Operator`s manual

SECTION 14. INSTALLATION AND MAINTENANCE
14-3
14.3 21X POWER SUPPLIES
The 21X is available with both alkaline batteries
(21X) and lead acid batteries (21XL). The
difference between the 21X and 21XL is the
power supply base. Converting from a 21X to
21XL or vice versa can be done by simply
purchasing the appropriate base.
14.3.1 21X ALKALINE POWER SUPPLY
The 21X utilizes 8 alkaline D cells. Two screws
must be removed from the front panel to install
the batteries, see Figure 14.3-1. After battery
installation, the power switch on the side of the
21X will turn the datalogger on and off.
To replace the batteries without losing the
datalogger program and data: 1) do not turn the
power switch off, 2) connect an external battery
to the 12 volt, 3) remove the old batteries, 4)
replace with new alkaline D cell batteries, and
5) remove the external battery.
A fresh set of eight alkaline D cells has 12.4
volts and a nominal rating of 7.5 amp-hours at
20
o
C. The amp-hour rating decreases with
temperature as shown in Table 14.3-1.
Datalogger Instruction 10 can be used to
monitor battery voltage. Replace the alkaline
cells before the 21X battery voltage drops below
9.6 V.
TABLE 14.3-1. Typical Alkaline Battery
Service and Temperature
Temperature (
o
C) % of 20
o
C Service
20 - 50 100
15 98
10 94
590
086
-10 70
-20 50
-30 30
NOTE: This data is based on one "D" cell
under conditions of 50 mA current drain
with a 30 ohm load. As the current drain
decreases, the percent service improves for
a given temperature.
14.3.2 21XL LEAD ACID BATTERY POWER
SUPPLY
The 21XL includes a 12V, 2.5 amp-hour lead
acid battery, a AC transformer (20V DC), and a
temperature compensated charging circuit with
a charge indicating diode. An AC transformer
or solar panel should be connected to the 21XL
at all times. The charging source powers the
21X while float charging the lead acid batteries.
The internal lead acid battery powers the
datalogger if the charging source is interrupted.
The 21XL lead acid battery specifications are
given in Table 14.3-2.
The connector from the charging source can be
inserted into the receptacle on the side of the
21XL. A transzorb provides transient protection
to the charging circuit. A sustained input
voltage in excess of 40V will cause the
transzorb to limit voltage.
Solar panels and AC transformers should be
supplied with a connector. If trying to use a
charging source which has only two bare leads
(no connector), contact Campbell Scientific for
identification of the proper connector.
The red light (LED) on the 21XL is on during
charging. The switch turns power on and off,
battery charging still occurs when the switch is
off.
If the voltage of the lead acid batteries
drops below 11.76 volts before recharging,
permanent damage to the lead acid cells
may result. Campbell Scientific does not
warrant batteries.
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 12V
port, not the voltage of the lead acid battery.
External power sources must be disconnected
from the 21XL in order to measure the actual
lead acid battery voltage.