The BM-2 is designed to monitor performance of 12 volt lead acid battery systems with capacities of up to 999 Amp hours. It is supplied complete with a precision 200 AMP shunt and a prefabricated cable assembly to enable simple DIY installation. The unit continuously monitors voltage, current (charge or discharge), number of amp/hours (charge or discharge), the batteries state of charge and the time to charge or discharge. This information leads to more efficient use of the battery, which can enhance battery life and reduce the risk of failure.
The minimum information required to monitor the state of charge of a battery is the terminal voltage and the charge/discharge current **. The BM2 measures both these parameters and computes the state of charge using a complex, well proven, algorithm.
A simple and intuitive display shows the service battery voltage, charge/discharge current, state of charge, and time to charge/discharge. The instrument also warns the user when the charge level is too low so that load can be shed or charging commenced to protect the battery. A resettable Amp Hour counter is provided for checking the efficiency of the charging system or keeping a track of power consumption and a second input lets the user monitor the voltage of the starter batter. The simple display format does not mean the internal software is unsophisticated. In fact two separate algorithms are used. One based on integrating amp hours over the charge and discharge cycle, the second based on an adaptive internal mathematical battery model.
A unique feature of the BM2 is its ability to use information from both algorithms, during the charge/discharge cycles, to continually update its performance. This means that, unlike many other systems that rely solely on amp hour integration, the NASA Marine BM2 never needs to be re-synchronised with the battery. The algorithm includes Peukert's equation to ensure accuracy over a wide range of load currents.
The BM2 does all this whist consuming a meagre one and a half milliamps. It is a true battery monitor, easy to install and excellent value for money.
** Some say that they can calculate the state of charge from the terminal voltage only but, as we all know, the terminal voltage falls when the battery is under load and rises when under charge. This fall and rise can be quite substantial, especially when a heavy current is flowing, so how can the terminal voltage be used to calculate anything without knowledge of the magnitude of the current involved?
