Adnan 2 Posted August 10, 2015 Share Posted August 10, 2015 Hi, I need to provide my launchpad with solar panel energy harvesting with 500F supercapacitor. 50 - 100 ma charging current is sufficient and the solar panel provides 2.5V. input voltage 0.5 - 3 volt output voltage 3 volt Any suggestion about the voltage regulator to be used? Thanks. Quote Link to post Share on other sites
Antscran 35 Posted August 10, 2015 Share Posted August 10, 2015 Hi Adnan, I have made a few energy harvesting circuits now and usually use Linear Technology IC's, they offer a good range of options. TI also do a range of devices as well as do other manufacturers, but I am less familiar with these. You need to use a boost or similar topology (Sepic) if you want to have the system running when the solar cell is below the loads running voltage. Unsure of the power output of your solar cell, but this will determine the charging speed of your supercapacitor at any given irradiance level and load requirements. I have not used the voltage range that you require, but the LTC3105 should fit your requirements. The circuit calculations are easy enough and the datasheet walks you through everything you need. Hope this is of some use, Ant Adnan 1 Quote Link to post Share on other sites
chicken 630 Posted August 10, 2015 Share Posted August 10, 2015 TI has the MSP430 Solar Energy Harvesting kit: http://www.ti.com/tool/ez430-rf2500-seh It's on the pricey side, but the documentation including schematics might be useful even when not buying the kit: http://www.ti.com/tool/ez430-rf2500-seh#Technical%20Documents Adnan 1 Quote Link to post Share on other sites
Adnan 2 Posted August 10, 2015 Author Share Posted August 10, 2015 Hello Antscran Thanks for your reply. I want to ask you about the characteristics of solar panel (voltage) that should be used with 2.7v supercapacitor. I'm confused about using voltage regulator twice between solar panel and supercapacitor as well as between supercapacitor and the MSP430 launchpad. The sunlight in my country is available most of the daytime. So I hypothesis that there is no need to exhaust the energy. The range of variation between 2.7 and 2.0V may be sufficient. Quote Link to post Share on other sites
Lgbeno 189 Posted August 11, 2015 Share Posted August 11, 2015 Have you looked at this thread? http://forum.43oh.com/index.php?/topic/8274-Cheap-solar-battery-%2B-wireless-IoT-node Many of these solar lights use either a AAA or AA NiMh battery that charges to around 1.2V. This voltage can be easily be boosted to 3.3V. In the direct sunlight I got about 85mW of power from the panel which should be plenty for a sensor node. The 2.7v supercap is inconvenient unless you run your whole circuit at 2.7V. Sent from my iPhone using Tapatalk Quote Link to post Share on other sites
arashed31 1 Posted August 11, 2015 Share Posted August 11, 2015 Hello Adnan! Another chip you may be interested in is the BQ25504 or the BQ25570. Both chips have a boost converted designed to charge a super cap or Li-ion battery and can do so with solar panel voltages as low as 0.3 V (perfect for your solar cell). The second chip, BQ25570, has a buck converter that you can tune to 3 volts, limited to 100mA. These chips are meant to be 80-90% efficient. bluehash 1 Quote Link to post Share on other sites
Adnan 2 Posted August 12, 2015 Author Share Posted August 12, 2015 Launchpads and RF components are provided with internal voltage regulator, that is the reason why these components can be supplied with a wide range of input voltages (2 - 3.6 V). So, I want to run the system on 2.7V (typical voltage of supercapacitor). On ebay I found many cheap regulators ($2 - $5) that can be used to adapt the output of solar panel to the supercapacitor voltage. I'm hesitated about using these products because I'm no sure about the reliability of these products. Another problem I expect to encounter is how to tackle the problem of voltage drop of supercapacitor below 2V which may be occurred rarely. The motivation of using a cheap energy harvesting circuit is to reduce the cost of the whole system. Rickta59 1 Quote Link to post Share on other sites
dubnet 238 Posted August 12, 2015 Share Posted August 12, 2015 I would second what @@Lgbeno suggested. His circuit in the thread he referenced would allow input voltages ranging from 0.9V to a little over 5V with a 3.3V regulated output. The efficiency of the circuit is pretty good too. If I remember correctly the MSP430 Value line chips have an operating range of 2-3.6V but at the lower voltages you may have to adjust your clock speed. This is not regulation but the specified operating range of the MSP430. The Launchpad board has a 5V to 3.3V regulator to bring the USB voltage down to the operating range of the MSP430 MPU. If you are using a circuit like lgbeno's you would bypass the onboard regulator and feed the MSP430 directly via the header on the lower right corner of the board. Be sure to disconnect the jumpers that feed power back to the programming portion of the board so that you are only powering the MSP430. Quote Link to post Share on other sites
Lgbeno 189 Posted August 12, 2015 Share Posted August 12, 2015 Launchpads and RF components are provided with internal voltage regulator, that is the reason why these components can be supplied with a wide range of input voltages (2 - 3.6 V). So, I want to run the system on 2.7V (typical voltage of supercapacitor). On ebay I found many cheap regulators ($2 - $5) that can be used to adapt the output of solar panel to the supercapacitor voltage. I'm hesitated about using these products because I'm no sure about the reliability of these products. Another problem I expect to encounter is how to tackle the problem of voltage drop of supercapacitor below 2V which may be occurred rarely. The motivation of using a cheap energy harvesting circuit is to reduce the cost of the whole system. Cheap regulators often have high quiescent current so I would look into that. Also in solar, some special consideration needs to be given for the MPPT of the solar panel because the panel will stop producing power if it's voltage is pulled too low. By far the cheapest way to do this is with the $1 solar light and the boost converter method. The ASIC inside the solar light handles the MPPT and NiMh charging, then the boost gives your circuit the right voltage. SuperCaps don't really store as much energy as batteries and they are more expensive. They are arguably more reliable for larger pulses of current but I don't think that it matters in this case. You can boost to whatever voltage you like based on part selection as well. I started using NCP1400 for cost but I think the TPS61097A-33 is lower power. Regardless, I figure I can get about 1 year out of a single AA battery so I think that is good enough. Adnan 1 Quote Link to post Share on other sites
Adnan 2 Posted August 13, 2015 Author Share Posted August 13, 2015 I can afford any voltage regulator regardless of their cost. But my goal is to design a sensor node that can lasts several years without any maintenance with minimum cost. Rechargeable battery has limited charging cycles and should be replaced when it's reached the limit, that is the reason why I prefer using supercapacitor. Designing energy harvesting circuit is out of my interest, It is just a tool to accomplish my design, So I need simple, cost effective, and ready to use harvesting circuit because I want to emphasize on protocol design and launchpad programming. Many options available, and I just want one that can charge supercapacitor with minimum cost and effort. Quote Link to post Share on other sites
Lgbeno 189 Posted August 13, 2015 Share Posted August 13, 2015 BQ25504 looks like your ticket then. Taiyo Yuden has some decent super caps. Sent from my iPhone using Tapatalk bluehash and Adnan 2 Quote Link to post Share on other sites
Adnan 2 Posted August 13, 2015 Author Share Posted August 13, 2015 Comparing TPS61097-33DBVT with BQ25504 shows that It requires less number of external components and provide constant output at 3.3V. There is aversion of this product that ca output constant 2.7V which is suitable to charge 2.7V supercapacitor. I think it may be better choice. Quote Link to post Share on other sites
Lgbeno 189 Posted August 14, 2015 Share Posted August 14, 2015 Comparing TPS61097-33DBVT with BQ25504 shows that It requires less number of external components and provide constant output at 3.3V. There is aversion of this product that ca output constant 2.7V which is suitable to charge 2.7V supercapacitor. I think it may be better choice. I cringe to see all of those resistors... Just remember that BQ25504 and TPS61097 are not functionally the same. TPS61097 isn't going to do MPPT on a solar panel although maybe one additional resistor to limit the charging current into the super cap would be all that you need. This also assumes that you have a panel that has Open voltage of a few 100mV less than 2.7. Sent from my iPhone using Tapatalk Adnan 1 Quote Link to post Share on other sites
Adnan 2 Posted August 14, 2015 Author Share Posted August 14, 2015 You're right. Now, I have two options BQ25504 and LTC3015 and I should decide which one will be more suitable. LTC3015 is designed to work with solar panel. but I'm not sure about BQ2554. By the way what is the difference between BQ25504 and BQ25570? Quote Link to post Share on other sites
Lgbeno 189 Posted August 14, 2015 Share Posted August 14, 2015 I think BQ2554 has an integrated buck converter. LT parts are usually a little better and easier to use that TI but you pay the premium. You should select your solar panel first though to make sure that it is compatible with the charger solution. Sent from my iPhone using Tapatalk Quote Link to post Share on other sites
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