Science Technology Make a Fire-Powered Smartphone Charger By Megan Treacy Megan Treacy Writer University of South Carolina Megan Treacy is a freelance writer from Austin, TX. A former editor at EcoGeek, she worked as a technology columnist for Treehugger from 2012 to 2018. Learn about our editorial process Updated May 7, 2013 credit: Joohansson Share Twitter Pinterest Email Science Space Natural Science Technology Agriculture Energy Instructables user Joohansson gave us permission to share this neat project for making a fire-powered smartphone charger for your hiking and camping trips. With warm weather upon us, many of you will be hitting the trails with your smartphone. This portable DIY charger will let you keep it topped up with the heat from your camp stove or other heat source and could be used to power other things like LED lights or a small fan. This project is for the more experienced electronics maker. For more pictures and a how-to video, check out the Instructables page. Joohansson gives some background on the charger: "The reason for this project was to solve a problem I have. I sometimes do several days of hiking/backpacking in the wild and I always bring a smartphone with GPS and maybe other electronics. They need electricity and I have used spare batteries and solar chargers to keep them running. The sun in Sweden is not very reliable! One thing that I always bring with me though on a hike is fire in some form, usually an alcohol or gas burner. If not that, then at least a fire steel to make my own fire. With that in mind, I got struck by the idea of producing electricity from heat. I'm using a thermoelectric module, also called peltier element, TEC or TEG. You have one hot side and one cold. The temperature difference in the module will start producing electricity. The physical concept when you use it as a generator is called the Seebeck effect." 1 of 8 Materials credit: Joohansson This is what I used: 1x high temperature TEG module: TEP1-1264-1.5 2x voltage step-up (from this project: http://www.instructables.com/id/Adjustable-Voltage-Step-up-07-55V-to-27-55V/) 1x small heat sink. From old PC (BxWxH=60x57x36mm) 1x Aluminum plate: BxWxH=90x90x6mm 1x 5V brushless DC motor with plastic fan (could be hard to find, check this link) Fixation for heat sink: Aluminum bar (6x10x82mm) 2x M3 bolts+2nuts+2x washers for heat sink: 25mm long 2x M3 1mm thick metal washers 4x M4 bolts+8x nuts+4x washers as construction base: 70mm long 4x M4 1mm thick metal washers 4x M4 bolts: 15-20mm long 4x Drywall screw (35mm) 2x heat insulated washers: Constructed from cardboard and old plastic food turner 80x80x2mm corrugated cardboard (Not very good at high temperatures) 2x pull springs: 45mm extended (Optional) Components for a temperature monitor and voltage limiter. Tools: Drill and thread tap for M3 and M4 File and abrasive paper Screwdriver Pliers Loctite power glue (Repair Extreme) Price: It cost me about 80€ for everything but the most expensive part was the TEG-module (45€). TEG spec: I bought the TEP1-1264-1.5 at http://termo-gen.com/ Tested at 230oC (hot side) and 50oC (cold side) with: Uoc: 8.7V Ri: 3Ω U (load): 4.2V I (load): 1.4A P (match): 5.9W Heat: 8.8W/cm2 Size: 40x40mm 2 of 8 Construction (Base Plate) credit: Joohansson Base plate (90x90x6mm): This will be the "hot side". It will also act as construction base plate to fixate heat sink and some legs. How you construct this depends on what heat sink you are using and how you want to fixate it. I started to drill two 2.5mm holes to match my fixation bar. 68mm between them and the position is matched of where I want to put the heat sink. Holes are then threaded as M3. Drill four 3.3mm holes at the corners (5x5mm from outer edge). Use a M4 tap for threading. Make some nice looking finishing. I used a rough file, a fine file and two types of sand paper to gradually make it shine! You could also polish it but it would be too sensitive to have outside. Screw the M4 bolts through the corner holes and lock it with two nuts and one washer per bolt plus the 1mm washer on the top side. Alternative one nut per bolt is enough as long as the holes are threaded. You can also use the short 20mm bolts, depends on what you will use as heat source. 3 of 8 Construction (Heat Sink) credit: Joohansson Heat sink and fixating construction: Most important is to fixate the heat sink on top of the base plate but at the same time isolate the heat. You want to keep the heat sink as cooled as possible. The best solution I could came up with was two layers of heat insulated washers. That will block the heat from reaching the heat sink through the fixating bolts. It need to handle about 200-300oC. I created my own but it would be better with a plastic bush like this. I could not find any with high temperature limit. The heat sink needs to be under high pressure to maximize the heat transfer through the module. Maybe M4 bolts would be better to handle higher force. How I made the fixation: Modified (filed) aluminum bar to fit in the heat sink Drilled two 5mm holes (should not be in contact with bolts in order to isolate heat) Cut two washers (8x8x2mm) from old food turner (plastic with max temp of 220oC) Cut two washers (8x8mmx0.5mm) from hard cardboard Drilled 3.3mm hole through plastic washers Drilled 4.5mm hole through cardboard washers Glued cardboard washers and plastic washers together (concentric holes) Glued plastic washers on top of aluminum bar (concentric holes) Put M3 bolts with metal washers through the holes (will later be screwed on top of aluminum plate) M3 bolts will get very warm but the plastic and cardboard will stop the heat since the metal hole is larger than the bolt. Bolt is NOT in contact with the metal piece. Base plate will get very hot and also the air above. To block it from heating up the heat sink other than through the TEG module I used a 2mm thick corrugated cardboard. Since the module is 3mm thick it will not be in direct contact with the hot side. I think it will handle the heat. I could not find a better material for now. Ideas appreciated! Update: It turned out the temperature was too high when using a gas stove. The cardboard become mostly black after some time. I took it away and it seems to work almost as good. Very hard to compare. I ́m still looking for a replacement material. Cut the cardboard with a sharp knife and fine tune with a file: Cut it 80x80mm and mark up where the module (40x40mm) should be placed. Cut the 40x40 square hole. Mark up and cut the two holes for M3 bolts. Create two slots for TEG-cables if neccessary. Cut 5x5mm squares at the corners to make place for M4 bolts. 4 of 8 Assembly (Mechanical Parts) credit: Joohansson As I mentioned in previous step, the cardboard cannot handle high temperatures. Skip it or find better material. The generator will work without it, but maybe not as good. Assembly: Mount TEG-module on heat sink. Place cardboard on heat sink and TEG-module is now temporally fixated. The two M3 bolts go through the aluminum bar and then through the cardboard with nuts on top. Mount heat sink with TEG and cardboard on base plate with two 1mm thick washers in between to separate cardboard from the "hot" base plate. The assembly order from top is bolt, washer, plastic washer, cardboard washer, aluminum bar, nut, 2mm cardboard, 1mm metal washer and base plate. Add 4x 1mm washers on the upper side of base plate to isolate cardboard from contact If you constructed correct: Base plate should not be in direct contact with cardboard. M3 bolts should not be in direct contact with aluminum bar. Then screw the 40x40mm fan on top of the heat sink with 4x drywall screws. I added some tape also to isolate screws from electronics. 5 of 8 Electronics 1 credit: Joohansson Temperature Monitor & Voltage regulator: TEG-module will break if temperature exceeding 350oC on hot side or 180oC on cold side. To warn the user I built an adjustable temperature monitor. It will turn on a red LED if temperature reach a certain limit which you can set as you like. When using to much heat the voltage will go above 5V and that can damage certain electronics. Construction: Have a look at my circuit layout and try to understand it as good as possible. Measure the exact value of R3, it is later needed for calibration Place components on a prototype board according to my pictures. Make sure all diodes has correct polarization! Solder and cut all legs Cut copper lanes on prototype board according to my pictures Add needed wires and solder them too Cut prototype board to 43x22mm Calibration of temperature monitor: I placed the temperature sensor on the cold side of TEG-module. It has a max temp of 180oC and I calibrated my monitor to 120oC to warn me in good time. The platinum PT1000 has a resistance of 1000Ω at zero degrees and increases its resistance along with its temperature. Values can be found HERE. Just multiply with 10. In order to calculate the calibration values you will need the exact value of R3. Mine was for example 986Ω. According to the table the PT1000 will have a resistance of 1461Ω at 120oC. R3 and R11 form a voltage divider and the output voltage is calculated according to this: Vout=(R3*Vin)/(R3+R11) The easiest way to calibrate this is too feed the circuit with 5V and then measure the voltage on IC PIN3. Then adjust P2 until correct voltage (Vout) is reached. I calculated the voltage as this: (986*5)/(1461+986)=2.01V That means I adjust P2 until I have 2.01V on PIN3. When R11 reach 120oC, the voltage on PIN2 will be lower than PIN3 and that trigger the LED. R6 works as a Schmitt trigger. The value of it determines how "slow" the trigger will be. Without it, the LED would go off at the same value as it goes on. Now it will turn off when the temperature drops about 10%. If you increase the value of R6 you get a "faster" trigger and lower value creates a "slower" trigger. 6 of 8 Electronics 2 credit: Joohansson Calibration of voltage limiter: That is much easier. Just feed the circuit with the voltage limit you want and turn P3 until the LED goes on. Make sure the current is not too high over T1 or it will burn up! Maybe use another small heat sink. It works the same way as the temperature monitor. When the voltage over zener diode increases above 4.7V it will drop the voltage to PIN6. The voltage to PIN5 will determine when PIN7 is triggered. USB Connector: The last thing I added was the USB connector. Many modern smartphones will not charge if it ́s not connected to a proper charger. The phone decide that by looking at the two data lines in the USB cable. If the data lines is fed by a 2V source, the phone "thinks" it connected to the computer and start to charge at low power, around 500mA for an iPhone 4s for example. If they are fed by 2.8 resp. 2.0V it will start charging at 1A but that is too much for this circuit. To get 2V I used some resistors to form a voltage divider: Vout=(R12*Vin)/(R12+R14)=(47*5)/(47+68)=2.04 which is good because I will normally have a bit under 5V. Look at my circuit layout and pictures how to solder it. 7 of 8 Assembly (Electronics) credit: Joohansson The circuit boards will be placed around the motor and above the heat sink. Hopefully they will not get too warm. Tape the motor to avoid shortcuts and to get better grip Glue the cards together so that they fit around the motor Place them around the motor and add two pull springs to hold it together Glue the USB connector somewhere (I did not find a good place, had to improvise with melted plastic) Connect all cards together according to my layout Connect the PT1000 thermal sensor as close as possible to the TEG-module (cold side). I placed it beneath the upper heat sink between the heat sink and cardboard, very close to the module. Make sure it has good contact! I used super glue that can handle 180oC. I advise to test all circuits before connected to the TEG-module and start heating it You are now good to go! 8 of 8 Testing and Results credit: Joohansson It is a bit delicate to get started. One candle for example is not enough to power the fan and soon enough the heat sink will get as warm as the bottom plate. When that happen it will produce nothing. It must be started quickly with for example four candles. Then it produce enough power for the fan to start and can start cool off the heat sink. As long as the fan keeps running it will be enough air flow to get even higher output power, even higher fan RPM and even higher output to USB. I made the following verification: Cooling fan lowest speed: 2.7V@80mA => 0.2W Cooling fan highest speed: 5.2V@136mA => 0.7W Heat source: 4x tealights Usage: Emergency/read lights Input power (TEG output): 0.5W Output power (excluding cooling fan, 0.2W): 41 white LEDs. 2.7V@35mA => 0.1W Efficiency: 0.3/0.5 = 60% Heat source: gas burner/stove Usage: Charge iPhone 4s Input power (TEG output): 3.2W Output power (excluding cooling fan, 0.7W): 4.5V@400mA => 1.8W Efficiency: 2.5/3.2 = 78% Temp (approx): 270oC hot side and 120oC cold side (150oC difference) The efficiency intend the electronics. The real input power is much higher. My gas stove has a maximum power of 3000W but I run it at low power, maybe 1000W. There is a huge amount of waste heat! Prototype 1: This is the first prototype. I constructed it at the same time I wrote this instructable and will probably improve it with your help. I have measured 4.8V@500mA (2.4W) output, but have not yet run for longer periods. It's still in the test phase to make sure it's not destroyed. I think there is a huge amount of improvements that can be done. Current weight of the whole module with all electronics is 409g Outer dimensions are (WxLxH): 90x90x80mm Conclusion: I don't think this can replace any other common charging methods regarding efficiency but as an emergency product I think it ́s quite good. How many iPhone recharges I can get from one can of gas I have not yet calculated but maybe the total weight is less than batteries which is a bit interesting! If I can find a stable way of using this with wood (camp fire), then it ́s very useful when hiking in a forest with an almost unlimited power source. Improvement suggestions: Water cooling system A light weight construction that transfer heat from a fire to the hot side A buzzer(speaker) instead of LED to warn at high temperatures More robust insulator material, instead of cardboard.