User guide

Appendix A. Sample Data Transfer Calculations
A-2
Power Calculation
When configuring a power supply (i.e. solar panel and battery) for a remote
station it is essential to design with the worst case scenario in mind. This
will help to ensure that the station will perform as expected.
The power calculation for data transfer can be carried out now that the transfer time is
known. The modem has the following power consumption characteristics:
- 0 mA when powered off
- 300 mA stand-by
- 800 mA transmit (2500mA max)
The time slot for powering the modem must be long enough to allow for the
complete downloading of the datalogger’s data and connection times. Refer to
Table 2 or make your own calculation based on the collection interval you intend
to use.
It is advisable to make the time slot longer than the minimum download time
required to allow for initial connection times and possible retries. It is also
advisable to arrange the time slot during a time of day when the power supply is
its most robust. For a solar powered station this would be the early afternoon.
The periods of power consumption in a day can be divided up as follows:
Period A: the modem is powered off – 0 mA
Period B: the modem powered up in stand-by mode – 300mA
Period C: the modem is transmitting the data – 2500mA
Now consider a 35 Kbyte data file size and a datalogger programmed power time
slot of 1/2 hour; the Periods above become:
Period A = 24 hours - Period B – Period C
Period B = 30 minutes – Period C
Period C = 3.5 minutes (from Table 2)
We can substitute in the Period B and C values to obtain all Periods:
Period A = 23.5 hours = 0.0 Ah/Day
Period B = 26.5 minutes @ 130 mA = 0.065 Ah/Day
Period C = 3.5 minutes @2500 mA = 0.1458 Ah/Day
The total draw for the data transfer is the sum of the periods, 0.2108 Ah/Day, one
day per week.
The Ah/Day calculation for each period is as follows:
= Current Draw in mA * (Interval in minutes / 60 min) / 1000
NOTE
NOTE