There are three types of capacity tests, the Acceptance Test, the Performance Test, and the Service Test. The acceptance test is made at the beginning life of the battery and is usually performed at the factory or at the location of installation. The test is based on the design capacity of the battery. The performance test which is also based on the battery design capacity is typically performed two to three years after installation and then every five years based on IEEE recommendations. The service test is based on the load and is used to determine if the battery will correctly supply the load. The test is performed as needed.
Capacity testing is the single absolute test when it comes to the ability to determine whether a battery is going to be capable of supplying the amount of current for the designed amount of time. There are some drawbacks however:
- First, every battery has a certain number of deep discharges it can tolerate before failure, so each time a discharge test is performed some of the life is taken away.
- The second drawback is the complexity, cost and time to correctly perform a discharge test.
If the system being tested is in service, a backup system will need to be installed while the main system is tested. This is done in the event of a power outage occurring during the capacity test. A temporary external load comparable to the normal load being served will need to be connected to the main system under test. The time of the test can last as long as the rating on the battery.
Capacity testing requires equipment (load bank, data collection devices, back-up power –generator or temporary battery bank, etc…). Battery knowledge is also important. A technician needs to be able to detect and jump out a bad cell during testing and must be capable of making a decision to interrupt testing. Once a cell voltage falls below 1.75 volts (lead-acid styles), it will decline at a rapid rate, and the testing should be interrupted before that particular cell goes into reversal. A test can be halted while the bad cell is bypassed –for 10% of total test time.
Capacity testing requires a fully charged battery properly floated at recommended voltage, balanced cell potentials, and acid gravities. Some cases may require an equalize charge to be performed. The battery to be tested must be on float for at least 72 hours prior to test. This is especially important following equalization. All connections (inter-cell, inter-row, and inter-aisle) must be optimized to lowest resistances. Usage of a proper discharge load is also very important to a well-executed capacity test.
Prior to embarking upon a capacity test give Protec Equipment a call. Our experienced staff can provide you with the proper equipment and guidance to ensure success on your next job. Protec stocks a complete line of battery maintenance and diagnostic equipment in our large rental inventory. We carry all the top manufactures: Alber, Megger, and Storage Battery Systems.