AN209: STM 300 THERMO OR BATTERY POWERED
Contents
1. APPLICATION NOTE 209 Green Smart Wireless enocean STM 300 THERMO OR BATTERY POWERED Power Supply Alternatives to Solar Panel Applications based on STM 300 C in environments without enough Illumination Alternatively to the use of a standard solar panel e g in applications with no or not enough light the STM 300 300C module can also be powered by another suitable external power sources like i e a thermo generator based on a standard Peltier Seebeck element and the EnOcean ECT 300 energy harvester or even a small low cost Li MnO2 coin battery Background in sleep mode the supply current of the STM 300 C module is typically 0 2 pA In operation the current consumption strongly depends on the frequency of wake ups and radio transmissions so the average current over time has to be considered for calculation of the module average current consumption see Fig 1 below more details see chapter 2 11 of the STM 300 C User Manual 100 _h 0 01 Current mA 0 001 0 0001 0 00001 O 10 20 30 40 50 60 70 80 90 100 Time ms Fig 1 Current Consumption of STM 300 C Module Average Current Consumption and power source considerations Calculation Example Cyclic measurement with transmission every 100 s Using the table from chapter 2 11 of the STM 300 C User Manual the required continuous supply current depending of Wake cycles and Transmit interval settings can be easily f2. 22 uW of continuous input power delivered by the Peltier ele ment are therefore required The energy storage device C Fig 3 at the ECT 300 output has now two functions it must store the continuous delta T K Fig 4 delivered low energy i e 4 4 uWs between two consecutive transmissions i e for 100 seconds and deliver the required peak currents Please note in this case that at least 2K permanent temperature difference between the both sides of the Peltier element must be always available otherwise the use of an appropiate en ergy storage management circuit is recommended e g see STM 300 C User Manual 3 1 For more details about specific system performance and considerations regarding thermo generator dimensioning please consult the ECT 300 and EDK 300 C user manuals EnOcean www enocean com Subject to modifications Christian Bach Feb 2010 Page 2 3 APPLICATION NOTE 209 Green Smart Wireless enocean Disclaimer The information provided in this document describes typical features of the EnOcean radio system and should not be misunderstood as specified operating characteristics No liability is assumed for errors and or omissions We reserve the right to make changes without prior notice For the latest documentation visit the EnOcean website at www enocean com
3. anganese dioxide lithium 3 V coin battery can be used Depending on the energy demand different capacity sizes can be chosen Generally please consider the limited life time behavior of batteries even if the energy balance calculation indi cates a multiple year operation time It also could be useful to have a control of the supply voltage to know in time when the battery voltage fails below a certain limit to be changed before failure The circuitry described in the Application note AN309 can be used to do this Using a Thermo generator ECT 300 Peltier element as power supply Fig 3 Considering again the Table 1 relation same scenario I STM 1 6 uA and considering a STM 300 C supply voltage of 2 7 V results the ae ECT 300 long term averaged required power at the Peltier DC DC Heat sink 1000p F transmitter to send every 100 seconds Heat P U x I or P 2 6 Vx1 6 UA 4 4 uW Fig 3 An ECT 300 based thermo generator Following diagram shows a typical ECT 300 performance in combination with Peltier ele would deliver this power by gt 2 K ment TEC2L 15 15 5 6 and heat sink SK 426 Performance will be affected by variance temperature difference as shown in of components and environment air flow etc Fig 4 ECT 300 User Manual The Peltier element output voltage 12 5 mV K is in this case only 25 mV Considering for the ECT 300 at this absolute lowest operational input voltage a conversion efficiency of 20 about
4. ound Wake Transmit Current required cycle interval cont operation s According the mentioned table first second and last column see Table 1 a STM 300 C needs a 1 6 pA continuous current to wake up every 100 seconds Wake cycle 100 and transmit by every Wake Transmit Interval 1 I_STM 7 1 6 pA Table 1 EnOcean www enocean com Subject to modifications Christian Bach Feb 2010 Page 1 3 Te APPLICATION NOTE 209 Green Smart Wireless enocean STM 300 THERMO OR BATTERY POWERED Power Supply Alternatives to Solar Panel Using a Battery as power supply Even a small battery capacity of 0 150 Ah a coin cell CR2032 has gt 0 230 Ah would theo retically mean about 10 years continuously function for this setting 150 mAh 0 0016 mA x X h gt X 150 mAh 0 0016 mA 93750 h 3900 days Bearing in mind that the energy of a battery cannot be fully STMI00 C drawn for this purpose means only approx 50 of its nominal capacity until the voltage drops below about 2 2 Fig 2 V a single CR2032 coin cell still allows more than 8 years l of continuous function In these 8 years the STM 300 C can wake up and transmit more than 2 5 millions times Please notice that in order to ensure the needed peak current capability of approx 40 mA without damage the coin cell battery must be buffered by an external low leakage capacitor not on STM 300 C included see Fig 2 For low cost applications standard m
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