Hey there! I'm a supplier of 18.5KW VFDs, and today I wanna chat about the types of braking resistors that are suitable for these 18.5KW VFDs. First off, let's understand why braking resistors are important for VFDs.
When a VFD is used to control an electric motor, during deceleration or when the motor acts as a generator (like in a downhill - moving conveyor belt situation), the energy generated by the motor needs to be dissipated. That's where braking resistors come in. They absorb and convert this excess electrical energy into heat, preventing over - voltage in the VFD and ensuring stable operation.
Types of Braking Resistors
Wire - Wound Braking Resistors
Wire - wound braking resistors are a popular choice. They're made by winding a resistive wire around an insulating core. The wire is usually made of materials like nichrome or kanthal, which have high resistivity and good heat - resistance properties.
One of the big advantages of wire - wound resistors is their high power - handling capacity. For an 18.5KW VFD, you need a resistor that can handle a decent amount of power, and wire - wound resistors fit the bill. They can dissipate large amounts of energy quickly, which is crucial when the motor is generating a lot of power during deceleration.
Another plus is their reliability. The construction of wire - wound resistors is relatively simple, and they can withstand high temperatures without significant changes in their resistance value. This means they'll work consistently over time, which is super important for industrial applications where the 18.5KW VFD might be running for long hours.
However, they do have a few drawbacks. They're relatively bulky compared to some other types of resistors. If space is a constraint in your installation, this could be an issue. Also, they can be a bit more expensive than some other options, but considering their performance and reliability, the cost might be worth it.
Aluminum - Clad Braking Resistors
Aluminum - clad braking resistors are another option to consider. These resistors have a resistive element that's enclosed in an aluminum housing. The aluminum housing serves multiple purposes. It provides mechanical protection to the resistive element, and it also helps with heat dissipation.
The heat - dissipation property is a key advantage. The aluminum acts as a heat sink, transferring the heat generated by the resistive element to the surrounding air more efficiently. This means that for an 18.5KW VFD, an aluminum - clad resistor can operate at a lower temperature compared to a wire - wound resistor of the same power rating, which can extend its lifespan.
They're also more compact than wire - wound resistors. This makes them a great choice if you're working in a tight space. You can easily install them in a control panel without taking up too much room.
On the downside, their power - handling capacity might be a bit lower compared to wire - wound resistors. If your application involves very rapid deceleration or high - energy braking events, an aluminum - clad resistor might not be able to handle the load as well as a wire - wound one.
Cement - Encased Braking Resistors
Cement - encased braking resistors are a cost - effective option. They consist of a resistive element that's embedded in a cement - like material. The cement provides insulation and protection to the resistive element.
These resistors are quite durable. The cement casing helps to protect the resistive element from mechanical damage and environmental factors like dust and moisture. This makes them suitable for harsh industrial environments where the 18.5KW VFD might be exposed to tough conditions.
They're also relatively inexpensive, which is a big plus if you're on a tight budget. However, their power - dissipation capabilities are limited compared to wire - wound resistors. They're better suited for applications where the braking energy is relatively low and the deceleration is not too rapid.
Factors to Consider When Choosing a Braking Resistor for an 18.5KW VFD
Power Rating
The power rating of the braking resistor is crucial. You need to choose a resistor that can handle the power generated by the motor during braking. A general rule of thumb is to select a resistor with a power rating that's at least 1.5 to 2 times the continuous power rating of the VFD. For an 18.5KW VFD, a braking resistor with a power rating of around 27.75KW to 37KW would be a good starting point.
Resistance Value
The resistance value of the braking resistor affects the braking torque and the rate of energy dissipation. A lower resistance value will result in higher braking torque but also higher power dissipation. You need to find the right balance based on your specific application. You can consult the VFD's manual or a technical expert to determine the optimal resistance value for your 18.5KW VFD.
Duty Cycle
The duty cycle refers to the ratio of the time the resistor is in use to the total time. If your application involves frequent and rapid braking, you'll need a resistor with a high - duty - cycle rating. For example, in a conveyor system that stops and starts frequently, the braking resistor will be working more often, so you need a resistor that can handle this continuous operation.
Other Related VFD Products
If you're interested in other VFD products, we also offer 5.5KW VFD, which is suitable for smaller - scale applications. And if you have single - phase motors, our Single Phase Motor VFD Drive is a great option. For larger industrial setups, we have Three Phase VFD available.
Wrapping Up
Choosing the right braking resistor for your 18.5KW VFD is essential for the proper and efficient operation of your motor control system. Whether you go for wire - wound, aluminum - clad, or cement - encased resistors, make sure to consider factors like power rating, resistance value, and duty cycle.
If you're in the market for an 18.5KW VFD or need help selecting the right braking resistor, I'd love to have a chat with you. Reach out to me for a detailed discussion about your requirements and let's find the best solution for your application.
References
- Electrical Engineering textbooks on Variable Frequency Drives and Braking Resistors
- Manufacturer's manuals for 18.5KW VFDs and braking resistors