Campbell Scientific CR7 Measurement and Control System - Manual (Page 147)

SECTION 14. INSTALLATION
14-3
Battery voltage should NOT be allowed to
drop below 11.76V before recharging;
otherwise, permanent damage to the lead
acid cells may occur. CSIs warranty does
NOT cover battery or cell damage resulting
from deep discharge.
Avoid deep discharge states by periodically
monitoring voltage level of the CR7s internal
batteries, using Input/Output Instruction 10.
Incorporate the battery voltage measurement to
the data acquisition program to avoid deep
discharge of the CR7 internal batteries.
All external charging devices must be
disconnected from the CR7 in order to measure
the true voltage level of the internal batteries.
The internal lead acid batteries of the CR7 will
continue to discharge with the CR7 turned on
but not scanning or processing data. This
quiescent current drain will vary depending on
the number of I/O Modules, Excitation and
Pulse Counter cards contained in the CR7, and
the number and type of external devices
powered by the CR7's Power Supply. Users
can approximate the quiescent current drain of
their specific CR7 System from the information
provided in Table 14.2-2.
TABLE 14.2-2. Calculating Quiescent
Current Drain
Module/Card Current Drain
Control Module 0.4 mA
I/O Module 2.5 mA
Excitation card 2.0 mA
Pulse Counter card 0.8 mA
Analog Input card 0.7 mA
As an example, the quiescent current drain of a
CR7 System containing a Control Module, an
I/O Module, 1 Excitation card, 2 Pulse Counter
cards and 4 Analog Input cards is about 9.3mA.
At this rate of quiescent current drain, fully
charged internal batteries (2.5 AH) are depleted
to a full SAFE discharge level (11.76V) after
268 hours (about 11 days). When the CR7 is
active, it draws approximately 100mA so the
actual current drain is a function of the program
being executed.
14.2.2 SOLAR PANELS
Auxiliary photovoltaic power sources, such as
Solarex Models MSX5, MSX10, and MSX18
Solar Panels may be used to maintain charge
on lead acid batteries.
TABLE 14.2-1. Solar Panel Specifications
MSX5 MSX10 MSX18
Typical Peak Power 4.2 8.9 18.6
(Watts)
Current @ Peak
.27 .59 1.06
(Amps)
Amp Hrs/week
6.4 14.4 26.4
NOTE: Specifications assume 1 kW/m2
illumination at a panel cell temperature of
25oC. Individual panel performance may
vary as much as 10%.
When selecting a solar panel, a rule-of-thumb is
that on a stormy overcast day the panel should
provide enough charge to meet the system
current drain (assume 10% of average annual
global radiation, kW/m2). Specific site
information, if available, could strongly influence
the solar panel selection. For example, local
effects such as mountain shadows, fog from
valley inversion, snow, ice, leaves, birds, etc.
shading the panel should be considered.
Guidelines are available from the Solarex
Corporation for solar panel selection called
"DESIGN AIDS FOR SMALL PV POWER
SYSTEMS". It provides a method for
calculating solar panel size based on general
site location and system power requirements. If
you need help in determining your system
power requirements, contact Campbell
Scientific's Marketing Department.
The solar panel is connected to the CR7 by
attaching the 2 lead wires of the power cable to
the terminal block located on the charging
regulator circuit board (Figure 14.2-1). The free
end of the solar panel power cable is equipped
with a 12V power plug for use with the 21XL
Micrologger. Cut this plug off with side cutters
and remove about 1.5" of the cable's outer
insulation. Remove about 0.5" of insulation
from the exposed black and clear leads. The
BLACK lead is GROUND and the CLEAR lead
is positive (+).