Motor Rewinding Procedures
Alternating current (AC) and direct current (DC) motors employ an insulated, current-carrying coil essential to their operation. The traditional method for motor rewinding involves removing the old coil, winding a new coil and varnishing.
Removal
Old coils are removed by heating the stationary part of the motor (stator) in an oven. The stator is kept in the oven at temperature of 650 degrees Fahrenheit for at least 10 hours or until the winding insulation turns to ash.
Winding
New coils are traditionally wound by hand by a technician on a coil winding machine. The technician controls the wire tension, layering and number of turns on the coil, although there is also a mechanical counter on the machine.
Varnishing
The newly rewound coil is warmed in an oven, immersed in an epoxy varnish and baked in an oven at a temperature of 300 degrees Fahrenheit for at least four hours. This procedure is known as dip and bake.
Can any motor be rewound?
Whether a motor can be rewound using the usual motor rewinding formula depends on the type of damage that has caused it to burn out. The most important part of any electric motor is its stator core. This core is a fixed stator with a rotating armature inside it. It consists of two main parts: windings of copper wire, and insulated and stacked iron laminations.
Prolonged overheating, excessive one-time heating, or water inside the motor can result in the stator winding insulation failing. This type of malfunction rarely damages the core, and can easily be fixed by taking out the ruined winding and replacing it with a new one. On the other hand, should a motor fail due to a bearing failure, it’s likely that the stator core will be damaged by the iron armatures grinding against the stator iron. In this case, rewinding is usually impossible, and the motor has to be replaced since it won’t start at all.
Motor rewinding basics – is rewinding always worth it?
Sometimes, a motor can be repaired or rewound, but it may not be worthwhile to do so. Very old units (10+ years), or ones that have been incorrectly rewound in the past, should be replaced with a new motor. Another thing to consider is the operating cost. Older models generally have a higher operating cost than newer, energy-efficient models. Paying a larger sum upfront for a modern motor could save you more money in the long run than rewinding the older, inefficient motor and continuing to pay higher operating costs.
Many people disregard these motor rewinding basics and automatically decide to have their motors rewound because it saves them money in the short term. This can cause considerable issues later on. Failure to ensure the stator core is undamaged before attempting rewinding is a typical mistake. Doing so usually results in a motor with lower efficiency, greater risk of another burnout, and much worse thermals.
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