To ensure the integrity of any Uninterruptible Power Supply, Telecommunications 48V system or generator, the batteries must be checked and maintained.
Surprisingly, whatever the cost of your Power Protection system, whether it is a stand-alone UPS System or Standby Diesel Generators, the most common single point of failure is the batteries.
High resistance, leakage or open circuits will cause batteries to fail, no longer providing the expected autonomy or, in the case of a generator, the inability to start. The result – loss of the site load, and suddenly you require a 24-7 emergency call-out engineer.
Uninterruptible power supplies may have internal batteries or batteries housed in separate cabinets. Each battery has a recommended design life, usually 5 years or 10 years, although these figures are optimistic as they are based on in-lab tests under ideal situations and don’t take into account the high usage of the UPS battery system caused by intermittent spikes, brown outs or voltage fluctuations, which are absorbed by the batteries to protect your mission critical sensitive systems.
Even though the battery may have an operating life expectancy stated by the manufacturer of typically up to ten years, if it is not checked on a regular basis it can, and will, fail. All it takes in a string of 32 block is for one battery to develop high impedance and then complete string will be useless, as the load will be unable to draw the current it requires, and as a result the load will be lost and your critical load will fall over. The old batteries can be removed and new batteries supplied.
Split casing is the most obvious sign of battery leakage, caused by a failure within the sealed lead acid battery. Other issues of high impedance and open circuit are not so obvious and require regular checks.
There are a number of different types of battery construction but they can be loosely divided into to two common types- ‘wet cells’ and ‘valve regulated lead acid’ (VRLA) batteries (often referred to as just ‘sealed lead acid batteries’).
Wet cell battery maintenance can be more time consuming, as the trade off against increased life expectancy is the higher cost of maintenance due to the necessity of taking specific gravity readings and ‘topping’ up the cell. A visual check of wet cell batteries needs to be undertaken on a more regular basis as any noticeable drop in electrolyte level must be swiftly rectified.
The VRLA ‘lead acid’ battery is more difficult to check, being a sealed battery. The most common method of testing, often built into most UPS systems’ equipment, is a battery self-test, which is often carried out automatically on a weekly / monthly time cycle. If the test fails then the UPS system will generate an alarm. The major drawback is if the equipment is supporting a small load comparative to the capacity of the equipment, and therefore the battery will not be worked very hard and could prematurely fail.
The more reliable method for regularly testing a battery is either:-
1. By loading the battery to one third of its capacity and carrying out a capacity test
2. Impedance testing -increasingly popular as it’s non-intrusive.
There are several methods of achieving the same result, but one method is to pass a known AC current through the battery and measure the AC voltage and thus, by using Ohms Law, calculate the battery impedance. These results can be compared with the manufacturer’s recommended value, and by keeping records can be compared over a period of time, allowing a replacement programme to be implemented when the battery impedance has reached a preset value.
Whichever method of battery testing you choose, regular battery maintenance is an integral part of any Uninterruptible Power Supply or Generator standby power protection system .
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