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User Manual May 2019 | Page 31/49
USER MANUAL
Scavenger Transmitter Module
STM 330 / STM 331 STM 331U / STM 332U / STM 333U
(Stepcode DE and later)
3.14
Energy consumption
Current Consumption of STM 33x
For energy calculations following values are used:
Internal energy storage MS412FE with usable capacity of about 0.7 mAh
https://www.sii.co.jp/en/me/datasheets/ms-rechargeable/ms412fe-5/
(usable voltage range 2.4 - 3 V at 25 °C)
Solar cell ECS 200 delivers at 200 lux about 5 µA
https://www.enocean.com/de/enocean-module/details/ecs-300/
Power consumption transmit cycle standard mode: 100 µAs
Power consumption internal sensor measurement: cycle 30 µAs
Current is proportional to illumination level (not true at very low levels!)
Average leak current of STM 3xy at 25°C: 0.5 uA
Example calculation of the energy consumption with following parameters:
- Requirements for example calculation:
* configuration: wake cycle 100 s and min. transmit every 10
th
wake up
* 8 h light per day (24 h) light @ 200 lux and 25°C
- Current consumption (depending on amount of wake-ups due to temperature change):
* Min. current consumption with no wake-up cycle due to temperature changes:
30 uAs / 100 s + 100 uAs / 1000 s + 0.5 uA = 0.9 uA
* Maximum current consumption with max. wake-up cycles due to temperature changes :
30 uAs / 100 s + 100 uAs / 100 s + 0.5 uA = 1.8 uA
* Average current consumption: (0.9 uA + 1.8 uA) / 2 = 1.35 uA
- Average solar power harvested: 5uA / (8 h / 24 h) = 1.67 uA
- Time to fully charge energy storage (2.4 to 3.0 V) at stable temperature:
0.7 mAh / (1.67 uA – 0.9 uA) = 909 h = 38 days
- Average operation time in darkness when fully charged (3.0 V to 2.4 V):
0.7 mAh / 1.35 uA = 519 h = 22 days
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