Will your vfd stand the test of time?

Whenever you buy a piece of equipment for your facility, you want to know what you’re getting for your money. Variable frequency drives (VFDs) are a crucial part of many systems because of their ability to control speed and save energy. Still, many people don’t know how they work internally and how long they should last.  

From our experience, most low voltage VFDs will last about ten years, whereas medium voltage VFDs will often last 20. This can vary and is based on many factors.  

There are some key things to remember when discussing VFD lifespans. We’ll talk through what components will fail most often, why they fail, how to extend their life, and when to start planning for a replacement.  

VFD lifespans are based on components

Very rarely does an entire VFD fail at once. A lightning strike or surge may damage multiple components, or dropping a VFD in a lake may cause overall damage. In most cases, however, you’re much more likely to see individual components fail that take the VFD out of service.

Fans tend to fail because they are a moving component that's most likely to encounter contamination. Cooling fans move air over heat sinks and often encounter dust or debris.  

Mitsubishi boasts about extended fan lifespans in their newest F800 series VFDs. They say, “The service life of the cooling fans is now ten years.” That life can be much shorter based on the environment or how often you need fans for cooling. It also is based on the assumption that you're properly cleaning and caring for the fans and VFD.

There are ways to maximize the life of your VFD cooling fans.

Capacitor life can be extended when you reduce the temperature they are stored and operated at. You also need to ensure they are periodically used when in storage or in a less-active process.

Boards  

Circuit boards are used throughout VFDs for controlling functions. They are typically more reliable than fans or capacitors but can still be susceptible to failure. Circuit boards will often last the life of the VFD if it operates in a good environment.

Suppose the environment is dirty, dusty, wet, or has corrosive gases and materials. In that case, the boards will often be the first to fail. We’ve also seen failures from mice, snakes, and other animals entering the electrical equipment to seek warmth and leaving a mess on boards.  

Extend the life of circuit boards by keeping the VFD and environment clean, cool, dry, and limiting access to the internal components of the VFD.  Keeping a VFD in an appropriate enclosed panel can help to avoid many of these issues.

We’ve seen that a VFD retrofit is often a good step before gutting the whole system to gain reliability for a lower cost. Rather than replacing switchgear, wiring, conduit, and many other components, replacing just the VFD or the VFD panel can give you another 10 to 20 years of reliable service for a reduced spend on your operation budget.  

You will want to start looking at a retrofit replacement when the repair cost approaches 50% of the price of a replacement VFD. You also will want to evaluate it if you see repeated part failures that require repairs or if it is a critical application that needs higher reliability.

You can also plan proactive retrofits. As your low voltage system nears ten years of age, you can evaluate whether the components are still testing strong. You can also examine whether the technology still integrates well with your building management system (BMS) and the rest of your system. There are often enough benefits to upgrading equipment to determine whether that’s a good path for you.