For outside use in winter, I decided to make some heated insoles. You can put several layers of clothes on the rest of your body, but packing your shoes can be uncomfortable. Mine are made to be functional and cheap, but if you're concerned about aesthetics, spend a bit more on the material.
I bought carbon fiber cloth from ( www.carbonheater.us ) and you need 60 cm for each insole.
Carbon Fiber Tape works by electric resistance, you run current through the tape and it heats up. Heated clothing made from wire works the same way, but wire is more fragile to bending and use. Tape also heats more evenly.
15mm tape has about 18 ohms resistance per meter.
32mm tape has about 8.9 ohms resistance per meter.
In this example I'm using 15mm tape. I cut a 60cm long strip and sew the ends together. I place the negative lead and positive 30 cm apart. This creates 2 x 30 cm carbon fiber tape in parallel. The calculation looks like this :
18 Ohm x 0.3m = 5,4 Ohm
3,7V : 5.4 Ohm = 0.6A
0.6A x 2 (parallel) = 1.3A
1.3A x 3,7V = 4.8 Watt per insole.
I also made insoles with wider tape, so I can use a 5v power bank as a power source. Use the calculation to find what suits you best. For example : Use 44mm tape, 65cm long strip with leads in each end (NOT parallel), powered by 5V (USB power bank) and you will get about the same Watt.
You will need :
Carbon Fiber Tape
DC adapter male and female - or connector of your own choice.
Wire - flexible soft silicone - 22 AWG
Battery - 18650 Li-Ion - or power source of your own choice.
Step 1: Glue the Carbon Fiber Tape to the Insole.
Put the hemming web in the desired pattern, put carbon fiber tape on top and run a clothes iron along the carbon fiber tape. This will melt the hemming web and effectively glue the carbon fiber tape to the insole.
Step 2: Sew the Wires to the Tape and Apply Glue
Sew the positive and negative lead wire to the tape. I chose to first glue the tape to the insoles, then sew the wires to the tape. That way the thread will hold also in the insole, and less chance of stretching / damaging the tape.
Then you apply silver conductive wire glue to the wire. The glue conducts electricity and will make a better and stronger connection between wire and tape.
Step 3: Put Fabric on Top of Insole
Put fabric of your choice on top of the insole. In the picture I used fabric from a retired parachute, glued on with hemming tape.
Step 4: Chose a Power Source and Connector Type.
One 3,7V 18650 Li-Ion battery works good as power source, and gives a lot of power in a small format.
Make sure to buy battery from a known brand :
Both give about 2 hours + run time.
LiFePO4 cells have slightly lower voltage and gives a bit less heat, but is known to be a stable and safe battery chemistry.
Put connector of choice on the insole wires. I chose a DC plug for easy unplugging. SAE, banana plug etc can also be used.
I made an USB - DC plug adapter so it can also be used with power bank.