Part 6 – How to ensure your UPS batteries don’t fail

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Causes of Battery Overheating

Battery overheating can occur due to external factors and the heat generated by the batteries themselves. Discharging batteries absorb heat, while charging batteries release heat at a rate of 0.02 watts per Ah per 12V DC.

When installing battery blocks in racks, it is vital to maintain a minimum 10mm gap between them to prevent overheating and avoid situations like thermal runaway, where the battery produces oxygen/hydrogen gas or expands. Overheated batteries pose significant health and safety risks and cannot be salvaged.

If a single battery cell deteriorates, it may charge at a faster rate than others, leading to overheating as it tries to match the charge level of the remaining cells in its group. This creates hot spots. If the cell fails completely, the rest of the battery pack, now with one cell less, will overcharge again, resulting in further heat buildup and reducing the pack's lifespan.

Discharge Cycles

The frequency of discharge-recharge cycles significantly affects battery life. The amount of energy a battery releases during discharge has a notable impact on its longevity, primarily due to contact deterioration.

Constant discharging can result in premature battery failure. To prevent excessive discharge cycles, it is important to account for fluctuations in UPS activity by compensating for voltage swells and sags.

Different Battery Options

Two common types of lead-acid batteries are open vented and valve regulated lead-acid (VRLA) batteries. VRLA batteries, which have a built-in venting mechanism, have replaced the older open vented type and are widely used.

Other battery options include Nickel-Cadmium (Ni-Cad) batteries, which have a wider temperature range (-20°C to +40°C) and increased durability. However, they contain hazardous cadmium and require proper disposal, leading to higher initial costs and disposal fees. Additionally, there are gel (sealed) batteries, which are less cost-effective than VRLA batteries and are designed for use in low temperatures. Their average lifespan, particularly at around 20°C, is approximately four to five years.

Battery Configuration - Series and Parallel Strings

Individual batteries typically provide a limited amount of electricity, usually 12V, so they are grouped together to achieve the required power output. A single battery is called a block and consists of multiple cells. When these blocks are connected, they form a battery string.

A series battery string is created by connecting individual blocks end to end. The total voltage achieved is the sum of all the individual blocks. This voltage should match the DC voltage required by the UPS.

A parallel battery string is formed by connecting multiple series strings in parallel. It is crucial to ensure that each series string contains the same number of blocks.

For any questions please get in contact with us here at Cetronic Power Solutions