
Chapter 8 ____________________________________________________________ Technical Data
VAISALA______________________________________________________________________ 223
are used by charger software to automatically detect the type of the
connected battery.
External Power Supply
The external DC supply is always connected to POWER connector pins
+ExtDC and GND. The external power supply can be either regulated
or unregulated DC supply (8 ... 30 V) or a solar cell if internal battery is
present. To avoid excessive heating, 8 ... 16 V is recommended.
The required current capability depends considerably on the MAWS
configuration. If there are no optional sensors or other add-ons (radios,
modems, etc.) that require constant powering and measurement
intervals are long (1 minute or more for humidity, temperature, and
pressure), even a few dozen milliamperes are enough to keep the system
alive and slowly charge the battery. If there is no internal battery, then
at least a 200 mA capability is recommended to avoid resetting due to
possible current peaks. If the quickest possible battery charging is
required, then a 1A power supply is recommended.
Solar Cell
When the solar cell is used as an external power supply, a few things
should be kept in mind:
- Always use solar cell in combination with lead battery.
- To achieve the highest possible efficiency, a 6 to 8 V solar cell is
recommended.
NOTE
The condition when external DC supply is used without an internal
battery is automatically detected. In this case, the charger sets its
output voltage to 9.9 V to enable maximum efficiency and minimum
current consumption from supplies of 12 VDC or higher.
NOTE
You can use a 12 V solar cell. However, half of the delivered energy
is lost as heat in the linear charger regulator.
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