How to Plan a VFD Retrofit

By Tyler Simmons on 30th Nov 2022

As electrical infrastructure begins to age, facilities often see more upkeep costs and downtime as a result. Full facility overhauls are a rare and extensive project taking years of planning. More often than that, we see retrofit projects, where only certain pieces of equipment are replaced in order to extend the life of the overall system. 

Retrofits are a great middle ground between complete replacements and doing nothing. They typically hit the operations expense budget instead of the capital expense budget, meaning they often are also much easier to get approval for. 

As variable frequency drive technology progresses, you may see that your next VFD retrofit doesn’t have the option of replacing “like-for-like” as the old VFD is no longer manufactured, out of stock, or an older technology. When you start to plan a VFD retrofit, what are the things you should consider? 

Electrical Capabilities

In order to make sure that a new VFD will effectively replace an old one, you need to make sure it is capable of performing electrically. Although there are some minor differences between manufacturers, we’ve seen that the majority of VFDs are capable of running most applications if they’re sized properly, and matching the existing brand isn’t typically critical. 

If you take time to look at the motor specifications, the application, and several other factors, you can size the new VFD to work well. You can learn more about how to size a VFD here

It is always best to size the new VFD as if the old one didn’t exist. Based on advances in technology or the old size groupings a manufacturer used to have, your VFD may be oversized or undersized. Motors are often replaced before a VFD as well, so the motor amps or requirements may have changed since the original VFD installation. If you base your new VFD on the electrical specifications of the old VFD, you may just be compounding any errors. 

Control Methods

VFD technology has made big steps in control methods in the last 10 years. Most VFDs come with the ability to speak the most common protocols natively or else have the ability to quickly add a communication card to do so. Manufacturers have added the ability for ethernet communications as the standard for most lines, and PLC, SCADA, and HMI abilities are almost universally available. 

Make sure to communicate the needed method or protocol to your supplier. From there, they can verify that everything is compatible and will be set properly to run smoothly. 

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Physical Space

Because of how complicated the electrical and control considerations can be, we often see facilities overlook one of the most fundamental aspects of replacing a VFD: Will the new VFD physically fit? While better technology typically means a smaller, more compact package, it’s not always the case. 

We’ve also seen that the configuration can vary between manufacturers or even between generations of the same brand of VFD. Some lines may have a shorter but wider package, while others tend to be tall and skinny. 

If you have concerns about space and are struggling to find a good option that will fit where the old one was, there are often still options. Could you place the VFD in a different location? Could it be placed outside in a protective enclosure?  

Reason for Failure

While many retrofits happen as the result of planning for the future, some retrofits happen because the current drive is failing or has failed. If that’s the case, why did that VFD fail? If your VFD lasted less than 5-10 years, what factors caused it to fail? Were there environmental conditions like humidity, dust, or heat? Was it not sized appropriately? Were there consistent power surges that harmed it? 

If your VFD lasted a long time and there were no identifiable issues, it’s likely fine to move forward. But if your VFD had a shorter life than you had expected, how can you prevent those same factors from harming the replacement VFD? 

Inspecting a VFD panel
Inspecting a VFD panel

Looking at the Whole System

A VFD retrofit is a perfect time to improve your entire electrical system. While you’re looking at running a motor, you could also look at saving money and adding efficiency. 

If your VFD has been installed for more than a couple of years, there’s a good chance that your electrical system has changed in some way over the life of the VFD. You might have added a generator, expanded the plant, or taken away some equipment. You may have even changed the motor that the VFD is going to be running. 

A new electrical system means there might be effects from the VFD that you now need to consider for the first time. Harmonics can cause damage to other equipment, including generator alternators. Your power factor might have changed, or your utility started implementing penalties. You might have new motors that don’t have shaft grounding rings or have a longer motor lead length

Even if you had these issues in the past, it’s possible that you didn’t safeguard against them originally. As you look to add a new VFD, it is often the best time to add protections for the issues listed above. Making changes one at a time later can make it difficult and often more expensive to address these issues. 

Not only is it the best time to add protection, but it’s often the best time to improve your system. There are many options for VFDs that can reduce harmonics, improve power factor, add redundancy or bypass, make controls easier, improve efficiency, or provide other benefits. Making these changes can help to save future headaches and increase production. 

It can be tempting to simply replace a VFD with the closest replacement, but you miss the opportunity to use your operational budget to improve your entire electrical system and facility process.

Let Us Help Plan Your Retrofit

A retrofit project can be complicated, with existing equipment, new technologies, and different timelines to work through. We’ve done hundreds of retrofits through the years and can help you to plan yours. Reach out if you have questions or want help to make sure your system gets back up and stays reliable for years to come. 


If you have questions and want to ensure your system gets back up and stays reliable for years to come.