Keeping a Spare VFD
Many applications that utilize a variable frequency drive (VFD) are critical and can’t afford to have extensive downtime. One option that many opt for is to keep a spare VFD on the shelf, ready to switch out if the need arises. If you are not careful, however, that VFD may not be ready to use when you need it. Below are several things to look for to make sure your spare VFD is ready to pull from long term storage and put right in to service.
One of the easiest issues to address is where and how you are storing the VFD. Make sure that it is cool, clean, and dry. Common issues we see are that the warehouse where a spare VFD is stored has excessive moisture, dust, or even animal problems. The number of issues we have seen when mice or other animals decide to make nests in VFDs is higher than most people realize, and dust and water always present a problem.
Another issue to monitor is temperature. Most inverters are rated to run at temperature similar to 0-40°C. VFDs can be stored at slightly more extreme temperatures than they can be run at, but make sure to consult the manual for your VFDs to find what conditions are recommended.
Maintenance of Capacitors
Electrolytic capacitors are used in almost all low voltage drives, and some medium voltage as well. These capacitors are filled with an electrolytic gel which give them their name. As these capacitors sit without being used, the gel starts to dry up and cause issues. Some medium voltage VFDs use dry film capacitors which do not encounter these problems, so a crucial aspect of servicing your drives is to identify what type of components are inside.
One of the best things you can do for your VFD is to energize it yearly. When you perform the annual preventative maintenance on your other drives, find a way to energize the stored VFD. If electrolytic capacitors sit for more than a year without being energized, you need to make sure to reform the capacitors before putting it in to service, which takes valuable time at what could be a moment when your process is down. Most electrolytic capacitors only have a 5-7 year shelf life, so if you go too long without energizing or reforming capacitors, you may find it is too late to save the VFD without performing actual repairs.
One issue with just reforming capacitors on VFDs is that you can only reform the DC bus capacitors, and capacitors that are on the printed circuit boards are not reformed. That is why the best recommendation is to actually go a step past energizing stored VFDs every year and to actually rotate out equipment at every annual preventative maintenance service to keep all VFDs in their best running shape.
Although the issues listed above address the biggest issues that come from storing VFDs long term, it is best to have an experienced technician look over VFDs and make sure they don’t see any other obvious problems. It is possible to find instances where parts are taken off of a stored VFD to fix one in service. You might also find damage from other activities in the warehouse, such as equipment getting bumped by forklifts or other equipment. Getting someone who is experienced with VFDs and can identify issues like these will go a long way toward keeping your VFDs ready to go when you need them.
We Can Help!
Whether you’re looking at getting a VFD for service, sourcing a spare VFD, or want to explore service on your stored equipment, we can help you make sure your site stays up and running.