Why Capacitors are Important for Your UPS Health

When it comes to backup emergency power, an uninterruptible power supply (UPS) is fast becoming a must-have solution to protect valuable data and equipment from power surges or dips. To maintain optimum UPS function at all times, you need to ensure your capacitors are working well. Here’s everything you need to know about UPS capacitor health. 

What is a capacitor?

This is an electrical device, consisting of a pair of conducting surfaces – electrodes or metallic plates – found within an aluminium or chrome-plated cylinder. Ranging in size, capacitors store and release electrical energy for various uses. In addition to the two conducting surfaces, UPS capacitors have a third element known as a dielectric medium which determines the overall capacitance – how much energy charged is stored or managed. 

  • What are the capacitor types?

There are three primary capacitor types outlined below:

  1. AC input capacitors – These form part of the UPS’s input filter or the power factor correction stage, and they smooth out input transients and reduce harmonic distortion. 
  1. AC output capacitors – These form part of the UPS’s output filter and connect to the critical load output, controlling the waveform of the UPS output voltage. 
  1. DC capacitors – These form part of the rectification system and energy storage, smoothing out any voltage fluctuations.  

How many capacitors are in a UPS?

The number of capacitors required by a UPS is determined by the size and type of the UPS device, as well as the amount of energy required – the kVA rating. To put this in perspective, a PC has around 50 capacitors, while a 750kVA three-phase UPS can have hundreds of capacitors. 

What impacts UPS capacitor health?

Capacitors work to ensure the UPS receives a stable supply of power in terms of voltage and frequency at all times. Here’s a look at UPS capacitors and what can impact their health. 

Just like batteries, capacitors are able to degrade over time as the material of capacitors – paper, aluminium foil and electrolytes – breaks down physically and chemically, thereby losing capacitance. Eventually, the capacitor is no longer able to do its job. 

  • How long do capacitors last?

A UPS capacitor will be given an estimated lifespan by the manufacturer, which could be around seven years – if used consistently all the time. However, in reality, capacitors could deliver for up to a decade if properly monitored and maintained. 

  • What impacts capacitor health?

The lifespan of capacitor depends on a number of factors that can impact capacitor health. These include: 

  • Current 

When capacitors are regularly exposed to over-current conditions, then they can degrade or even be destroyed. 

  • Excess work

When there’s an unusual amount of voltage noise or frequent transients, then the capacitors are more likely to fail quicker. 

  • Excess heat 

If there is excess heat inside the capacitor (a clogged air filter and lack of airflow) or from the outside of the capacitor (ambient temperature) the solution inside the capacitor will evaporate resulting in unsafe pressure leading to failures. 

  • Impact of failed capacitors on UPS health

If your UPS capacitors undergo the aforementioned stress, then the UPS functionality can be impaired. The failure of a single capacitor wouldn’t necessarily have as much of an impact on the UPS as the remaining capacitors could pick up the slack, but over time, this would cause strain on the capacitors and negatively impact the UPS performance. The position of the capacitor and number of capacitors working in series or parallel will also determine the UPS health. In a worst-case scenario, serious failure of the capacitors will cause the UPS to switch to bypass mode. While the UPS is still operational, it doesn’t protect the downstream load. 

How to extend a capacitor’s life

To ensure your capacitors are operating at their optimum, it’s important to monitor and maintain them while also monitoring and maintaining operating conditions. This includes:

By working with UPS experts, JUP Solutions, you’re able to prolong the life of both your capacitors and UPS equipment so that you’re getting the full value of the backup power system. This also ensures that your UPS is always working at its best, providing you with peace of mind in the case of a power outage. 

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