Is It Time To Replace Your Uninterruptible Power Supply Capacitors?

Most people know that batteries in uninterruptible power supply (UPS) systems must be replaced, but capacitors are also susceptible to failure. To optimise UPS operations, replacing capacitors is a functional solution. 

What is an uninterruptible power supply capacitor?

The UPS capacitor is a simple electrical device that stores and releases electrical energy. There are many types of capacitors, however they are often cased in aluminium or chromium-plated cylinders and have a pair of conducting surfaces separated by an insulated element, the dielectric medium. Depending on the voltage amount, they will vary in size from thumbnail to a cooldrink can. 

What is the function of a UPS capacitors? 

Capacitors found in uninterruptible power supply systems are responsible for smoothing and filtering voltage fluctuations. If there’s a change in voltage input, the UPS capacitor will dampen this voltage change by eliminating voltage peaks and filling in the valleys to level it out. 

What is the lifespan of a UPS capacitor?

As with UPS batteries, UPS capacitors will degrade over time, reducing the ability of the capacitors to perform their job. Experts in UPS solutions should perform annual inspections to optimise their functionality. They will also be able to give you some indication as to the lifespan of your UPS capacitors, and whether a partial or full replacement is necessary. However, it’s advisable to schedule a full replacement of UPS capacitors between 7 and 10 years. Don’t wait until the capacitors have reached the end of their rated service life, rather schedule a replacement ahead of time. Some of the newer UPS systems have oil-filled capacitors which are rated for the lifespan of the UPS.

What influences UPS capacitor longevity?

Although there is nothing to completely prevent the degradation of uninterruptible power supply capacitors, there are certain things that will shorten the capacitor longevity by pushing them beyond design thresholds. These include:

  • Excessive current: If the current exceeds the manufacturer’s rating and the capacitors are exposed to overcurrent consistently, then they can be destroyed. They can withstand short periods of ripple current if the capacitors don’t overheat. 
  • Over-working: Capacitors that have to filter an unusual amount of voltage noise or constant transients are overworked. This could result in them needing replacement sooner. 
  • Excessive heat: This will cause the solution found within the UPS capacitors to evaporate, resulting in unsafe pressure and failure. The excessive heat can be caused by exterior temperatures or interior temperatures – such as a clogged air filter preventing airflow. 

How many capacitors are found in a UPS? 

The number of capacitors found within an uninterruptible power supply system will vary depending on the kVA rating of the unit. For a 750 kVA three-phase UPS there will be multiple large value power capacitors, while the smaller UPS units will have smaller value capacitors that are mounted on printed circuit boards.

What are the risks of not replacing a UPS capacitor? 

The impact of capacitor failure on an uninterruptible power supply system will vary according to the UPS type and size. However, some of the risks of not replacing in time include:

  • Capacitor lifespan – In an uninterruptible power supply, the failure of one or two capacitors might not be evident, but the remaining capacitors will have to assume the workload which shortens their lifespan. 
  • Risks downstream – Often the capacitor failure in a UPS will prompt it to switch to bypass mode so that the power bypasses the UPS filtering electronics. The UPS will remain functional but the downstream equipment isn’t protected. 
  • Operational impact – As the capacitors are unable to perform effectively, the operating conditions are impacted resulting in excessive heat and current.

For optimum UPS operations, it’s best to keep the device within a clean, cool environment so that there is no impact on the lifespan of the capacitors. It’s important to consult with experts in UPS solutions on product care and maintenance so that you are getting the most out of your UPS device. 

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