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When a motor burns out, the decision is not just the repair price: a rewound motor usually runs a little less efficiently and uses more energy for the rest of its life. Compare the annual cost of each path and find out in how many months the new motor pays for itself.
Pre-sizing and estimating tool: the results do not replace a design, calculation, or report signed by a qualified professional, nor verification against the applicable standards.
Technical responsibility. This calculator is under verification. The reference values and examples are hypothetical, to illustrate the calculation, and are not technical references. The user is responsible for the data entered, the choice of parameters, and the use of the results, and must validate them with a qualified professional before any decision, purchase, application, or construction work.
How to read: each bar is the total annual cost of keeping the motor running, adding up the investment spread over its useful life (light part) and the energy bill (dark part). Lower is better. A new motor usually costs more to buy and less to run.
How to read: each line is the annual cost of one option for different hours of operation. The rewound motor starts cheaper and rises faster, because it uses more energy. Where the lines cross, both options cost the same; to the right of the crossing, the new motor pays off. The vertical line is your case.
How to read: each line adds up what you have spent since the day of the decision (investment plus energy, without interest). The new motor line starts higher; where it crosses the rewound motor line, the extra investment has paid back (payback). If the crossing comes after the rewound motor's useful life, it is not worth it.
Columns: the rewinding option, the new motor option and the difference (new minus rewound). Positive values in the cost difference mean the new motor is more expensive; negative values mean it is cheaper.
Drag the controls to simulate data different from what you entered (from 30% less to 30% more) and watch the result change instantly.
Equivalent annual cost of the rewound and new motor for different hours of use per year, with the other data entered.
The calculation done in steps, with the values you entered.
Power with margin for flows of 20 to 120 m³/h at the head you entered; the dot is your flow.
Annual energy spending with the rewound motor and with the new motor.
Cash flow: investment in the new motor, net of rewinding, in year 0, and annual energy savings adjusted by the entered tariff and discounted at the TMA.
The calculation memo gathers this page's inputs, results, equations, assumptions, and references, with fields for project, responsible person, and review. The full report also includes the charts and interpretations, in color. In the print window, choose Save as PDF.
The page has two parts. The first, rewind or replace the electric motor, compares the annual cost of rewinding the current motor with buying a new motor, based on operating hours, the tariff and the cost of each option, with the cumulative spending over the years and a year-by-year table. The second, Top-up: pumping and motor replacement, sizes the motor power from the flow rate, the total head and the pump efficiency, and calculates the payback of the replacement.
Use the first part to decide whether to repair the current engine and the second to choose the power of the pump engine.
Hypothetical values, to understand the calculation. They are not technical or market references.
Pump of 60 m³/h at 40 m of head, with 60% efficiency and 15% margin. The hydraulic power is 6.54 kW (60 × 40 × 9.81 ÷ 3,600). At the shaft, 6.54 ÷ 0.60 = 10.90 kW. With the margin, 12.54 kW, and the nearest commercial motor is 15 kW.
Motor replacement: rewinding costs R$ 2,500 and a new motor R$ 4,500, with 92% efficiency versus 78% for the rewound one. With 1,200 h per year and a tariff of R$ 0.90 per kWh, the saving is about R$ 2,297 per year. The difference of R$ 2,000 pays for itself in about 0.9 year.
It depends on the size, the hours of use, and the repair price. For small motors with few hours per year, rewinding usually pays off. For large motors that run many hours, energy costs more than repair, and a new high-efficiency motor tends to win. The calculator does this math with your numbers.
It can get worse. With a well-controlled process, the typical drop is around half to one percentage point; if the old winding is removed without temperature control, it can exceed two points. Ask the workshop for a yield test. Here, the loss is a value you enter.
It is a rule of thumb: if the repair costs more than half, or 60%, of the price of a new motor, the trend is to buy new. It ignores hours of use and tariff, so the page shows the number as a reference and decides by the equivalent annual cost.
It is the total annual cost of each option: the investment divided by the useful life, plus the cost of money, plus the year’s electricity bill. It lets you compare a motor that lasts 8 years with one that lasts 15 fairly.
With a 30 kW motor, 75% load, 6,000 hours per year and a tariff of R$ 0.65 per kWh, the old motor had 90.5% efficiency and, once rewound, drops to 89.5%: it uses about 150.8 thousand kWh per year. The new motor (93.6%) uses about 144.2 thousand kWh. Savings are about R$ 4,300 per year, and the new motor's extra investment of R$ 14,200 pays back in about 40 months. On an equivalent annual cost basis, the new motor is about R$ 2,600 per year cheaper.
If there is a backup motor or another machine to absorb production, the cost of a stoppage is zero and the decision comes down only to repair cost, energy and useful life. If stoppages are costly, the lead time for a new motor and for the workshop becomes very important.
Payback is an estimate based on the values entered. It does not include tariff changes, the risk of a new failure, warranty, or the motor's actual load. Confirm yields and prices with the manufacturer and the workshop, and test more pessimistic scenarios.
Important notice: the Agrocalcs tools make estimates and preliminary sizing based on the data entered and on published engineering methods. They do not replace a design, a calculation report or a report signed by a qualified professional (CREA/ART), nor verification against the applicable technical standards and legislation, such as the Regulatory Standards of the Ministry of Labor. Material and fuel properties vary: check with the manufacturer or with analyses of your process before deciding. By using the site, you agree to the Terms of Use.
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