Motor doesn't start or draws too much power

1. Introduction

If the motor of a linear drive fails to start or draws unusually high current, the cause must be identified quickly. The reasons can vary widely – from mechanical overload to electrical connection faults. If left unresolved, such issues can lead not only to downtime but also to damage to the motor, brake, or control system. In this article, you will learn what the possible causes may be and which measures help to permanently eliminate the problem.

2. Typical symptoms

Motor-related problems may manifest as:

1. Failure to start (motor does not rotate)
2. Fuse trips when attempting to start
3. Loud humming without movement
4. Slow or jerky start
5. Significantly increased current consumption under load

These symptoms indicate mechanical or electrical issues, which we examine below.

3. Causes

3.1 Overload or incorrect sizing

If the lifting capacity exceeds the planned value, the motor’s starting torque may no longer be sufficient. So, it may fail to start or shut down immediately. The same applies in cases of incorrect sizing: if the motor is undersized, it becomes overloaded as soon as load or friction increases. A temporary fix such as installing a “larger frequency inverter” won't solve the issue since the root cause lies within the mechanical system.

3.2 Incorrect supply voltage

A three-phase motor is designed for a specific mains voltage and frequency (e.g. 400 V, 50 Hz). If operated at an incorrect voltage (e.g. wrong star/delta configuration, incorrect phase sequence, faulty power supply), it may fail to deliver the expected performance or may not run at all. The nameplate and wiring diagram provide clarification.

3.3 Brake doesn't release

Electric motors with holding brakes are braked at standstill – the brake releases only when the correct voltage is applied. If the control wiring is incorrect, the brake voltage is interrupted, or a fuse is defective, the brake remains engaged. This also prevents the motor from starting.

3.4 Mechanical obstruction or fault in the load chain

In rare cases, a mechanical defect (e.g. jammed thread, blocked carriage, or deformed guide) may be the cause. The motor attempts to start but is mechanically prevented from rotating resulting in high current draw or safety shutdown.

4. Corrective measures

4.1 Check load and sizing

1. Compare the actual lifting load with the originally calculated load.
2. Check whether conditions have changed over time (e.g. additional loads, increased friction, added components).
3. If necessary, increase motor power or alternatively use a reduction gearbox: lower speed, higher torque.

Note: The mechanical lifting element (e.g. Spindle or Linear Chain) must also be designed for the higher load.

4.2 Inspect the power supply

1. Check the applied voltage at the motor and brake.
2. Verify phase sequence in three-phase systems.
3. Test the brake control lines. Is the correct voltage present?
4. Refer to the nameplate for rated voltage, current, wiring configuration, frequency, and brake specifications.

4.3 Request technical documentation

1. If uncertainties remain, request wiring diagrams, technical data sheets, or connection instructions from your supplier.
2. Important for brake motors: Is there a separate brake nameplate or external brake control?

4.4 Inspect mechanical components

1. Do all drive components move freely and smoothly?
2. Are there signs of blockage, deformation, or foreign objects in the guide system?
3. If in doubt, rotate the drive unit manually or remove it to check for smooth operation.

5. Conclusion

A motor that fails to start or draws unusually high current is always a warning signal, but with systematic troubleshooting, the cause can usually be identified quickly. Whether mechanical overload, incorrect sizing, or power supply issues: those familiar with the typical weak points can check them systematically and eliminate the problem before major damage occurs. Technical data, nameplates, and a careful review of load and wiring conditions help you reach a solution quickly.