Specifications

12/16/97 4 - 5
The AOM enables the modem at 5 minutes past each even-numbered hour (according to the time clock in the
Console) and keeps it enabled for four minutes. When a communication is received, the modem remains
enabled during the data transfer and for two minutes thereafter; no communication is interrupted.
The Timer can be set to any intervals the user selects. Any radio communication in progress when the Timer
switches OFF will be interrupted. (Exception: a cell-phone call will not be interrupted.)
The “Charge Budget, “ discussed below, is one means of determining the amount of time that the radio may
be on each day.
CHARGE BUDGET
When using the radio in a solar/battery-powered station, one must limit the power drawn by the radio. This
means limiting the time that the radio is ON, enabled to receive messages, and -- in most cases -- limiting
even more severely the duration of transmissions.
The Charge Budget table (on page 10) gives a worksheet and an example of a charge budget, used to
calculate the daily battery drain for various ON and TRANSMIT durations. The sheet is also used to
estimate the daily charge available to the battery from the solar panel.
Charge Drain per Day
Lines A, B, C, and D of Table 2 sum up the current drains over the day.
A: A Monitor II station with Link draws 16 mA, a GroWeather or EnviroMonitor station draws 18 mA.
B: The Alarm Output Module, when in Power-Save mode, draws 2.4 mA continuously. The Timer current
may be considered zero when the relay is not energized; it draws 12 mA when the relay is closed.
C: This is the current drawn by the radio when on (see the equipment data section). The Neulink 9600
Modem/transceiver, for example, draws 100 mA when on. The YDI draws 180 mA.
D: This is the additional current drawn by the radio when transmitting. The Neulink draws an additional
800 mA. The YDI draws essentially zero additional current.
The total current drawn, in Amps (mA/1000), multiplied by the ON time in minutes gives the charge drain in
Amp-minutes.
The Example in Table 2 is for a GroWeather station using the Timer to turn the Neulink 9600 radio ON for
four six-minute periods each day. It assumes that two three-minute calls are made each day to read out the
data.
Charge Gain per Day
Lines E, F, G, and H provide parameters for calculation of the average charge that the solar panel provides to
the battery each day.
E: The charging current provided by the solar panel when solar irradiance is 1000 Watts per square meter.
The panel included with the Davis solar Power Kit provides 0.6 Amp.
F: The solar irradiance at solar noon at the station site, in W/m
2
.
G. The length of the day, in hours.
H. A multiplier to account for cloudiness or other factors which may limit the average sunlight reaching the
panel throughout the day. Note that even during cloudy conditions at least 20% of the radiation usually
gets through.
The total charge gain is then --
(Rated Panel Current) x (Peak Irradiance/1000) x 0.55 x (Day Length in minutes) x “Cloud Factor.”
The factor 0.55 includes battery efficiency and the integration of the solar cosine effect over the day.
The charge GAIN/DRAIN ratio gives the number of days of operating charge accumulated on an average
day.
Note that in GroWeather and EnviroMonitor stations the battery voltage is measured by the weather station
and reported via WeatherLink, so you can monitor the voltage and reduce or cease communication if it