Video: BVS – Product

Video transcript

Why a capacity test needs every cell watched, and how the BVS does it: what it measures, how the system is built, and what it tells you during and after the discharge. A capacity test discharges a whole battery bank for hours. Measuring only the string voltage hides the one cell that is failing, and a single weak cell can end the test early or put the whole backup supply at risk. Standards from IEC, I triple E and NERC ask for the cell voltages to be recorded during the test.

The BVS is a modular system. A cell voltage module sits on each cell. The modules are chained on one communication bus back to a control unit, which powers them, collects the data and passes it to a PC. Optional string modules add the voltage and current of the whole string. Each module measures its cell up to 30 volts with a resolution of one millivolt, and the inter-cell connection up to 50 millivolts with a resolution of one microvolt. The string module goes up to 600 volts, and a scan can be taken as often as every second.

Everything meets at the control unit. In come the cell and inter-cell voltages from up to 128 modules, the string voltage and current, and 4 ambient temperatures. Out go the data to the PC and to the internal memory card, the alarm, and the 66 volt supply that powers every module. There are two versions. In the BVS each module takes one cell and also measures the connection to the next. In the BVS-4 each module takes 4 cells,

so a large bank needs fewer modules and less wiring. The inter-cell measurement is what finds a bad connection rather than a bad cell. A loose or corroded link heats up and drops voltage under load. Each module receives the potential of the previous cell through the communication cable, so it measures the drop across the link without an extra wire. When a cell reaches its limit, the red LED on its own module lights, and the alarm on the control unit flashes. With the discharge unit connected, the software can pause the test,

show which cell has to come out, and recalculate the string limits for the cells that remain. The test then continues. The bus is built so that one failure stays one failure. If a module stops working, the others keep talking to the control unit, and the missing cell is simply marked. And if the link to the PC is lost, the data are still on the control unit's memory card and can be imported afterwards. During the test the software shows every cell at every scan:

as a table, as a histogram or as a line chart. The weakest cell stands out in the histogram without reading a single number. After the test, results can be compared with an earlier discharge of the same bank. A cell that ended lower this year than last, or that falls faster, is the one to replace or watch, before it fails in service. With the discharge unit, the cell data and the discharge data end up in one file and one report. And with the optional string voltage and string current modules,

the BVS records the whole test with any load bank on the market. Its place is wherever a battery bank is the last line of supply: substations, power plants, generator excitation, protection and control systems, telecoms and UPS rooms. In figures: 90 to 264 volts of mains supply, USB or Bluetooth to the PC, two gigabytes of internal memory, and a control unit that weighs under a kilogram. Battery maintenance, from Amperis.