has failed. Areas to be aware of include:

Nameplate data

All information from the motor’s nameplate should be recorded as it may be vital when ordering parts or contacting the original manufacturer with a query.

It’s also worth looking out for additional nameplates added to indicate repairs that have already been carried out.

Comments from the customer

When the customer commissions a motor rewind, it’s important to get as much information from them as possible. This can be invaluable when it comes to fault finding, so engineers should find out:

• The environment the motor has operated in, such as ambient temperature and exposure to vibration
• The equipment it has been used to drive
• Whether it has been rewound before
• How often it is started and for how long in each cycle
• The type of starter used.

Results of external inspection

The motor’s outer condition can yield plenty of information, so tell-tale areas to check vigilantly are:

• Cooling air ducts. Should these be blocked then this points towards overheating
• Shaft. A brown/blue discolouration indicates possible overheating or bearing seizure
• Any missing or damaged parts such as seals, the fan (and cover) and the terminal box.

2. Dismantling

Occasionally an engineer will be able to tell from a motor’s outward appearance whether or not it is repairable, but normally it will need to be disassembled and examined fully.

This process requires great care, as components can easily be damaged when taking a motor apart. Parts that are not to be repaired should be kept in a separate container marked with the motor’s serial number. Taking photographs during the deconstruction process can help the engineer when it comes to reassembling the motor.

As the motor is disassembled, the engineer should make a note of:

• Terminal box layout and connections
• Position of end bracket and bearing caps
• Size, type and clearance of bearings
• Orientation of rotor relative to stator
• Position of shaft with respect to the terminal box
• Evidence of water or dirt ingress
• Condition of stator and rotor cores
• State of winding.

3. Removal of winding and cleaning of core

Techniques may differ, but there are generally four phases to this task:

• Record the winding details on data sheets
• Carry out core loss testing
• Remove the old winding
• Clean the stator core to prepare for rewinding.

4. Rewinding the motor

The best way to retain energy efficiency is to duplicate the original winding configuration, with coil extensions kept as short as is practical and the same length of overhang. However, a skilled engineer will be able to choose a different style of winding to match, or even improve, the motor’s original performance.

Once the winding is in place, the coils and leads are connected up as per the original connections. A series of tests are then carried out before the motor is reassembled.

5. Reassembly

If a motor is not rebuilt properly, its efficiency can be compromised, so it’s crucial that this is done with the utmost care:

• Careless handling can cause rotor and stator damage which may lead to core losses
• Bearings should not be excessively greased as this can cause a loss of friction
• The fan must be mounted correctly as an ineffective cooling system could lead to overheating
• When the motor is painted, the engineer should ensure that ventilation openings are kept clear.
  

A rewind should only ever be carried out by an experienced professional, as done incorrectly the motor’s efficiency can be significantly reduced. 

Gibbons offer a free motor rewind collection/delivery service within a 50-mile radius of our workshop in Tollesbury, Essex, so give us a call on 01621 868138 or email info@gibbonsgroup.co.uk and we’ll be happy to help.