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14.9
21X PqWER SUPPLIES
I
The
21X is {vailable with both alkaline batteries
(21X)
and lepd acid batteries
(21XL). The
difference b6tween the 21X and
21XL
is
the
power
supplf base.
Converting
from a 21X to
21XL or
vics versa can be done by simply
purchasing
he
appropriate base.
14.3.'1 21X
ALKALINE
POWER
SUPPLY
The
21X utilizes
I
alkaline
D
cells. Two
screws
must be
from the
front panel to install
the
see Figure 14.3-1.
After
battery
installation,
power switch on
the side
of
the
21X will
the datalogger on and
otf.
To replace
tfe
batteries
without losing the
datalogger
{rogram and data:
1)
do not turn the
power switcfr off, 2)
connect an external battery
to
the
12
voft,
3) remove the old batteries,
4)
replace
with new alkaline
D
cell batteries, and
5) remove the external battery.
A
fresh set df eight alkaline
D
cells has
12.4
volts and
a
/nominal
rating of 7.5 amp-hours at
20oC. The
{mp-hour
rating decreases with
temperature as
shown
in
Table 14.3-1.
Datalogger
fnstruction
10
can be used to
monitor battpry
voltage.
Replace
the alkaline
cells before
the 21X battery voltage drops below
9.6
V.
TABLE 14.3-1. Typical Alkaline Baftery
SBrvice and
Temperature
Temperatute
(oC)
o/o
ol2OoC
Service
20-5q
15
10
5
0
-10
-20
-30
100
98
94
90
86
70
50
30
SECTION
14.
INSTALLATION AND MAINTENANCE
14.3.2 21XL LEAD ACID BATTERY
POWER
SUPPLY
The
21XL includes
a
'12Y,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
alltimes.
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.
lf 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.
lf
the voltage of
the lead acid batteries
drops
below 11.76 volts before recharging,
permanent damage to
the lead acid cells
may
result. CampbellScientific
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.
lf
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
lrom the 21XL in order to measure the actual
lead acid battery voltage.
dala is based on one "D" cell
ions
of 50 mA current drain
ohm
load.
As
the current drain
the
percent service improves for
14-3
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