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As we have discussed in a previous blog, there are several popular UPS topologies (designs) to choose from when seeking power protection for your facility. Each UPS design has its benefits and drawbacks. The standby UPS design is low cost, but it can result in disruption of operation of sensitive loads. The line-interactive UPS provides a more comprehensive level of protection from power anomalies (thanks to power conditioning), but it still has a transfer time to batteries in the case of an outage or disruption.  Finally, the double-conversion (online) UPS design provides top level protection and efficiency, but it comes with a high price tag.

While an understanding of each UPS topology is important, it is equally important to have some understanding of components which make up the UPS. This blog will cover the main functional components found in UPSs: batteries, inverter, rectifier and static bypass.


Batteries are the heart of every UPS. Additionally, batteries are the main source of UPS failure because they are the most likely component to fail. Batteries die for a variety of reasons – high or uneven temperatures, lack of maintenance, aging – and each battery type has its own recommendations for proper care.

The most common types of UPS battery are: Valve Regulated Lead Acid (VRLA), Flooded Wet Cell (also known as VLA) and Lithium-Ion. VRLA has long been the most popular UPS battery type, because it is readily available and therefore relatively inexpensive. VRLA UPS batteries generally last 3-7 years in the proper environment. VLA batteries can provide a longer lifespan – as much as 20 years – but they require more maintenance when compared to their VRLA counterparts. Lithium UPS batteries are the “new kid on the block,” and are just gaining popularity in the UPS battery market. UPSs built specifically to use lithium ion battery technology are in the market today. 

No matter what battery type is used in your UPS, it is important to keep your UPS and its batteries in a viable environment to ensure longevity. UPS batteries should be maintained along with other components, and they should be replaced on a strict schedule to ensure that battery failure does not result in down time for your facility.


The inverter, found in all UPS designs, converts DC power from batteries (or from the rectifier) back into AC power for load use. In double conversion UPS designs, during normal operation, the rectifier and inverter are used in tandem to convert AC to DC and DC to AC (i.e. double conversion) which protects IT loads from any power anomalies. In standby and line interactive UPS designs, the inverter is switched on immediately after utility power goes down, to deliver battery power to the load. The downside to these designs is the “transfer time” to batteries – meaning it takes time (milliseconds) for the UPS to switch from normal operation over to the inverter/batteries.


The rectifier, in double conversion UPS designs, coverts utility AC power in to DC power. The rectifier, coupled with the inverter, allows for protection from power anomalies and delivers clean power to the load. Standby and line-interactive UPSs will not contain a rectifier. This is because these designs deliver utility power to the load during normal operation. These designs will have a battery charger which allows the batteries to remain ready in case of power disruption.  

Static Bypass

The static bypass switch allows utility AC power to flow directly through the UPS to the load, bypassing UPS components. Static bypass is a feature of double conversion UPS systems. When major preventive maintenance is needed on a UPS, normal operation will be halted, and a technician will switch the UPS into bypass (maintenance) mode. In this state, the load is vulnerable to a utility outage.

With more than 35 years of field experience and leadership in power protection, SEPS is well qualified to perform UPS preventive maintenance. SEPS offers a full suite of UPS services and all technicians are trained and certified to manufacturer standards, assuring a thorough job.  For more information, please contact us, or speak with one of our Power Protection experts at 630-283-2399 or

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