So, you’ve specified, chosen andinstalled the correct valve regulated sealed lead-acid (VRLA) battery for your alarm or security stand-by system. You’ve checked the system, it works perfectly and that’s it. Or so you thought. The fact is, even with maintenance-free batteries, there are other – very important – aspects to be considered.
To ensure system integrity, all batteries need to be checked at regular intervals. And checking may require handling – which means safe handling. Then there are the batteries you keep in stock. These need to be stored correctly and, when they eventually come to the end of their effective operational life, they must be disposed of safely – now a mandatory requirement. So, let us consider these points and their importance to you.
Before beginning any work, it is advisable to measure and record the ‘float’ charging voltage of the system with a digital volt meter (DVM). Always refer to manufacturers’ instructions if large variances are measured or you suspect a fault.
Disconnect the equipment or system from the AC mains supply and isolate the battery leads from the load and charging circuitry.
Check the physical condition of the battery for signs of swelling. This may suggest that the battery is being over-charged or has passed its operational service life.
Check for electrolyte leakage. VRLA batteries are designed to recombine internal gases during charge and will not, therefore, leak electrolyte under normal operating conditions. If signs of electrolyte spillage are detected, suspect possible over-charging or inspect the battery casing for signs of damage.
Check the battery voltage across the open terminals (OCV) with a DVM or similar device. The voltage of a good battery should be equal to or exceed 2.1 Volts per Cell (VPC). If the battery’s OCV is lower than the rated value, cell sulphation may have set in. To avoid sulphation, the correct charge voltage should be applied. (NB: VRLA batteries should never be left in a discharged state for prolonged periods.) Reconnect the battery to the system’s load and charging circuitry, ensuring the correct polarities are maintained, i.e. positive to negative etc.
Reconnect the AC mains and carefully measure the ‘float’ charging voltage across the battery terminals with a DVM.
Disconnect the AC supply, leaving the load connected. Check that the battery is now supporting the load, i.e. place a DVM across the battery terminals and check that the voltage has fallen from the ‘float’ voltage to a level controlled by the system’s load. If all seems to be working satisfactorily, reconnect the AC supply.
If the battery fails to support the load for the prescribed time, suspect a battery problem. As battery voltage and capacity are not directly related, checking the OCV for a good voltage does not guarantee a ‘good’ battery. The most accurate method of identifying the status of a VRLA battery is to perform a discharge test using a discharge tester or a conductance tester. A conductance tester measures the internal resistance of the battery. (NB: The relationship between internal impedance of a VRLA battery and the retained capacity change little during the initial and intermediate period of use. As the battery ages, however, retained capacity will start to decrease, which causes the internal resistance to increase. As the battery reaches its end of life, the change of internal resistance will increase rapidly. At this point, the retained capacity of the battery will have fallen below 80 per cent of its rated capacity.
On completion of work, it is advisable to record all relevant details in a battery logbook, or at least complete a label recording the date of battery installation and/or last date of maintenance. Close all equipment doors and make everything safe.
Safety precautions
Before opening up any security system to have a look at the ‘sparky’ bits inside, and when working on or near equipment containing VRLA batteries, it is important to follow a number of general safety rules. These rules can be found in the Safe Working Procedures, under the Electricity at Work Regulations for AC and DC. As VRLA batteries are classified as sealed, no special protective clothing is required to guard against electrolyte spillage. However, to ensure your own safety, it is prudent to follow the following guidelines:
Proper storage for prime condition
Depending on product type and if used in a float application, the operational life of a VRLA battery can now cover 10 to 15 years. Storage or shelf life at 20 deg C ambient temperature ranges between nine and 12 months, starting from a fully charged condition. If storage of 12 months or longer is required, a supplementary top charge is recommended. For maximum service life, the normal operating temperature for a VRLA product is 20-25 deg C. Be warned: heat kills batteries. A high temperature will reduce battery service life quite dramatically and, in extreme cases, can cause an anomaly called ‘Thermal Runaway’ resulting in high oxygen/hydrogen gas production and battery swelling. Batteries are irrecoverable from this condition and should be replaced. Low temperatures will help to ensure a long service life, but batteries used at low temperatures have reduced performance.
When a battery dies
Since September 1997, all VRLA batteries have been classified as ‘Special Waste’. The Special Waste regulations are based on EC Directive 91/689/EEC on Hazardous Waste and apply to everyone who handles ‘spent’ batteries. Enforcement of the Directive is carried out by the Environmental Agency (EA). To avoid falling foul of the regulations, return all spent batteries to the original supplier or to a controlled recycling site.
Finally, if you are unsure about any of the safety or operational aspects associated with the use of VRLA batteries, always check with the supplier or original manufacturer.
