Megger BITE 3 Battery Impedance Tester

Megger BITE 3 UPS Battery Impedance Tester

The Megger BITE3 Battery Impedance Test Equipment determines the health of lead-acid cells up to 2000 Ah by taking measurements of the most important battery parameters. The BITE3 measures cell impedance, an internal ohmic test, cell voltage, intercell connection resistance and ripple current. And, for the first time in a battery instrument, the BITE3 measures float current and the harmonic content of the ripple current. There is even a built-in spectrum analyzer to show the harmonic content of the ripple current. It has firmware that can be upgraded through the Internet and supports multiple languages.

The BITE3 is one of the easiest instruments to use. Its measurements, along with temperature, specific gravity and other battery data, can provide the best basis for evaluating the overall health of batteries from terminal plate to terminal plate and to a lesser extent, the charger (from ripple current and its harmonic content.) Megger recommends that the BITE3 be made part of a comprehensive battery maintenance program with readings taken and recorded semi-annually for flooded, lead-acid cells and quarterly for VRLA.

Unlike load-cycle testing which is expensive, non-predictive and time-consuming (but does provide actual capacity data), the BITE3 is quick, reliable and easy to use. With a rapid test time, one person can easily, quickly and precisely measure cell and string parameters without taking the system off line. Furthermore, in as little as four keystrokes, the instrument is ready to take battery measurements (five, if the power button is included). The processor of the BITE3 uses a Windows® CE Operating System and can store more than 1 million cells’ data in any string configuration. It is menu-driven that is easy to navigate. Its unique data analysis screens provide immediate feedback on the status of cell impedance, (see Figure 1, Battery Analysis Report). The first part of the report is the numerical data. The second part is the impedance deviation graph and the third part is the impedance deviation graph but in ascending impedance order. The ascending impedance graph groups the weakest cells together for easier analysis. With the optional printer, this report can be printed by the user and left at the site as a record for future reference.

APPLICATIONS It is known that impedance is correlated to battery capacity and there has been a long-standing question as to when a user should replace a cell. See Figure 2. Recent studies by EPRI* and other organizations indicate that when the impedance of a sealed battery increases by about 50% from its baseline value, the cell has degraded to less than about 70% capacity. BITE3 and PowerDB allow the user to trend data and to enter baseline values for comparison purposes and to make decisions whether on-site or in the office. Both the BITE3’s impedance deviation graph and the trend graph in PowerDB clearly show the status of a cell which helps users to decide what action needs to be taken to ensure battery back up reliability based on users’ criteria.

A battery’s internal impedance increases as its capacity decreases due to various factors such as age, ambient temperature, discharge history, etc. The BITE3 measures internal impedance and dc voltage for lead-acid cells up to 2000 Ah in capacity. It also measures intercell connection resistance, float current and ripple current and the harmonic content of the ripple current to provide a much better evaluation than any other single instrument. Impedance finds electrical path problems due to plate sulphation, post-seal corrosion, dry-out (loss of compression), poor intracell welds and intercell connections and more. These data let the user determine maintenance needs such as:

• Cell replacement criteria based on impedance trends
• Jumper out a cell or two
• Clean and/or retighten intercell connectors
• Shorten the maintenance interval, etc.,
• Evaluate float current and ripple current effects

Typical installations that can be tested using the BITE3 include:

Electrical power generation plants

Substations — utility, railroad, industrial

Telecommunications facilities — OSP, Wireless, POPs, MTSOs, Fiber Regens

UPS systems — standard and cabinetized batteries

Railroad — Signals and Communications, CTC

Aircraft power supplies

Marine and military