If your motor has stopped working or is nuisance tripping then you may be able to diagnose the problem by performing a few basic checks.
Before starting with the investigation it would be worth noting the general condition of the motor. Look for broken mounts/parts, signs of burning/carbon, contamination from various sources (water, oil, grease, rust etc)
If the motor can be pulled away from its drive then find out if the shaft will rotate by hand without difficulty. If not, then there may be a mechanical obstruction or failed bearings.
Once the motor has been safely disconnected from the supply then you can take resistance measurements at the main terminals.
Steps To Determine If Your Motor Needs a Rewind?
1. Firstly, a measurement of the winding resistance may indicate if there are shorted coils present. The expected resistance should be available from the nameplate, manual or from the Manufacturer. Resistance is temperature sensitive so you could see a different ohm reading on your meter depending on the ambient temperature or temperature of the winding if it has been operating. Correction for the actual ambient conditions can be made and then compared with the measurement taken. If the measurements are not as expected then a rewind may be needed.
2. Secondly, the insulation resistance (IR) can be measured between windings and also between windings and the earth/ground point. If using a ‘Megger’ instrument using 500V, then precautions will need to be taken to protect any thermistors that may be fitted in the winding. Ideally, the IR value should be a minimum of 2M ohms and preferably greater than 100M ohms. If the value is 2Mohms or less it is an indication that the insulation is deteriorating or has already failed.
The majority of winding faults will be due to low IR. This may be for various reasons – its age, damaged wires, contamination, power surges, excessive heat/overloads and vibration. In some cases it is possible to improve the insulation resistance by a thorough clean and drying out in a suitable oven.
Talk to the rewinding experts
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