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Understanding Brake Control in a 3-Phase 575V Motor with VFD: Seeking Insights

Question:

I have come across a 3-phase 575V motor being controlled by a VFD (Variable Frequency Drive), presenting a significant learning opportunity. While examining the motor panel, I noticed two brass terminals next to the power terminals, sparking curiosity about their purpose. Could these terminals possibly be designated for braking functions? The VFD in use is a Power Flex ALB 25B-E1P7N104. If these terminals are indeed for braking, I am unsure of the necessary steps to take next. Should I rely on the VFD for brake control, or can the motor itself manage this function? I would greatly appreciate any insights or guidance on this matter as I strive to expand my knowledge in motor technology. Thank you in advance for your assistance!

Top Replies

Are you considering which terminals to use for your application? DC- and DC+ are essential for creating a common-bus setup with several drives. BR+ and BR- are designated for linking an external Dynamic Brake resistor. Is dynamic braking necessary for your load? It's crucial if you're experiencing bus overvoltage issues. It's likely required for high inertia loads that need controlled deceleration.

User joseph_e2 asked about which terminals to use. DC- and DC+ can be utilized to create a common-bus system with multiple drives, while BR+ and BR- are for connecting an external Dynamic Brake resistor. If your load requires dynamic braking, particularly if you are experiencing bus overvoltage faults or have a high inertia load that needs to be slowed down under power, then these terminals at the motor are relevant. Thank you for your response.

Priyank Tripathi expressed confusion about the two brass terminals next to the power terminals on the VFD Power Flex ALB 25B-E1P7N104 drive. These terminals could potentially be used for brake terminals. When a motor is stopped or slowed down, it acts as a generator, causing a spike in voltage that could lead to a drive fault. To prevent this, a braking resistor can be connected to dissipate excess power, a process known as 'dynamic braking'. The need for a braking resistor depends on various factors such as load inertia and duty cycle. Alternatively, if the terminals are on the panel, they may be for powering a mechanical brake that stops and holds the motor. This mechanical brake can be used in conjunction with the dynamic brake for optimal motor operation. It is important to identify the specific terminals to determine their function.

One possible issue could be a thermistor or a protective mechanism for the motor. It is recommended to locate a datasheet for the motor or trace the wires to determine their purpose. This will help in diagnosing and resolving the problem effectively.

Are you wondering where to connect the cable coming from the motor? To properly wire it, start by referring to the motor literature. Based on my experience with Nord, it is likely a thermal overload rather than a brake. In this situation, you would typically connect it to a digital input on the drive that is set to trigger a fault when it shuts off.

More Replies

When troubleshooting motor issues, it's important to consider the possibility of a thermistor or other protective component being the cause. Refer to the motor's datasheet or trace the wires to determine their function. Additionally, examining diagrams found on the panel cover may provide insight into whether a thermistor is being used.

When it comes to determining where to wire the cable, it is suggested to refer to the motor literature for guidance. It is likely that the cable is connected to a thermal overload rather than a brake. In this case, it is recommended to wire it back to a digital input on the drive to trigger a fault when it turns off. Thank you for your response, it is greatly appreciated.

Priyank Tripathi inquired about a diagram found on the panel cover, wondering if it is related to a thermistor. The diagram is actually for detecting thermal overload using a bimetallic thermostat, not a PTC thermistor. Nord catalog page 117 provides more information on this. During normal operation, there should be continuity (< 50 mΩ) between the two leads. If the motor overheats, the thermostat will bend and open the circuit, signaling to shut off the motor to prevent further damage. Nord drives typically come with a dedicated digital input for this purpose, unlike what is found in the PowerFlex literature. For the on/off function of the thermostat, the closest option in PowerFlex literature is configuring an input as 'SW Enable'. Alternatively, if a PLC is controlling the drive, wiring the thermostat to it for a stop command is possible. In a simple 3-wire start/stop circuit, wiring in series with the stop button is an option, but it may make troubleshooting more difficult as an overtemp is not easily distinguishable from a normal stop command.

To identify the manufacturer and model number of your motor, inspect the nameplate on the motor. Check for thermal overload terminals or a motor brake. If a brake is present at the end of the motor, it may require power to open when the motor is running. Contact the manufacturer to verify this information. I have observed both thermal overload and brake terminals installed on motors before. Reach out to me at james for further assistance.

Thermal protection is essential for equipment safety. Many users implement a method where an unused input is looped through as a Normally Closed (NC) connection to act as an emergency stop (estop). This setup ensures that if a motor overheats, it will automatically stop and prevent a restart until the circuit is closed again.

Frequently Asked Questions (FAQ)

FAQ: 1. What is the purpose of the two brass terminals next to the power terminals on a 3-phase 575V motor controlled by a VFD (Variable Frequency Drive)?

Answer: - The two brass terminals are likely designated for braking functions in the motor system.

FAQ: 2. How can I determine if the brass terminals are indeed for braking functions in a motor system?

Answer: - Check the motor's technical documentation or consult the VFD manual for information on the specific terminals and their functions.

FAQ: 3. When using a VFD like the Power Flex ALB 25B-E1P7N104, should brake control be managed by the VFD or the motor itself?

Answer: - In most cases, the brake control is handled by the VFD, which provides more precise control over braking functions.

FAQ: 4. What steps should be taken to set up brake control in a motor system with a VFD?

Answer: - Refer to the VFD manual for instructions on configuring brake control settings and connecting the braking components.

FAQ: 5. How can I expand my knowledge in motor technology related to brake control and VFDs?

Answer: - Engage in further research, training courses, or seek guidance from experienced professionals in the field for a deeper understanding of motor technology applications.

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