BM-1 Battery Monitor
BM-1 Battery Monitor

The BM-1 is designed to monitor performance of 12 volt lead acid battery systems with capacities of up to 600 Amp hours. It is supplied complete with a precision 100 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. It also monitors the voltage of the engine strat battery. This information leads to more efficient use of the battery, which can enhance battery life and reduce the risk of failure.

Fully monitors domestic battery/bank

Monitors voltage of engine start battery


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 AMP

Cables supplied:
100 AMP shunt link to M8 Ring terminal.
5 Metre from display unit to battery - fused and fitted with ring terminals for shunt, fuse holder and M8 ring terminal to battery.

Display unit

Standard 110mm square Clipper case. High contrast LCD, backlit for night viewing.
Minimum voltage visual alarm
Simple operation - 4 keys to select backlight, Volt/Amp/State of Charge screen,
AMP hours or Time to run.

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?



DOWNLOAD one battery wiring diagram
Sailing Today BM-1


Price: £87.50 ( £105.00 Inc. VAT)
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