IE3 Motor Rewind: Efficiency Loss, Cost and New IE3 Purchase Comparison

When the winding of an IE3 motor burns out or fails, the classic question facing businesses is: is it more sensible to rewind the motor or to buy a new IE3 motor? At first glance, rewinding looks cheaper; however, to make the right decision you need to look not only at the immediate rewind fee but also at the efficiency loss, the frame-size threshold, the cumulative effect of repeated rewinds, and the life cycle cost (LCC). In this guide we cover conceptually the effect of rewinding an IE3 motor on efficiency, in which cases rewinding makes sense, in which cases buying a new motor is more correct, and the ways to make the decision soundly.

What Is Rewinding and When Does It Come Up?

Rewinding is the operation of removing the motor's burned or failed winding and replacing it with a new one. Winding failure can arise from causes such as overload, voltage fluctuation, moisture, insulation ageing or bearing-related heating. When the motor stops, the business usually looks for the fastest and most economical solution; and that often looks like rewinding. However, behind this decision lies the question of whether the motor can preserve its efficiency class.

Understanding why the motor failed also affects the rewind decision. If the failure stems from a recurring cause (for example constant overload or a poor environmental condition), merely renewing the winding does not solve the problem; the same failure recurs. We covered failure symptoms and causes in our electric motor failures article, and getting an early warning by monitoring the winding temperature in our winding temperature monitoring article.

How Does Rewinding Affect Efficiency?

IE3 motors are produced with carefully designed winding geometry, high-quality winding material and an optimized iron core to reach the premium efficiency class. During rewinding, it is not always possible to reproduce this precise design exactly. Small differences in winding wire cross-section, number of turns, compaction and insulation quality can typically cause a small drop in the motor's efficiency.

Why Is Efficiency Loss Important?

Even a small drop in efficiency turns into a significant energy cost over time if the motor runs thousands of hours per year. So a rewound IE3 motor, although it looks cheap as an initial investment, may consume more energy over its life due to the reduced efficiency. Therefore, when deciding, you should look not only at the rewind fee but also at the motor's running hours and the effect of the efficiency loss on the annual energy cost. We explained the difference between nameplate efficiency and the real efficiency achieved in the field in our nameplate vs field efficiency difference article.

What Should Be Done to Preserve Efficiency?

If rewinding is unavoidable, to limit the efficiency loss it is important that the winding is done faithfully to the original design, with quality material and correct techniques. However, even with a good rewind, it is difficult to reach the original factory efficiency exactly. Therefore, in high-running-hour, critical motors, a new motor is usually more advantageous for preserving the efficiency class.

Frame-Size Threshold: Does Rewinding Make Sense at Small Power?

One of the most practical criteria in the rewind decision is the motor's frame size and power. In small-power, small-frame motors, the labour cost of rewinding can approach or exceed the price of a new motor. In this case, rewinding becomes economically meaningless; buying a new motor is both faster and healthier in terms of efficiency.

The common approach in the industry is to recommend replacing motors below a certain frame size with a new one instead of repairing them. In large-frame, high-power motors, because the motor's value is high, rewinding becomes more economically sensible. So the general rule is: a new motor at small power, and rewinding evaluated according to conditions at large power. We covered this logic more broadly in our rewind or buy new article. You can examine the frame-size and power match in our frame size and power matching article.

The Cumulative Effect of Repeated Rewinding

If a motor has been rewound more than once over time, each rewind contributes a small drop to its efficiency, and these losses accumulate. An efficiency drop not noticed at the first rewind can become apparent after the second and third. In addition, each rewind operation somewhat affects the motor's overall integrity, because of the heat treatment of the iron core and the disassembly-assembly processes.

Therefore, in a motor that has been rewound several times, switching to a new IE3 motor instead of a fourth or fifth rewind is usually more sensible. The cumulative loss of repeated rewinds quietly raises the motor's total cost of ownership. Knowing the motor's history (how many times it has been rewound) is important data for the right decision. To measure and document the annual saving of switching to an efficient motor, our measuring annual energy saving article offers a useful framework.

New IE3 Purchase vs Rewind: Total Cost (LCC) Comparison

The right decision is not merely comparing the rewind fee with the new motor price, but evaluating the life cycle cost (LCC). LCC considers the purchase cost, the energy cost and the maintenance cost together. Although the purchase cost looks low in rewinding, the increased energy cost due to efficiency loss can erode this advantage over time.

Which Items Are in LCC?

In an LCC evaluation there are three basic items: the initial investment (rewind fee or new motor price), the lifetime energy consumption (dependent on the efficiency class) and the maintenance-failure cost (including downtime risk). In a high-running-hour motor, the energy cost is usually the largest item; that is why preserving the efficiency class is the most decisive factor in the long term. We explained how to calculate the total cost of ownership in our TCO calculation article.

Stock Advantage and Downtime Cost

Another critical factor in the new-motor decision is downtime. While rewinding can keep the motor in service for days, a new IE3 motor supplied from stock can restart production much faster. The cost of a production stoppage is often higher than the motor itself. Therefore, in critical motors, fast supply from stock makes a new motor more attractive. Our critical spare motor list and stock planning article shows the way to reduce this downtime risk.

How Do You Evaluate Rewind Quality?

If you have decided to rewind, the quality of the rewind directly determines the outcome. A good rewind shop records the original winding data (wire cross-section, number of turns, connection diagram), removes the winding without damaging the iron core, uses quality winding wire and material of the correct insulation class, and verifies the motor with insulation tests after rewinding. Skipping these steps both increases the efficiency loss and causes the motor to fail again early.

After rewinding, an insulation resistance measurement must always be done, and the motor should be run at no load to check vibration, heating and current values. We explained how the insulation resistance and megger test are interpreted on a stock or repaired motor in our insulation resistance and megger test article. You can examine the effect of the winding and insulation class on life in our winding and insulation class (F/H) article.

Solving the Root Cause of the Failure

Regardless of the rewind or new-motor decision, the real problem to be solved is often why the motor failed. If the failure stems from a root cause such as constant overload, poor cooling, voltage fluctuation, moisture or inadequate protection, both a rewound and a new motor will meet the same end. Therefore, identifying and eliminating the root cause of the failure before renewing the motor ensures the investment is not wasted.

For example, if there is constant overload, you need to select the motor one power level up or review the load. If there is a cooling problem, the motor's installation environment and the cleanliness of the cooling fins are important. If protection is inadequate, you need to review devices such as thermal relays, fuses and winding temperature protection. We covered motor protection devices in our thermal, relay and fuse selection article. You can find how correct sizing prevents failure in our motor load ratio and correct sizing article.

When to Replace, When to Rewind?

In summary, the decision logic can be built as follows: if the motor is small-power and small-frame, high-running-hour and critical, has been rewound more than once before, or the failure stems from a recurring cause, a new IE3 motor is usually the more correct choice. Conversely, if the motor is large-frame and high-value, in a low-running-hour and non-critical point, and is being rewound for the first time, a quality rewind can be evaluated economically.

In any case, when making the decision you need to evaluate the motor's running hours, history and criticality in the application together. We covered the return of replacing an old standard motor with a more efficient model in our replacing the old motor with IE4 article. When choosing a new IE3 motor, for the most sought-after power and speed combinations you can look at our IE3 stock guide article, and for product categories you can visit our efficient electric motors page and our home page.

Frequently Asked Questions

Does rewinding preserve the IE3 efficiency class?

In most cases it does not preserve it exactly. The IE3 efficiency class depends on a precise factory design; in rewinding, small differences in winding geometry and material quality can typically reduce efficiency somewhat. A good rewind limits the loss, but reaching the original factory efficiency exactly is difficult. In high-running-hour motors this difference is important.

Should I rewind my small-power motor?

Usually no. In small-power, small-frame motors, the rewinding labour can approach or exceed the new motor price. In this case a new motor is both more economical and healthier in terms of efficiency. Rewinding becomes sensible mostly in large-frame, high-value motors.

If my motor has been rewound before, can I rewind it again?

Although technically possible, each rewind contributes a small loss to efficiency, and these losses accumulate. In a motor that has been rewound more than once, switching to a new IE3 motor is usually more correct. Knowing how many times the motor has been rewound helps you make the decision soundly.

Get a Quote

When deciding between rewinding your failed motor and buying a new IE3 motor, contact us with the motor's power, speed and application information; we will evaluate the suitable IE3 motor option and fast-supply possibility based on stock availability. For a fast quote and technical support, reach us at +90 (532) 345 49 86 or send your request through our contact page.

Decision Checklist

• Do the motor's power and frame size make rewinding economical?
• How many hours per year does the motor run; is efficiency loss important?
• How many times has the motor been rewound before?
• Does the failure stem from a recurring cause?
• Is the motor at a critical point; is the downtime cost high?
• Have you compared the rewind fee with the new motor price in terms of LCC?
• Is fast supply from stock possible?
• Does preserving the efficiency class provide saving in the long term?