Quick Answer
A BLDC motor with an electromagnetic brake provides an additional level of protection when electrical power is interrupted, because the brake can automatically engage when its release power is removed, helping prevent the motor shaft and connected load from rotating unintentionally.
Unlike a standard BLDC motor, which may lose its ability to generate controlled driving torque when the power supply or motor controller fails, a brake-equipped BLDC motor can provide a mechanical holding function even when the motor is not energized, provided that the brake is correctly designed and installed.
This configuration is particularly important for applications involving vertical movement, suspended loads, lifting equipment, automated doors, medical beds, stairlifts, AGVs, and industrial machinery, where unexpected movement after a power failure can damage equipment or create safety risks.
Key takeaway: A BLDC motor provides controlled motion, while an electromagnetic holding brake helps maintain the load position when electrical power is unavailable. Together, they provide a more reliable motion-control solution for applications requiring controlled stopping and power failure protection.
What Happens When a BLDC Motor Loses Power?
A Brushless DC motor relies on an electronic driver to control current switching in the stator windings, allowing the permanent-magnet rotor to produce controlled rotation.
During normal operation, the motor controller regulates speed, torque, acceleration, and deceleration according to the application requirements.
However, when the main power supply suddenly fails, several problems can occur:
– The motor controller stops supplying controlled phase current.
– Electromagnetic driving torque is no longer available.
– The rotor may continue rotating because of inertia.
– An external load may drive the motor shaft.
– A vertical or suspended load may move downward under gravity.
– The equipment may lose its ability to maintain a defined position.
For example, consider an electric lifting mechanism using a BLDC motor to raise a 100 kg load. If the power supply suddenly disappears while the load is elevated, the motor may no longer provide the torque required to hold its position.
A mechanical brake provides an additional holding mechanism to reduce this risk.
How Does an Electromagnetic Brake Work?
An electromagnetic brake commonly used with BLDC motors is a spring-applied, electrically released brake.
Its operating principle is relatively straightforward.
Normal Operation: Brake Released
When the brake receives its specified DC release voltage, an electromagnetic coil generates magnetic force that overcomes the spring force and releases the friction surfaces.
The motor shaft can then rotate normally.
Power Failure: Brake Engaged
When the brake release power is interrupted, the electromagnetic force disappears, allowing the internal springs to push the friction surfaces together.
The resulting friction generates braking torque and helps prevent unwanted shaft rotation.
Power Restoration: Brake Released Again
Once the power supply returns and the brake receives the required release voltage, the brake can disengage and the motor can resume operation according to the control system.
Why Are BLDC Motors with Brakes Important for Power Failure Protection?
A brake-equipped BLDC motor offers several engineering advantages, especially in equipment where maintaining load position is more important than simply stopping motor rotation.
Preventing Uncontrolled Load Movement
In vertical applications, gravity continues acting on the load even after the motor loses electrical power.
Without a mechanical holding brake, a lifting mechanism may move downward, depending on the transmission design, friction, and external load conditions.
An electromagnetic brake provides a mechanical holding force that helps maintain the load position after power interruption.
Typical applications include:
– Electric lifting systems
– Stairlift mechanisms
– Rehabilitation beds
– Hospital equipment
– Automated lifting platforms
– Industrial positioning systems
Maintaining Position During Power Interruptions
Precision equipment often needs to maintain its position when the power supply is interrupted.
For example, a medical bed or automated positioning system may need to prevent an adjustable platform from moving unexpectedly while an operator is working on the equipment.
A BLDC motor with a normally engaged electromagnetic brake provides a practical way to maintain mechanical position without continuously energizing the motor windings.
Reducing Dependence on Continuous Motor Current
A standard BLDC motor may require continuous current and active control to generate holding torque.
A spring-applied electromagnetic brake, however, can maintain its holding function mechanically without continuous electrical power to the brake release coil.
This can reduce the need for continuous motor energization when the equipment remains stationary for extended periods.
BLDC Motor with Brake vs. Standard BLDC Motor
| Performance Factor | Standard BLDC Motor | BLDC Motor with Brake |
|---|---|---|
| Speed control | Yes, with suitable driver | Yes, with suitable driver |
| Torque control | Yes, with suitable driver | Yes, with suitable driver |
| Mechanical holding | Depends on system design | Supported by integrated brake |
| Power failure protection | Limited | Improved |
| Vertical load applications | Requires additional holding solution | Suitable when correctly specified |
| Position maintenance | May require continuous motor torque | Mechanical holding capability |
| System complexity | Lower | Higher |
| Component cost | Generally lower | Generally higher |
Important: An electromagnetic holding brake is not automatically a complete safety system. Its holding torque, response time, stopping energy, wear characteristics, and failure modes must be evaluated according to the application.
How to Select the Right BLDC Motor with Brake?
Selecting a brake-equipped BLDC motor requires more than matching rated motor power. Engineers must evaluate the motor, brake, transmission, load, and control system together.
Step 1: Calculate the Required Holding Torque
Determine the maximum external torque acting on the motor shaft when the equipment is stationary.
For vertical lifting equipment, this includes the load weight, transmission ratio, mechanical efficiency, and the geometry of the lifting mechanism.
The selected brake must provide sufficient holding torque with an appropriate engineering safety margin.
For preliminary evaluation, engineers may investigate a holding-torque margin of 1.5–2.0 times the calculated static requirement, but this is only an illustrative design starting point, not a universal safety requirement.
Step 2: Confirm Brake Voltage
Common electromagnetic brake configurations use DC release voltages such as:
– 12 VDC
– 24 VDC
– 48 VDC
The actual voltage must match the brake coil specification, available power supply, and control circuit.
A 24V BLDC motor does not automatically require a 24V brake; the motor and brake electrical ratings must be checked independently.
Step 3: Evaluate Motor Speed and Torque
The motor must meet the application’s operating requirements, including:
– Rated voltage
– Rated speed
– Continuous torque
– Peak torque
– Acceleration requirements
– Duty cycle
– Thermal performance
For example, a lifting system operating at low speed may require a motor with a suitable gearbox to provide the necessary output torque and speed.
Step 4: Check Brake Engagement and Release Timing
Brake timing is critical.
During startup, the brake should release before the motor applies significant driving torque. During stopping, the motor should normally decelerate the load under controlled conditions before the brake engages.
The exact sequence depends on the motor controller, brake characteristics, and application safety requirements.
Step 5: Validate the Complete System
Before mass production, engineers should verify:
– Static holding torque
– Dynamic stopping performance
– Brake engagement time
– Brake release time
– Repeated stopping performance
– Temperature rise
– Mechanical wear
– Power interruption behavior
Common Applications of BLDC Motors with Brakes
Stairlift Systems
A brake-equipped BLDC motor helps prevent uncontrolled movement when the lifting mechanism stops or loses power, supporting safer passenger transportation.
Medical and Rehabilitation Beds
The brake helps maintain the selected bed position and reduces the risk of unintended movement during power interruptions.
Industrial Lifting Equipment
Mechanical holding capability is important when handling suspended loads or operating vertical positioning mechanisms.
AGVs and Automated Equipment
A brake can help hold the vehicle or mechanism stationary when required, although stopping distance and vehicle-level safety functions must also be considered.
Common Problems with BLDC Motor Brakes
| Problem | Possible Cause | Recommended Check |
|---|---|---|
| Brake does not release | Incorrect voltage or wiring | Check brake coil voltage and connections |
| Motor cannot start | Brake remains engaged | Verify brake release sequence |
| Load slips after stopping | Insufficient holding torque | Recalculate maximum load torque |
| Brake overheats | Incorrect voltage or excessive duty | Check coil rating and operating cycle |
| Motor experiences sudden shock | Incorrect brake timing | Adjust motor and brake sequencing |
| Excessive brake wear | Frequent dynamic stopping | Review stopping frequency and brake energy rating |
| Motor moves after power failure | Brake wiring or mechanical failure | Test fail-safe engagement and mechanical condition |
Common Engineering Mistakes
1. Using motor torque as the brake holding-torque specification
Motor rated torque and brake holding torque are different parameters. The brake must be selected according to the external load and mechanical transmission.
2. Ignoring gearbox efficiency
A gearbox changes the torque and speed seen at the output shaft. Engineers must calculate the brake requirement at the actual brake installation position.
3. Treating a holding brake as a dynamic braking solution
Many spring-applied electromagnetic brakes are primarily designed for static holding rather than repeated high-energy emergency stopping. Dynamic braking capability must be confirmed with the manufacturer.
4. Ignoring brake timing
If the brake engages while the motor is still producing substantial torque, mechanical shock, noise, and premature wear may occur.
Why Choose UNITED MOTION INC. for BLDC Motor Solutions?
Selecting a BLDC motor for an OEM project involves more than choosing rated power and speed. The motor must work with the mechanical transmission, brake, feedback components, and control system to meet the application’s actual operating conditions.
UNITED MOTION INC. provides BLDC motor solutions across approximately Φ28–Φ110 mm frame sizes, with configurable options such as:
– Customized voltage, speed, and torque
– Gearbox integration
– Encoder integration
– Integrated motor drivers
– Application-specific motor configurations
– OEM motor customization
For projects requiring power failure protection, engineers should also evaluate electromagnetic brake integration according to the required holding torque, brake voltage, mounting dimensions, and control sequence.
Whether the application involves stairlifts, rehabilitation beds, industrial automation, lifting equipment, or AGVs, UNITED MOTION INC. supports OEM customers in developing motor configurations based on their application requirements.
Final Engineering Recommendations
A BLDC motor with an electromagnetic brake is a practical solution for applications where unexpected movement after power interruption must be controlled.
However, reliable protection depends on selecting the correct brake holding torque, matching the electrical specifications, coordinating motor and brake timing, and validating the complete mechanical system under actual operating conditions.
For OEM manufacturers, the most effective approach is to treat the motor, brake, gearbox, encoder, and driver as one integrated motion-control system rather than selecting each component independently.
FAQ: BLDC Motors with Electromagnetic Brakes
1. What happens when a BLDC motor loses power?
When the power supply fails, the motor controller generally stops providing controlled driving torque. If the motor is equipped with a correctly configured spring-applied electromagnetic brake, the brake engages when its release power is removed, helping prevent unwanted shaft rotation.
2. Why does a BLDC motor need an electromagnetic brake?
An electromagnetic brake provides mechanical holding capability when the motor is stopped or loses electrical power. It is particularly useful for vertical lifting systems, stairlifts, medical beds, and industrial positioning equipment.
3. Is an electromagnetic brake normally engaged or released?
A common fail-safe design is spring-applied and electrically released. The brake remains engaged without release power and disengages when the specified electrical voltage is supplied.
4. Can a BLDC motor brake hold a vertical load?
Yes, provided the brake has sufficient rated holding torque and is correctly integrated with the transmission and mechanical structure. Engineers must also consider load variations, safety factors, brake wear, and applicable safety requirements.
5. What voltage is required for a BLDC motor brake?
Common DC brake voltage options include 12V, 24V, and 48V, although actual specifications vary by manufacturer and brake model. The brake voltage should be verified independently of the motor’s rated voltage.
6. Can a gearbox be combined with a BLDC motor brake?
Yes. A BLDC motor can be configured with a gearbox and electromagnetic brake to provide the required output speed, torque, and holding capability. Brake positioning and holding-torque calculations must account for the transmission arrangement.