Selecting the right variable frequency drive (VFD) is essential to the proper operation of your equipment. By using these efficient systems, you can boost profit and productivity in your business – but only if you choose the right one. With that in mind, here are 6 important points to help guide you through the decision-making process, so you can make the best VFD investment for your company.
Determine the Size You Need
Choosing the size of your VFD can be complex. It’s tempting to make decisions based on horsepower ratings, however you should be thinking about the size of the VFD in the context of the motor’s maximum requirements and torque demand instead. Consider both the peak current and the torque, and aim for the best peak torrent in the worst operating conditions.
There will be a range of other elements that might contribute to sizing your VFD, including the operating profile of your chosen load, as well as the kind of load you’ll be using (variable or constant). Remember that altitude can impact VFD sizing, because most machines are air-cooled and air thins out at higher altitudes.
In some cases, oversizing may be necessary to help you get the most out of your VFD. In certain applications, your VFD might need to manage temporary overload conditions and if that’s the case, you’ll need a VFD that can do more than what your motor asks for.
Consider Braking Requirements
A VFD can control the flow of energy in a motor by adjusting the frequency of output energy and switching off to allow the motor to cool down. If your motor manages high-inertia loads, then it’s fair to assume that deceleration time will be lengthened. In some situations this won’t be a problem, but if you need to be able to decelerate heavy loads quickly, you’ll need to invest in a dynamic brake.
When motors begin to slow down, they can generate additional frequencies. Sometimes dynamic braking might allow for your VFD to stop the motor faster to enhance control over the motor. This is ideal for organizations that use frequent starting and stopping cycles.
Know Your Control Method
Control methods are pivotal to choosing the right VFD. In most cases, the control mode you choose will depend on what you’re using your motor for. There are three common forms of control mode: the closed-loop system, the open-loop vector, and volts-per-hertz (V/Hz).
Closed loop systems use encoder feedback, while sensor-free vectors don’t need to use encoder feedback to control speed. Typically, V/Hz VFDs use the ratio between frequency and voltage to send operating torque into the motor. V/Hz systems are great for applications like pumps and fans, while closed-loop and sensor-free solutions may be more appropriate for applications that require higher levels of control.
Consider Your Load Type and Load Amps
To run your VFD effectively, you’ll need to consider whether your VFD needs a variable or constant torque drive. Most fans and pumps require variability, while some applications require a consistent level of torque regardless of speed, such as conveyors and punch presses.
You should also consider full load amp (FLA) ratings at this time. Most experts suggest giving yourself a bit of a buffer when matching the amp rating from your motor’s FLA to your VFD if you have a load that requires a significant amount of effort to start.
Select Voltage and Speed Range
You’ll need to match the voltage of your new VFD and motor to the amount of voltage that’s available to you on site. In some cases, if you don’t know your ideal voltage, you might need to turn to a specialist for help.
When considering voltage, also take the time to think about speed. Typically, a motor shouldn’t run at anything less than 20% of its preferred speed or it is more likely to overheat. You’ll also need to make sure that you don’t run your motor over 20% more than its speed rating, as this could lead to a loss of torque.
If your aim is to improve performance with your VFD, then you’ll need to think about minimizing harmonics. Any non-linear load can create harmonics and if they become too excessive, those harmonics can damage your equipment. Passive filters like chokes can help reduce your exposure to harmonics and protect your VFD from overvoltage caused by capacitor switching. Active filters, on the other hand, have dynamic braking circuits that manage deceleration patterns in the motor.
As VFD experts, the team at Sloan Electric can support you well beyond the selection process. Contact us today to learn more about our unique VFD services.