Battery Testing - NFPA 72, 2019
NFPA 72 made some significant changes to battery testing requirements in the 2019 edition. Previous editions of NFPA 72 identified types of tests based on the type of battery being tested. Different requirements applied to lead-acid type, nickel-cadmium type, and sealed lead-acid type (the most common type in modern fire alarm systems).
NFPA 72, 2016 Edition, requirements for sealed lead-acid type batteries included replacement based on manufacturer recommendations, charger test to verify proper charging voltage, discharge test to test load test the battery per manufacturer instructions, and a load voltage test to test battery performance under alarm load conditions. The replacement, charger, and discharge tests were required annually, and the load voltage test semiannually.
In the 2019 Edition of NFPA 72 the battery testing requirements were updated to reflect current industry standards and eliminate batteries not commonly used fire alarm systems. The new testing requirements are intended to ensure that fire alarm batteries provide a reliable source of secondary power by focusing on battery replacement, capacity (load) testing, and alternative test methods.
The first thing you may notice is that NFPA 72 changed the term used to describe the most common battery in modern fire alarm systems to a term used by battery manufacturers and the IEEE: VRLA (valve-regulated lead-acid). VLRA batteries are defined in Chapter 3 as a sealed lead-acid cell with a valve that opens when the internal pressure exceeds a set amount. The most common type of VRLA battery is the AGM (absorbed glass mat), where the electrolyte material is held in fiberglass mats that surround the plates.
Before testing the batteries, NFPA 72 requires that the person conducting the test verify that all system software stored in volatile memory is protected from loss. Depending on the system, this may mean ensure that the system is not in programming mode or operating in any condition where normal system operation has not been restored.
A semiannual temperature test is required upon opening the cabinet door. The test needs to be measured at the negative terminal using an infrared thermometer. Any with a temperature greater than 18 degrees F above ambient must be replaced.
A semiannual charger test is conducted with the battery fully charged and connect to the charger. A voltmeter is used to measure the voltage across the battery, and then verified against the equipment manufacturer’s recommendations. If the voltage is outside the limits, the charger must be adjusted or replaced.
A semiannual cell/unit voltage test is conducted with the battery fully charged and connect to the charger. A voltmeter is used to measure the voltage across each cell/unit of the battery. A battery must be replaced if any cell/unit measures a voltage less than 13.26 volts.
Ohmic testing is conducted during initial installation when the battery is installed to establish a baseline ohmic value, and then semiannually to test performance. For the baseline value, data provided by the manufacturer may also be used.
Ohmic testing is a method of testing battery health by measuring the battery’s internal resistant. Typically, ohmic testing uses one of three techniques: conductance, impedance, or resistance to take the measurements.
Ohmic testing is based on Ohm’s Law, which states the relationship between volts, amperes, and ohms in a circuit. Ohmic testing uses the voltage and current to measure the resistive characteristics of the battery’s cells. As batteries age, they degrade and lose capacity. The degradation causes the internal resistance of the battery to increases, decreasing the battery’s ability to accept and hold a charge.
A key part of ohmic testing is establishing a baseline. Every battery has a unique ohmic “signature”, so ohmic testing upon initial installation provides the most accurate measurement. However, if this information is not available, baseline data from the battery manufacturer may be used. Ideally, the ohmic value is tested at least 72 hours after installation to allow the battery to stabilize.
Semiannual testing is conducted with the battery fully charged and connected to the charger. The battery must be replaced when any cell/unit deviate from the established baseline by 30 or more for conductance and 40% or more for resistance or impedance.
A replacement/load test is required every 3 years. The load test requires load testing the battery per manufacturer’s specifications for a discharge rate for 3 hours or more until the terminal voltage decreases to the end voltage specified by the manufacturer. The test duration is used to calculate the battery capacity based on ambient temperature. The battery must be replaced if the capacity is less than or equal to 80%, or at the next scheduled test if capacity is less than 85%. This test is also permitted to be conducted in lieu of an ohmic test.
NFPA 72, A.18.104.22.168 provides more detailed guidelines for ohmic and replacement/load testing.