Introduction: 12V Electric Socks for Float Tube / Pontoon Boat

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).

Comments

author
tomatoskins (author)2015-05-01

What a great idea! Have you measured how hot your socks get?

author
magnus99 (author)tomatoskins2015-05-01

Great question. I only have a long answer for now, explaining my guesstimate, as I finished these just in time to not need them for spring fishing (the local surface temp has now exceeded 50 degF). If I can get my hands on a remote temperature probe I will measure my foot temp in cold water this Fall / Winter and post the results.

The temperature will of course depend on the temperature of the surrounding environment. Not knowing the wattage I needed, I took note of this product:

http://www.amazon.com/Firstgear-Heated-MEDIUM-Moto...

which uses 9W per foot. Notice that some of the reviewers state they are simply too warm for motorcyle riding without a controller (which they are supposed to purchase with them). But I figured perhaps 9 W wouldn't be too warm for water temps that are just over freezing.

The manufacturer lists the temp that the carbon fiber will reach in an "ambient" environment of 73 degF. If I use my measured 14 Ohms and find a matching current in their data tables (instead of their posted length) it tells me to expect about 141 degF for my design. If I translate that down to an ambient temperature of, say, 40 degF, I get 108 degF, although I kinda doubt it is that simple. This does tell me, however, that I can probably expect to have to cycle them off, which is no big deal.

Not sure how I got so far off (14 Ohms vs. 19 Ohms), since I thought I cut out a meter length. Perhaps I simply cut the length that fit my insole - I don't actually remember. Silly me, I should have measured the resistance to the cut point before making the cut, but I'm not sure I could have fit much more anyway. I also intend to make a current probe adapter so that I can measure the actual current draw. The 14 Ohms was measured with a multimeter, and it is possible that the resistance changes when it is carrying a meaningful current. I do know that the resistance of graphite resistors goes down with temperature, so I unfortunately don't expect it to be in the direction I would prefer. In the end, however, I don't think having them warmer than expected represents a problem as long as I can easily cycle the power and have enough battery lifetime for an outing.

I have had them on in the house, and I can say they are too warm to leave on continuously for that application. :-)

author
Shenzhen (author)magnus992015-05-03

Resistance of tape is different in various shipments. Resistance of your
tape is 16.9 ohm / m. Experimentally we found no change in the resistance
of the carbon tape when heated from 25 to 300 degrees Celsius.

Of course, you're right, a comfortable temperature dependent on the ambient temperature, air or water using, speed of wind or water, our metabolism and physical activity. In my opinion it's good if you have excess power (temperature) and a controller to set the desired temperature.

author
magnus99 (author)Shenzhen2015-05-03

Thank you. Note that the datasheet on the website says 19 +/- 1 Ohm / m (so 18-20 Ohm / m). Maybe that spec needs a bit of tuning. I agree that having excess power available is much better than not having enough. :-)

author
Shenzhen (author)magnus992015-05-03

Thank you I've asked to change.

author
tomatoskins (author)magnus992015-05-02

Great explanation! I love it!

author
Shenzhen (author)2015-05-02

The author has just received a prize of $ 200 for this project:

http://carbonheater.us/

Well done!

author
magnus99 (author)Shenzhen2015-05-02

Thank you! Your carbon fiber tape is a great product.

author
Meganandjack (author)2015-05-02

in a boat what if water gets in the boat ? Then you get electrocuted .

author

Not really. It's all about the amperage and electricity's desire to find the least resistant path back to ground. In this case, ground is the negative terminal on the battery. Think about birds on power lines. They don't get fried because the electricity has nowhere to go to through their bodies.

author
magnus99 (author)john.grimoldy2015-05-02

OK, sorry, I can't resist. Small birds don't get fried on a power line, but large birds can get a shock. This, however, is the result of power lines carrying AC. AC current can flow in and out of a capacitor without a closed path to ground. So if the capacitance of their body is high enough, birds can get a shock, as can you, from grabbing onto a HV line. I recall going through an exercise in an undergraduate EE power class to estimate the size a bird has to be before it receives an uncomfortable jolt. Anyway, I'm told this is why large birds don't perch on power lines. :-)

author
magnus99 (author)Meganandjack2015-05-02

The worry for me is if water gets in my waders, and the foot area is unfortunately usually the first point of failure for waders (other than climbing over barbed wire fences, that is). I'm not worried about getting electrocuted but am worried about stressing my battery, especially in salt water. Lithium ion batteries are supposed to be protected from external short circuits (their dangers stem from internal shorts), but why take a chance? This is why advise that you fuse your battery connection to the socks. It's easy to add a 3A micro blade fuse. I am adding that to the Y connector that I show.

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