User manual

Toolbox 32 User Manual 1.47d www.cse-semaphore.com/mykingfisher
Page
13
Average Current Consumption
The average current consumption is calculated by multiplying the fraction of time that the LP-2/3 is in each
mode by the current consumption of that mode. These currents are then totaled to provide the average
current consumption.
Example: An LP-2/3 has one 900 MHz Spread Spectrum Radio option board. The LP-2/3 continuously
sleeps for 9 minutes, awakes for 1 minute (with all output voltages and port enabled) and then sleeps again.
While awake it transmits for 1 second (1/60=0.0167 minutes). The LP-2/3 also has two digital inputs (assume
both are active) and one current analog input (assume worst case of 20 mA / 100%).
The average current consumption (during each 10 minutes and therefore during the entire day) is:
State
Time In State
Current Draw
(mA)
Weighted Current Draw
Sleeping 9 mins every 10 mins 2 9/10 x 2 = 1.8
LP-2/3 running with voltages
and ports enabled
1 min every 10 mins 40 + 8 + 5 + 4 1/10 x 57 = 5.7
Two digital inputs ON 1 min every 10 mins 2 x 0.4 1/10 x 0.8 = 0.08
One analog input @ 20mA 1 min every 10 mins 56 1/10 x 56 = 5.6
Radio transmitting 0.0167 mins every 10
minutes
120 0.0167/10 x 120 = 0.20
Radio receiving 1 – 0.0167 mins every
10 mins
44 (1-0.0167)/10 x 44 = 4.3
Average Current Consumption:
18
mA
(rounded up)
Battery Backup
For maximum battery life, a maximum discharge depth of 50% is typically used. Eg. for a 7 AH (Amp Hour)
battery, there is 3.5 AH of backup power. Therefore the battery can supply 3.5 Amps for 1 hour or 1 Amp for
3.5 hours etc.
The minimum size of the backup battery required depends on how long the LP-2/3 needs to be able to run
without mains or solar power.
Min. Backup Battery = (LP-2/3 Average Current Consumption [mA] / 1000) x Backup Time (hours) x 2 AH
Therefore, for the above example, the minimum backup battery required to power the LP-2/3 for two days
(48 hours) of no power (or adequate sunlight) is:
Minimum Backup Battery = (18 / 1000) x 48 x 2 = 1.8 AH (rounded up)