My girlfriend often waits for a bus during 20-30 minutes. There is -5°C...-20°C sometimes. And today I want to show you my solution.

In the video you can see the test of this boots in beautiful New Year Helsinki.

Pleasant viewing :)

Step 1: I Used:

1) Wool Insoles like this:

http://s.click.aliexpress.com/e/ccScfELQ

2) Heating Nichrome Wire. I used 0.4mm:

http://s.click.aliexpress.com/e/jL1nvwo

3) Batteries Li-ion 18650:

http://s.click.aliexpress.com/e/bnXXyPtQ

4) Power Bank Case (5V, 1A):

http://s.click.aliexpress.com/e/zRJrt9q

5) Hand made USB powered cable for 5V, 1A.

6) Sewing Elastic Rubber 40mm:

http://s.click.aliexpress.com/e/bdAQtCMu

Step 2: Nichrome Wire.

I cut 65 cm of nichrome wire. It takes 5V, 0.7A for one foot. Insoles warm up to +49°С.

Step 3: USB-cable

I tested some USB-cables, but they could transfer only 0.5A unfortunately. And I made my own.

Step 4: Soles + Wire + USB-Cable

I sewed the wire and USB-cable to insoles. Nichrome wire couldn't solder, so i used needle with thread.

Step 5: Batteries

I used new li-ion batteries 18650. I tested it's capacity = 3400mAh! It's great :)

Let's calculate battery live time.

Battery has 3.7v and 3400 mAh, but Power Bank voltage transformer gives 5V.

So battery into case should has capacity: 3.7*3400/5 = 2516 mAh.

The nichrome wire "eat" 0.7A, so battery live time: 2516/700 = 3,6 hours. Voltage transformer efficiency, I think, 90%, so we have 3,6*0,9 = 3,24 hours.

It's about 3:15.

Will check it latter.

Step 6: Temperature Test

I got 21°C (without nichrome wire) and 49°C (with). Cool!

Step 7: Put Inside

Step 8: Strap

I sewed straps using 40mm rubber and velcro.

Step 9: Results

Hid under jeans :)

Step 10: Conclusion

We tested heated boots in Helsinki on the New Year holiday. It is a beautiful city! But it was so windy.

We were walking about 8 hours every day. And these boots were saving Masha.

Masha is happy. Me too :)

Live test showed they are great boots, don't causes discomfort. Live time about 2-3 hours. We didn't check the exact time.
But USB contact was bad. I want to change it to other connector type.

PS: Sorry for my bad English, I am still learning. You can correct me (please).

PSS: It's my first instruction, so I will be happy to read your opinions ;)