UPS battery overview - SCU

UPS battery overview

VRLA batteries are sealed, usually with in polypropylene plastic, the advantage being that there is no liquid sloshing around that might leak or drip.

It’s a well-known fact that the battery is the most vulnerable part of the modular uninterruptible power supply. In fact, battery failure is a leading cause of load loss. Understanding how to properly maintain and manage UPS batteries can not only extend battery service life, but can also help prevent costly downtime.

The most common type of battery used in UPSs is valve-regulated lead acid (VRLA) batteries, also known as sealed or maintenance free. VRLA batteries are sealed, usually within polypropylene plastic, which offers the advantage of not containing any sloshing liquid that might leak or drip. Because water cannot be added to VRLA batteries, recombination of water is critical to their life and health, and any factor that increases the rate of evaporation or water loss — such as temperature or heat from the charging current — reduces the life of the battery

Frequently asked questions:

1. What is the “end of useful life”?

The IEEE defines end of useful life for a UPS with li-ion battery as being the point when it can no longer supply 80 per cent of its rated capacity in ampere-hours. When your battery reaches 80 per cent of its rated capacity, the ageing process accelerates and the battery should be replaced .

2. Is there any difference between the batteries used by smaller UPSs, from 250 VA to 1 kVA, and the ones used by larger UPSs?

While basic battery technology, and the risks to battery life, remains the same regardless of UPS size, there are some inherent differences between large and small applications. First, smaller UPSs typically have only one VRLA battery that supports the load and needs maintenance. As systems get larger, increasing battery capacity to support the load gets more complicated. Larger systems may require multiple strings of batteries, introducing complexity to battery maintenance and support. Individual batteries must be monitored to prevent a single bad battery from taking down an entire string, thereby putting the load at risk. Also, as systems get larger, wet-cell batteries become much more common.

3. My UPS has been in storage for over a year. Are the batteries still good?

As batteries sit unused, with no charging regimen, their life will decrease. Due to the self-discharge characteristics of lead acid batteries, it is imperative that they be charged after every six to 10 months of storage. Otherwise, permanent loss of capacity will occur between 18 and 30 months. To prolong shelf life without charging, store batteries at 10°C (50°F) or less.

4. How is battery run time affected if I reduce the load on the UPS?

The battery run time will increase if the load is reduced. As a general rule, if you reduce the load by half, you triple the run time.

5. If I add more batteries to a UPS can I add more load?

Adding more batteries to a UPS can increase the battery run time to support the load. However, adding more batteries to the UPS does not increase its capacity. Ensure that your UPS has sufficient capacity to support your load, then add batteries to fit your run time needs.

6. What is the average lifespan of UPS batteries?

The standard lifespan for VRLA batteries is three to five years. However, expected life can vary greatly due to environmental conditions, number of discharge cycles, and adequate maintenance. Have a regular schedule of battery maintenance and monitoring to ensure you know when your batteries are reaching their end of useful life.

7. How can you be sure UPS batteries are in good condition and ensure they have maximum holdover in the event of a power failure? What preventive maintenance procedures should be done and how often?

The batteries used in the UPS and associated battery modules and cabinets are sealed, valve-regulated lead acid battery often referred to as maintenance-free batteries. While this type of battery is sealed and you do not need to check the fluid level in the battery, they do require some attention to ensure proper operation. SCU’s BMS technology extends the life of valve-regulated lead acid batteries by applying sophisticated logic to the charging regime. BMS also provides an additional feature for monitoring battery condition and advance warning about the end of battery life upon detection of a weak battery.

8. How long does it take for the UPS batteries to recharge?

On average, it takes 10 times the discharge time for the UPS batteries to recover. (A 30-minute battery discharge requires about 300 minutes to recharge.) After each power outage, the recharge process begins immediately. It is important to note that the load is fully protected while the batteries are recharging. However, if the batteries are needed during the recharge time, the holdover time available will be less than it would have been if the batteries were fully charged.

9. What are the risks associated with a lack of battery maintenance?

The primary risks of improperly maintained batteries are load loss, fire, property damage and personal injury.

10. What is thermal runaway?

Thermal runaway occurs when the heat generated in a lead acid cell exceeds its ability to dissipate that heat, which can lead to an explosion, especially in sealed cells. The heat generated in the cell may occur without any warning signs and may be caused by overcharging, excessive charging, internal physical damage, internal short circuit or a hot environment.

11. Why do batteries fail?

Batteries can fail for a multitude of reasons, but common reasons are:

• high or uneven temperatures

• inaccurate float charge voltage

• loose inter-cell links or connections

• loss of electrolyte due to drying out or damage to the case

• lack of maintenance, aging

12. How is battery performance generally measured?

Batteries are generally rated for 100+ discharges and recharges, but many batteries show a marked decline in charging capacity after as few as 10 discharges. The lower the charge the battery can accept, the less run time it can deliver. Look for batteries with a high-rate design that sustains stable performance for a long service term.

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