INTRODUCTION
The NASA Clipper BM1/BM2 is supplied complete with display unit,
current shunt (standard 50mV), and connecting cables. They are intended
for operation on 12V Lead-Acid batteries with capacities between 5 and 600
Ampere-hours (Ahr). Their own current consumption is less than 1.5 mA,
which is about 1 Ahr per month, less than the self-discharge rate of most
Lead-Acid batteries.
The NASA BM1/BM2 monitors the battery voltage, the current into and out
of the battery, the total Ahr since it was last fully charged, and predicts the
time to achieve full charge (during charging) or the time to full discharge
(during discharging). A visual indication of the state of the battery charge is
always available, and an alarm is used as an alert when the battery voltage
falls to a preset level.
INSTALLING THE DISPLAY
Safety notes - IMPORTANT
Lead-acid batteries can emit hydrogen when in operation. Hydrogen and air
forms a potentially explosive mixture. Accordingly, ensure that the area
around the batteries is well-ventilated, and douse all naked flames and
prevent sparks.
Short-circuiting a battery with a metal tool or piece of jewellery can cause
catastrophic currents to flow. Before installing any of the BM1/BM2 units,
remove all jewellery (such as rings or metal necklaces). Ensure that no
metal tool can cause a short circuit.
If you are not sufficiently skilled to undertake any part of this installation
safely, you must seek the assistance of a suitably qualified person.
Installation of the Display unit
The installation should be performed in the order specified in the following
sections.
1
Select a convenient position for the display. Cut a hole in the panel
87mm wide and 67mm deep. The site must be flat and the cavity
behind the panel must remain dry at all times. (The cable entry is
deliberately not sealed to ensure adequate ventilation. This prevents
misting of the display).
2
Bring the shunt cable through the hole in the panel.
3
Unscrew and remove the two wing nuts from the rear of the
instrument and remove the stainless steel clamping bracket.
4
Fit the "O" ring seal into the groove in the panel-mounting face of
the instrument. Ensure that it is correctly lying in its groove to
provide the watertight seal for the display before fitting the
instrument to the panel.
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