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User Manual May 2019 | Page 14/28
USER MANUAL
Energy Harvesting Magnet Contact Transmitter Module
STM 320 / STM 329 / STM 320U
(Stepcode DE and later)
3.5
Energy consumption
Following diagram illustrates a complete cycle in standard mode which starts with controller
active phase (setup, measurement etc.) immediately followed by a telegram transmit. After
short sleep phase the controller will get active two times and send two telegrams.
Prerequisites for example calculation:
-
Internal energy storage MS412FE with usable capacity of about 0.7 mAh
https://www.sii.co.jp/en/me/datasheets/ms-rechargeable/ms412fe-5/
(voltage range 2.4 - 3 V at 25 °C)
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Solar cell ECS 200 delivers at 200 lux about 5 µA
https://www.enocean.com/de/enocean-module/details/ecs-300/
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Power consumption wake-up and transmit cycle standard mode: 100 µAs
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Power consumption wake-up and transmit cycle secure mode: 140 µAs
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10 reed contact changes per day (e.g. 5x window open/close)
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Average leak current of STM 3xy at 25°C: 0.5 uA
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Wake-up cycle 20 - 25 min (average 1.500 s) for status telegram
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8 h light per day (24 h) light @ 200 lux and 25°C
Example calculation of the energy consumption with following parameters:
- Current consumption (depending on amount of wake-ups due to reed contact change):
* Current consumption for status telegrams and sleep:
100 uAs / 1,500 s + 0.5 uA = 0.57 uA
* Power consumption for 10 reed contact changes incl. additional transmits per day:
100 uAs / (60 x 60 x 24 s) = 1.2 nA = 0.0012 uA)
* Average current consumption: 0.57 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 – 0.57 uA) = 636 h = 27 days
- Average operation time in darkness when fully charged (3.0 V to 2.4 V):
0.7 mAh / 0.57 uA = 1,228 h = 51 day
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