Fishing from a pontoon boat or float tube during late Fall, Winter, or early Spring can be tough on your feet, which are usually hanging in the water. Chemical toe warmers don't work very well for me, so I made these electric socks. They can be run from the 12 V battery for an electric motor, sonar, or from a portable rechargeable pack. I don't use an electric motor but have a portable 6 Amp-Hour unit that fits nicely in the pocket of my waders when in my float tube. In my pontoon boat I have the option of using the 12V battery for my portable sonar.
Please note that you should limit the current from your source as a precaution in the event of leaky waders.
Step 1: Sew Carbon Tape to a Flexible Shoe Insole
I made my own insole out of some upholstery fabric. I traced my foot onto paper, cleaned up the trace lines, cut the paper, traced the outline of that paper onto some upholstery fabric, and cut out the fabric. Pin the carbon tape to your insole and sew it on. You'll want to use a sewing machine for this step.
I wear a men's size 11 and used roughly 1 meter per foot of this 15mm wide carbon fiber heater tape (from www.carbonheater.us). You can tune your own design from the Ohms/meter specification of your carbon tape and V^2 / R for your wattage. Based on the manufacturer's specification of 19 Ohms per meter, I estimated my design at (12 V)^2 / 19 Ohm = 7.5 Watts per foot, but my end result was 14 Ohms and 10 W per foot. For me, 12 V was the most convenient power supply, and also the only reasonable source for obtaining my target of at least 7.5 W per foot with a reasonable length of tape. You could get by with less tape by concentrating it in the toe area, but then you'll need a lower supply voltage in order to keep the amperage and wattage reasonable.
At 12 V / 14 Ohm = 0.86 A per foot, my source needs to supply 1.7 A to achieve the full 10 W per foot, and a reasonable safety fuse would be in the 2 to 3 A range. My portable 6 Ah source should theoretically run both feet for about 3.5 hrs, but I will be surprised to get 3 hrs out of it (I have not run them for that long).
If you want more power, reduce the overall resistance by shortening the length of carbon tape, or connect sections in parallel. If you want less power, lengthen the tape, which would be a bit challenging here. You could try to double back that center strip of tape, but you have to be careful to not let the edges of the tape overlap (doing so would create a parallel circuit). You might be able to find a source for a narrower tape that has a higher resistance per meter. It may also be possible to increase the resistance by narrowing the tape that you have. However, you can't just cut off an edge or it will fray, but it might be possible to trim the edges once it has been sewn down. You can also reduce power by using a variable power source or control circuit (see the last step).
Step 2: Attach Lead Wires to the Ends of the Carbon Tape
Use a wire ampacity chart (such as this one) to determine the minimum wire gauge for your current. In my case I could get by with wire as small as 22 AWG, but decided to go no smaller than 20 AWG. I ended up using some left over speaker wire that I believe is 18 AWG. It was a bit stiffer than the 20 AWG, but not any bulkier because of a thinner insulation layer.
I attached the wires to the end of the carbon tape by first fanning and flattening the stripped ends of the wire and sewing them down to the ends of the carbon tape. I then covered over those connections with this Silver Conductive Epoxy. 2.5 gm was plenty for the 4 connection points. I then added some additional strain relief at the connection points and wire entry point (at the heel) with some contact adhesive.
Step 3: Sew Insoles to Inside of a Pair of Fishing Socks
Grab a pair of appropriate fishing socks and turn them inside out. Sew your electric insoles to the bottom, with the carbon tape side against the sock. I used a pair of neoprene fishing socks, as they provide a bit of stiffness that I felt was desirable for electric socks (and maybe a bit of extra safety in case of a wader leak). The sewing here is tedious, since as far as I know it can only be done by hand. I used a blanket stitch around the perimeter, and made some extra passes at the wire entry to reinforce it. You might also consider stitching the wire to the top of the sock.
Turn the sock right side out and add connectors of your choice to the other ends of the wire. I used 2.1 x 5.5 mm male DC power plugs, as that is the connection to my portable 12V supply. A Y Connector then branches a single supply to the wires for each foot, which run down the inside of my wader legs. Don't forget to fuse the circuit for safety.
Step 4: Optional Variable Control
I have considered adding a controller in order to have variable power, but in my case that seems overly complicated given that my portable supply has a power button conveniently located along the edge, where it is easily accessible at the opening of my wader pocket.
If you want a variable control, there are plenty of off-the-shelf and DIY 12V PWM circuits on the web that can do the job.
You could even use a simple potentiometer, although turning down the heat would involve dumping some energy into the pot. For example, putting 3 Ohm in series (via a pot) would reduce the power to your feet to one half of max (8.4 V, 5 W per foot, 10 W total). The total current for both feet would then drop from 1.7 A to 1.2 A, and the amount of power being wasted in the pot would be 4.3 W. This would not be as efficient as using a PWM controller, but you'd still be saving some energy when you turn down the heat (14 W overall for half power to your feet vs. 20 W for full power to your feet).