Video: BLU

Video transcript

How the BLU is connected to a battery, alone, with a current probe, in parallel or with cell monitoring, and how a capacity test is run. A backup battery is only as good as the time it can really hold the load. The one test that proves it is a controlled discharge: a known current or power, drawn until the end voltage, while the voltage and the capacity are recorded. Nine models cover strings up to 800 volts, with discharge currents up to 300 amps and power up to 42 kilowatts, all set and watched on a 7 inch touch screen.

Everything is on the front panel: the touch screen, the current terminals and the voltage sense sockets, the current probe input, the ports for cell monitoring and for a second unit, the emergency stop, and the earth stud. It ships with the PC software, the USB, mains and earth cables, and a case. The current cables come in pairs with insulated clamps, sized to the model. Sense cables, a current clamp and cell modules are added as needed. Before any cable goes on:

disconnect the charger from the battery, and check the battery for damage or leaks. Earth the BLU first. Then the cables go into the instrument, and only then onto the battery. A single unit is the simplest case. After the earth, the red current cable goes to the positive of the first cell and the black one to the negative of the last cell. The sense cables are optional: they read the string voltage without the drop along the current cables.

With the current probe the battery can stay on its load. The clamp goes around the battery cable, and the BLU adjusts its own current so that the total stays at the set value. With the probe on the load side instead, the same mode drives extra load units. When one unit is not enough, up to 10 of the same model work in parallel. Each is earthed and wired to the string, and a network cable links EXT OUT on the master to EXT IN on the slave. The master distributes the current across the units.

To see which cells give up first, every cell is watched. One module per cell, chained to the BLU with communication cables, and the sense leads go into the module first, then onto the cell. The test is set up on the screen in 6 fields: the mode, the test type, the value, the limits, cell monitoring and the battery information. Templates can be prepared in the office and simply loaded at the site. Four ways to load the battery:

constant current, constant power, constant resistance, or constant voltage, where the current falls once the voltage is reached. Profiles split the test into intervals to reproduce a real duty cycle. Four limits decide when the test ends: the string voltage, the time, the capacity, and, with cell monitoring, the voltage of each cell. Each one has a warning level that only alerts, and an end level that stops, or pauses, the test.

During the discharge the screen shows the voltage curve, the current or power, the capacity so far and the limits. The value can be changed without stopping, and the test paused to take out a bad cell. At the end the result is stored: time, final voltage, and capacity in ampere hours and as a percentage of nominal. It can be corrected to 25 degrees per IEEE 450 or IEEE 1188, and marked pass or fail.

Three rules. Never disconnect a cable during the test: it can draw a DC arc. After the stop, let the unit cool for 60 seconds before switching off. And after a mains failure, the test resumes by itself 60 seconds after power returns. The messages name the cause. Inverse voltage: cables the wrong way round. Open connection: a current cable came off. Overheating, overvoltage and a fan failure stop the test. The PC software controls the test and builds the report.

The BLU works on the batteries of power plants, substations, telecoms, data centres and protection systems, and can fully discharge banks before recycling. Battery testing, from Amperis.