Do you ever have to make the decision whether to rewind a motor or replace the unit altogether? It’s a tricky decision to make. On the one hand, a rewind is usually cheaper, particularly if the motor is bigger than 5kW or it’s a more specialist motor (such as two speed, or with a DC brake). On the other hand, a new unit is likely to be a longer lasting solution, and in most cases is more energy-efficient as well. This post outlines what’s involved in rewinding a pump, to give some background information to help you make an informed decision.
The picture above shows a typical burnt out motor. The telltale scorch marks on the windings at the bottom right and centre left are the result of the pump motor getting too hot. The only option here is to rewind the motor.
The windings slide out of the casing and measurements can then be taken in preparation for rewinding. This includes details like the wiring of the connections, the wire diameters, the physical dimensions of the profile, and the ‘pitch’ (the pattern of the windings). Information such as the number of ‘poles’ in the motor (which determines rotation speed) is found here, and it’s very important to match this to make sure the motor performance doesn’t change.
After chiselling away the top band of copper, that is at the front of the picture above, the yellow insulation material can be removed. Using a gas burner to heat up the inside means the complete windings can then be removed, leaving just the rotor bars.
Next, it’s sprayed with anti-tracking varnish and the new insulation is put in, cut from long rolls to suit the exact motor size. The motor will be tested later to over a thousand volts more than normal running voltage, and the insulation is built to sustain that.
Finally the rewinding can begin. A ‘form’ to achieve the correct ‘pitch’ is used, and on a complex motor with many windings this can be a time-consuming and laborious task. However, taking care at this stage ensures that the motor will perform with maximum efficiency.
When the motor is reinstated there are several checks carried out, including checking the resistance between the windings and checking the resistance to earth. It’s ‘flash tested’ briefly (where a voltage of 2x normal voltage plus 1000V is put through the motor to check the insulation holds good), and it’s also gradually run up to normal running current with constant measurements taken to look out for any discrepancy. The final product is connected back to the pump head and is ready for installation. We guarantee all rewinds for a year, and usually a rewound motor will in fact last for many years.