Measurement and Evaluation of the Resistance of SEW Brake Coils

SEW motor brakes are widely used in industrial automation, and their brake coils, as the core components of the braking system, play a critical role in ensuring stable equipment operation and safe braking. The resistance value of the brake coil is one of the key indicators for assessing its performance condition. This paper provides a detailed discussion of methods for measuring and evaluating the resistance of SEW brake coils.

Method for Measuring the Resistance of a Brake Coil
1. Preparations

Before measuring the resistance of the brake coil, you will need to prepare the following tools:

Multimeter: used to measure resistance values.
An appropriate test fixture or probe to connect to the wiring terminals of the brake coil.
Refer to the brake model and resistance standard reference table or manual for comparing measurement results.
2. Measurement Procedure

Taking the SEW motor brake model DT71D4/BMG/HF VB=220Vac/5NM as an example, its braking coil typically consists of three wires: white–red, white–blue, and red–blue. During measurement, the resistance between each pair of these three wires should be measured separately.

Measure the resistance of the accelerating coil:

Set the multimeter to the resistance measurement range.
Connect the test fixture or probe to the white‑red and white‑blue wires, respectively.
Record the resistance value displayed on the multimeter, such as 69.3 Ω in the example.

Measure the resistance of the hold coil:

Connect the test fixture or probe to the red and blue wires, respectively.
Record the resistance value displayed on the multimeter, such as 277.9 Ω in the example.

Comparison with the standard value:

According to the “Brake Coil Resistance Standard” or the equipment manual, compare the measured values with the standard specifications. In general, a certain reasonable deviation is permissible; however, if the deviation exceeds an acceptable range, it may indicate a problem with the coil.
3. Precautions
When measuring resistance, ensure that the equipment is de-energized to prevent electric shock.
During measurement, ensure good contact to prevent poor contact from causing measurement errors.
If the measurement results differ significantly from the standard value, further inspection should be conducted to determine whether the coil is damaged or aged.
Evaluation of the Brake Coil Resistance
1. Resistance Value Assessment
If the resistance between any two of the three wires of the brake coil is zero or infinite, or deviates significantly from the standard value, it may indicate that the coil is damaged or that there is an open circuit, a short circuit, or other issues.
Under normal conditions, the resistance values of the acceleration coil and the holding coil should each be close to their respective standard values, and in combined measurements across different pairs of terminals, the resistance values should exhibit a reasonable series or parallel relationship.
2. Analysis of Influencing Factors
Input Voltage: The resistance of the brake coil may be affected by the input voltage. During measurement, ensure that the input voltage matches the value indicated on the equipment’s nameplate.
Ambient temperature: Excessively high or low ambient temperatures can also affect the resistance of the brake coil. Therefore, environmental factors should be taken into account during measurement, and appropriate measures should be implemented when necessary.
Wiring method: Incorrect wiring can lead to inaccurate resistance measurements. Therefore, before taking measurements, ensure that the wiring is performed correctly in accordance with the equipment’s schematic or manual.
3. Maintenance and Care
Regularly check the resistance of the brake coil to promptly identify and address potential issues.
Keep the equipment’s operating environment clean and dry to prevent dust, moisture, and other contaminants from damaging the brake coil.
During equipment shutdowns or maintenance, perform the necessary inspections and maintenance on the brake coils to ensure they remain in good working condition.
Conclusion

Measuring and evaluating the resistance of brake coils is a critical step in the maintenance of SEW motor brakes. By employing proper measurement techniques and scientifically sound evaluation criteria, potential issues with the brake coils can be identified promptly, ensuring stable equipment operation and reliable braking performance. In practice, safety regulations must be strictly observed to guarantee the accuracy and reliability of measurement results.