The multi-purpose Battery Symmetry Relay BMSA is designed to monitor and give an early warning if one or more cells are performing different from an average cell in the battery. The battery must consist of two blocks of cells coupled in series with an accessible middle point used as a reference potential. No current will be drawn from the middle point. The Symmetry Relay monitors that the positive and the negative battery blocks perform equally independent of the actual charge and load level.
The two battery blocks do not need to be of equal voltage (same number of cells), but the individual cells must be equal and have the same history. The BMSA accepts up to twice as many cells in one block as in the other. The nominal voltage range of each block can be set from 12V to 256V and the actual voltage must be within the range of 9 to 300V allowing a battery voltage ranging from 18V to 600V.
For high battery voltages exceeding 300V the middle point connection is critical. If it can (even accidentally) be disconnected, the maximum battery voltage must be kept below 300V. As an option, the BMSA can be extended to monitor the actual battery voltage for under and over voltage. The option will include individual relays for under and over voltage.
Application
The BMSA is used on batteries in back up supplies where, by matching two batteries against each other, a warning can be given as soon as a cell in one of the battery blocks starts to deteriorate. As the BMSA is not depending on the actual charge and load status, it is a powerful supervision of only occasionally used batteries in emergency systems.
