General Information
1-16 Rev 2/01
1.7.2 Determining Auxiliary Power Consumption
In determining power requirements for auxiliary devices such as a radio or cell phone, the duty cycle
for the device must be estimated. The duty cycle is the percentage of time the device is transmitting
(TX). For example, if a radio is transmitting 1 second out of every 60 seconds, and for the remaining
59 seconds the radio is drawing receive (RX) power, the duty cycle is:
Duty Cycle = TX time/(TX time + RX time) = 1 sec/60 sec = 0.0167
To calculate the total power consumed by a radio, obtain the power (P) consumption values for
transmit and receive from the radio manufacturer’s literature, then use the following equation to
calculate the power consumption for a particular duty cycle:
Power = (P
TX
x
Duty Cycle) + [P
RX
(1 - Duty Cycle)]
Determine the power consumption for all devices that use power from the EF-Series Unit, and enter
the total calculated value in Table 1-1.
1.7.3 Totaling Power Requirements
To adequately meet the needs of the EF-Series system, it is important to determine the total power
consumption, size of solar panel, and battery backup requirements accordingly. For total EF-Series
Unit power consumption, add the device values in Table 1-1. Although Table 1-2 takes into account
the power supplied by the EF-Series Unit to its connected devices, be sure to add the power
consumption (in mW) of any other devices used with the EF-Series Unit in the same power system, but
not accounted for in the table.
Convert the total value (in mW) to Watts by dividing it by 1000.
mW / 1000 = Watts
For selecting an adequate power supply, use a safety factor (SF) of 1.25 to account for losses and other
variables not factored into the power consumption calculations. To incorporate the safety factor,
multiply the total power consumption (P) by 1.25.
P
SF
= P
x
1.25 = _____ Watts
To convert P
SF
to current consumption in amps (I
SF
), divide P
SF
by the system voltage (V) of 12 volts.
I
SF
= P
SF
/ V = _____ Amps
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