DAVIS CELLULAR TELEPHONE ANTENNA KIT User Manual download pdf (Page 7)

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/m2.

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 drops

too low. It is suggested that communication be limited whenever the battery voltage is less than 12.5 Volts; if

WeatherLink Radio Communications 7

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DAVIS CELLULAR TELEPHONE ANTENNA KIT User Manual Page 7