Megger BITE3 - Battery Impedance Test Equipment

The BITE3 from Megger is a battery impedance tester for determining the health of lead-acid cell batteries up to 2000Ah. “BITE” stands for Battery Impedance Test Equipment. The BITE3 is a powerful unit, capable of testing important parameters including cell impedance, internal ohm test, cell voltage, intercell connection resistance, and ripple current. Unlike any other battery impedance testers on the market to date, the BITE3 is also able to measure float current and the harmonic content of ripple current. The unit features an integrated spectrum analyzer to determine this harmonic content.

The BITE3 is extremely simple to use. In addition to its primary battery testing functions, the unit can also perform simple temperature and specific gravity tests to give users as much battery data possible in order to evaluate batteries to the best possible extent. For the most comprehensive battery testing possible, Megger recommends that the BITE3 be used as part of an extensive battery maintenance regiment with semi-annual and quarterly readings, depending on application.

The BITE3 provides a quick, reliable, and easy alternative to expensive and time-consuming load-cycle testing. With the BITE3, a single user can rapidly and accurately measure cell and string parameters without having to take systems offline. Once the unit has powered up, the user is only 4 keystrokes away from performing these tests. This is thanks to the Windows CE processor with 32 MB memory built into the BITE3. This menu-driven system is easy to navigate and provides storage for data from up to 1 million cells, no matter the string configuration.

The BITE3 features an auto cell/strap recognition function which eliminates the need for complex configurations, regardless of the battery string configuration. The device can be used during typical installations performed at electrical power generation plants, substations, telecommunications facilities, UPS systems, railroads, and aircraft power supplies as well as in marine and military applications. Ideal for testing parallel strings, the BITE3 measures escape current so there is no need to sectionalize the strings. This helps to avoid false negative readings.

PowerDB Battery Management Software

PowerDB is a powerful software package that allows you to organize and analyze recorded battery test data from the BITE3. The software is a perfect tool for those who must meet NERC and FERC requirements. PowerDB allows users to configure the BITE3 device as well as transfer data directly from the unit to the software for more streamlined analysis.

Once data is loaded, PowerDB will allow you to trend voltages, impedances, strap resistances, and cell temperatures as well as specific gravity. PowerDB will also display the ripple current, float current, and ambient temperature, with the option to include an IR picture, diagram, or other graphics. Users can select red, yellow and green bands to quickly and easily compare cells versus warning and failure limits. This makes it quick and easy to identify individual weak cells or old strings. This will help provide longevity for your strings. In addition, the BITE3 paired with PowerDB will allow you to see how the batteries in your strings are aging. This will allow you to predict their estimated life span for easy budgeting.

Power DB comes in two versions. The freeware version, PowerDB LITE, is included with the BITE3. This freeware version still provides all the features listed above. In addition, PowerDB LITE also calculates baseline data, average impedance, and average strap values. Users can also input their own logos and view their data in either line charts or bar charts.

The full version of this software, PowerDB, is available for purchase from Megger. It supports all the functions of PowerDB LITE, plus it works with almost all Megger products and allows users to merge data from different products into one report. The full version also allows users to create custom reports.

Data Analysis

PowerDB has the ability to download site and string information and data as well as firmware updates to the BITE3. This gives the BITE3 consistent access to the most recent data for the strings being tested during the upcoming week or month. With previous data loaded, better analyses can be performed simply by comparing the last result to the most recent result. Any cell change of more than a few percentage points suggests that further investigation is warranted.

Applications

Those with experience in battery testing know that impedance is correlated to battery capacity. A battery’s internal impedance increases as its capacity decreases due to various factors such as age, ambient temperature, and discharge history. The question of whether or not to replace a cell is usually at the center of an impedance test. 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 combined with PowerDB allow the user to trend data and enter baseline values for comparison purposes. Both the BITE3’s impedance deviation graph and the trend graph in PowerDB will clearly show the status of a cell. This is helpful when users must decide what action needs to be taken to ensure battery back-up reliability.

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

BITE3 Testing Procedure

To measure impedance with the BITE3, attached a lead set at the cell terminals to measure the voltage drop of the AC current signal applied by the instrument to the cell while it is on-line. During each measurement, impedance is calculated following Ohm’s Law, displayed on the LCD screen, and then stored internally. The BITE3 can also measure, display, and record DC voltage, interconnection (strap) resistance, float, and ripple currents. Float and ripple current measurements are performed separately at the start of the test because current is the same everywhere in the series connection of the string, in accordance with Kirchhoff’s law.

This testing procedure utilizes an innovative, patent-pending measuring technique so that a clamp-on current sensor is no longer necessary.

It is well-recognized that the best way to measure current is with a shunt. Since the battery has many straps, simply by determining a strap’s resistance, it can be used as a shunt to determine float and ripple currents. First, while across an intercell connector, the instrument applies a current and measures the voltage drop of the intercell connector to calculate the resistance of the intercell connector. Then, it measures the strap again without the instrument current. The unit performs a calculation to determine float and ripple currents and the intercell connection resistance.