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3.2
Electrical installation
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3.2.1
Power supplies and consumption
Your choice of power source needs to suit your application. You can use an internal lithium battery (not rechargeable)
but for now you must use an external 5 to 24 Vdc power source (could be solar, wind, a larger battery, or a 110/230 Vac
to 6-24Vdc power supply). The supply needs to be quite well regulated and capable of delivering a peak of 0.5A.
Important: only configure the unit to operate in power states 1 (GPRS pollable), 2 (SMS pollable) or 3 (transmit on power
up). Power state is part of the system command.
The power consumption will vary depending on how the unit is programmed. If Powering from the internal battery then
be sure to configure the ‘modem power scheme’ as ‘power off between transmit events.’
When ‘asleep’ the device will draw approximately 85 micro amps.
Please note that the battery capacity quoted by the manufacturers is not always fully available to the Metron2. Please
consult Powelectrics for advice on how long the battery will last in your application.
The current consumption varies depending on the state of the unit. The figures below are based on a power supply
between
3.6 to 4.2 volts.
Deep sleep
85 micro amps (screen, sensors and GSM modem off)
Screen on
add 28mA
USB connected
add 8mA
GSM on
(in ‘polling’ mode)
add 24mA (typically)
During analogue read now
add 50mA average
– depends on settling time per sensor but allow at least 5 seconds
The device will not function correctly if the supply voltage is between 4.2 and 5 volts.
If the supply voltage is greater than 5v there is additional components are in use within the Metron2 and it therefore
draws 2mA in ‘deep sleep’ mode. If you intend to use in an application where the power demand is too great for the
integral battery option (Metron2/SSM) then you will need to consider this and select the supply accordingly.
When the unit is communicating over GSM/GPRS the current consumption fluctuates over time and varies depending on
the signal strength. The length of time the communications takes depends on how long it takes to charge the on board
super-capacitors, how long it takes to register onto the network and how long communications takes (with GPRS
communications t is up to the host to ‘kill’ the connection).