Raven II Digital Cellular Modem
4
Check that the side preference is correct (step 11 in Airlink manual). To
complete the configuration, proceed to step 13 in the AirLink manual (Write to
Modem).
4. Power Considerations
If the installation’s power supply has a battery charger connected to reliable
AC power, the Raven II can be left on continuously, allowing the station to be
called at any time. If the Raven II is powered continuously, the power
requirements make it unfeasible to power the system from batteries alone for
other than short periods. Most remote installations use solar panels for
charging the batteries.
For continuous year-round power with a datalogger/sensor power requirement
as described below, the MSX20 or MSX20R solar panel is adequate for areas
in the United States other than parts of the Pacific Northwest, great lakes
region, and Alaska. The MSX10 or MSX10R should provide enough power in
the sunnier South and Southwest or if the cellular modem is powered less than
half of the time. (For more information on solar panel sizing check out: BP
Solar’s solar system design guide at:
http://www.bpsolar.com/ContentDetails.cfm?page=61
A power budget can be calculated to determine the length of time the system
will run on fully charged batteries without AC or solar charging. The number
of Amp-hours required per day can be calculated with the following equation:
Amp-Hours per day = (standby current)*(Time in standby) + (Transmitting
current)*(Time Transmitting) + (Average datalogger/sensor current) * 24 hours
If the RavenII is powered continuously and Transmits for 15 minutes per day
this works out to:
Standby (60 mA receiving) = 0.06 A * 23.75 hours = 1.43 Amp-hours
Transmitting (280 mA) = 0.28 A * 0.25 hours = 0.07 Amp-hours
Datalogger/Sensors (2.5 mA) = 0.0025 A * 24 hours = 0.06 Amp-Hours
Total = 1.56 Amp-hours
The datalogger and sensor power requirements above are for a typical weather
station application. (For more information on calculating power requuirements,
refer to Campbell Scientific’s power supply application note, available at:
http://www.campbellsci.com/apnotes.html#misc
With the power budget calculated above, Campbell Scientific power supplies
will allow the cellular system to operate for approximately the number of days
listed below without charging (as might be the case with AC power failure or a
damaged solar panel. The calculation of the ammount of time assumes that the
battery is completely charged at the beginning of the period.