Introduction: Thermoelectric USB Charger - Off Grid Electricity.
The device has a nimh power pack which stores electrical energy for use whenever you need it, the power pack can be detached for use anywhere. The output is 5V through a USB port. This device would work especially well were there is snow available for extra cooling – for example off grid cabins in remote (snowy) locations. It could serve as dual purpose - melting snow for water and producing electricity ? The bigger the temperature difference between the two sides of the peltier the greater the power output.
This idea is not new, it has been around for a long time. See here for some very
old thermoelectric generators
The peltiers produce 0.6W of power to recharge the battery pack.
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Here's what you'll need :
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Step 1: Tools and Materials
- 2 x TEC-12706 Peltier Modules
- DC-DC USB Step Up converter
- Small switch
- Project box
- Small scrap of vero board
- 4 x 3000mah nimh/ni-cd batteries
- 1N4001 diode.
- Battery holders for the batteries
- Miscellaneous wire, solder etc.
- Thermal compound
- Aluminium or copper milk pan
- PC CPU Heatsink
- 4 M4 x 12 bolts
- 4 Long (>75 mm) M6 bolts for the feet
- Electrical connectors (screw terminal type)
- Silicone tubing.
- Drill & drill bits
- M4 Tap
- Soldering iron
- Spanners to suit the bolts
Notes: The PC heat-sink must be big enough for the two peltiers to sit on.
I bought the DC-DC converter on ebay, it has an integral USB port.
Step 2: Mark Out Holes in the Pan for the Heat-sink Bolts
The heat-sink will be bolted to the milk pan. Mark 4 holes to for bolts to go through the milk pan into the heat sink. The sizing of these holes will depend entirely on the heat-sink
Step 3: Drill Holes in the Pan to Attach the Heat-sink
Drill out the holes you marked. The drill size should be 4mm
Step 4: Drill and Tap Holes in the Heat-sink for the M4 Bolts
Drill matching holes in the heat-sink with a 3.2mm and cut an M4 thread in these holes.
Step 5: Lay Out the Peltiers
Lay the peltiers onto the heat-sink, ready for the dry fit. It's best to do a dry fit first to make sure that everything lines up properly. When you're ready to assemble the pan for good, apply thermal compound to both sides of the peltiers.
Step 6: Bolt It Together
Bolt the pan to the heat-sink using the M4 bolts. Make sure the peltiers are sandwiched neatly in between.
Take care not to overtighten the bolts as this could crush the peltier chips.
Step 7: Slip Some Silicone Tubing Over the Wires
Slip some silicone tubing over the electrical wires to help protect them from the heat. This also makes the wires a bit neater.
Step 8: Add Legs
Drill four 6mm holes around the edge of the pan for the feet (bolts).
Step 9: Attach the Legs
Bolt the four legs onto the pan.
Step 10: Attach the Screw Terminal Blocks
Bolt the screw terminal to the side of the pan using two M3 x 20mm bolts.
Step 11: Connect It All Up and Test
Connect the two peltier chips in series using the screw terminals. Light some candles underneath the thermoelectric pan and fill the pan with water.
Connect a multimeter to the output and measure the voltage. If the voltage is very low, such as 0.1 – 0.5 volts, then one of the peltiers is probably connected the wrong way around. Flip the wires around on one of the peltiers.
It will take around 5 minutes for the heat-sink to reach full temperature, at this point you should see between 3 – 7 Volts DC output.
Step 12: Build the Step Up Circuit
Solder up the circuit for the step up converter. The peltiers are connected to the battery pack through the 1N4001 diode. The step up converter is connected to the battery pack through the switch.
Note: The 3.5mm jack shown was not used in the final build.
Step 13: Fit It All Into the Project Box
Cut out the holes in the project box for the switches and USB port. The USB board is glued to the scrap of strip-board to keep it securely in place and the strip-board fits into the slots in the project box.
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