DIY heated insoles

Insoles with electric heating are a truly magnificent thing that will especially appeal to those who spend a lot of time outdoors in the winter, waiting for a bus at a bus stop or for other reasons. Really like this homemade fishermen or hunters.
Thanks to such comfortable insoles, you can warm your feet at any time and continue to warm them for 2-3 hours! What exactly will save you from a cold.

Will need

• The insoles are thick, made of wool or other material.
• Nichrome wire 0.4 mm in diameter.
• Li-ion rechargeable 18650 battery.
• The USB cable is two pieces, I think there are old gadgets in the household.
• Power Bank - housing for the battery with a USB connector.
• Elastic band for fastening.

Everything up to insoles can be ordered in China on Ali Express.

Making electric heated insoles

We take your shoes and insert insoles into it. We put on our feet, everything should sit well without undue pressure.
Unwind nichrome wire. I rewound 65 cm, the length is determined experimentally.
From 5 Volts this segment consumes 0.7 A of current. And it's all on one foot.
We make the USB plug, we bare and tin wires. We put a heat shrink on the plug so that the wire goes vertically down.
Now with this piece of nichrome wire we sew the central part of the insole. The heel is not involved, as it seemed to me that it is not necessary to warm it strongly.
You cannot solder a wire to a nichrome wire. To do this, it is simply wound on a USB prod and sewn with threads to the insole. Everything turned out pretty reliable.
Heated insoles are ready!

Some calculations

So, the battery has a capacity of 3400 mAh and a voltage of 3.7 V, the battery is original and corresponds to the declared parameter (personally checked). It is inserted into the power bank, in which there is a converter that increases the output voltage to 5 V. Therefore, the capacity will be less: 3.7 * 3400/5 = 2516 mAh.
The insole consumes 0.7 A from 5 V, therefore: 2516/700 = 3.6 hours. And given that the boost converter has an approximate efficiency of 90%, it will be: 3.6 * 0.9 = 3.24 hours.
As a result, at least 3 hours insole will warm its owner continuously! In my opinion this is an excellent result.

Test

We collect Power Bank, insert the battery.
We connect to the insoles and check, but first we measure the initial temperature and it was 21 degrees.
After a couple of minutes, the temperature rose to 49 degrees Celsius.
We put in shoes.
We output the USB cable. When walking, he does not interfere, he checked.
We sew fastening from an elastic plait.
Velcro is used as a lock for quick removal.
The finished clamp itself.
This is how it looks on the foot.
Nothing is noticeable.
In the same Ali Express, you can order ready-made insoles with heating, so if you are too lazy to bother - just buy it.

Watch a video

Original article in English