Campbell Scientific CR10X Measurement and Control System - Manual (Page 221)

SECTION 14. INSTALLATION AND MAINTENANCE
14-5
source is the same as connecting two lead acid
batteries in parallel, causing one battery to drop
voltage and the other to raise voltage. Alkaline
batteries connected to the external port must
have a diode in series to block charging which
would cause an explosion. (The PS12ALK
battery pack has this diode.)
Monitor the power supply using datalogger
Instruction 10. Users are strongly advised to
incorporate this instruction into their data
acquisition programs to keep track of the state
of the power supply. If the system voltage level
consistently decreases through time, some
element(s) of the charging system has failed.
Instruction 10 measures the voltage at the 12 V
port, not the voltage of the lead acid battery.
External power sources must be disconnected
from the CR10X and charging circuit in order to
measure the actual lead acid battery voltage.
TABLE 14.3-2. PS12LA, Battery, and AC
Transformer Specifications
PS12LA
Input Voltage
16 to 26 VDC or
16 to 26 VAC RMS
Output Temperature
compensated float
charge
Maximum Battery
Capacity
24 Ahr
Temperature range
with NA 7-2 battery
-25 to +50
°C
Lead Acid Battery
Battery Type
Yuasa NA 7-12
Float Life @ 25
°C
5 years typical
Capacity 7.0 amp-hour
Shelf Life, full charge Check twice yearly
Charge Time (AC Source) 40 hr full charge, 20
hr 95% charge
AC Transformer
Input:
120 VAC, 60 Hz
Isolated Output: 18 VAC @
1.11 A max.
There are inherent hazards associated with the
use of sealed lead acid batteries. Under normal
operation, lead acid batteries generate a small
amount of hydrogen gas. This gaseous by-
product is generally insignificant because the
hydrogen dissipates naturally before build-up to
an explosive level (4%) occurs. However, if the
batteries are shorted or overcharging takes
place, hydrogen gas may be generated at a rate
sufficient to create a hazard. Campbell
Scientific makes the following
recommendations:
1. A CR10X equipped with standard lead acid
batteries should NEVER be used in applications
requiring intrinsically safe equipment.
2. A lead acid battery should not be housed in
a gas-tight enclosure.
14.3.3 PS512M VOLTAGE REGULATOR WITH
NULL MODEM PORTS
The PS512M 12 Volt Lead Acid Power Supply
with Charging Regulator and Null Modem Ports
is used when 5 volts is needed to power
external modems besides the capabilities of the
PS12LA. The PS512M supplies 5 volts to pin 1
of the 9 pin null modem ports, otherwise the
capabilities and functions are identical to the
PS12LA. A common use for the PS512M is in
radiotelemetry networks. The PS12LA cannot
be modified to a PS512M.
The maximum current drain on the 5 volt supply
of the PS512M is 150 milliamps.
14.4 SOLAR PANELS
Auxiliary photovoltaic power sources may be
used to maintain charge on lead acid batteries.
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/m
2 ). 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.