Nasa BM1 Battery Monitor

Technical Specification

• Supply voltage: 8 - 16 Volts DC 
• Supply current: 1.5 milliamps 
• Battery capacities: 5 - 600 AMP Hour
• Load current: 100 AMPS Maximum
• Charge current: 100 AMPS Maximum
• Shunt Standard: 50 millivolt @ 100 AM

How does it work?

The minimum information required to monitor the state of

charge of a battery is the terminal voltage and the

charge/discharge current **. The BM1+ 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 battery.
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 BM1+ 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 BM1+ 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 BM1+ 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?