# How to heat nichrome wire with home batteries at 37C (99F) degrees

## Main Question or Discussion Point

Hello,

I would like to be able to heat a nichrome wire with batteries (probably with a D batterie, but if it can be done with AA batteries, it's better, cause it's cheaper).

I would like to be able to heat a nichrome wire of about 2 feat long at a temperature similar to the body temperature (99F or 37C) for at least 2 hours. For the nichrome wire, thinner is better (more flexible).

Eventually I will try to put this in my winter boots and see if it can keep my feet warm. I know heating socks already exist, but I want to try to build my own.

So:
- what specs should my nichrome wire have
- what would be the best batterie for this, and how many do I need
- what should I change to keep the same wire temperature, if I change the length of the my wire to 1 foot or 3 feet.

Hope I being clear.

Thank you.

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Hello,

I would like to be able to heat a nichrome wire with batteries (probably with a D batterie, but if it can be done with AA batteries, it's better, cause it's cheaper).

I would like to be able to heat a nichrome wire of about 2 feat long at a temperature similar to the body temperature (99F or 37C) for at least 2 hours. For the nichrome wire, thinner is better (more flexible).

Eventually I will try to put this in my winter boots and see if it can keep my feet warm. I know heating socks already exist, but I want to try to build my own...
Hello provma 79,

This is potentially very dangerous, please do not try it, as you could get badly burned if things go wrong.

vk6kro
You would need to guess a bit with this.

Suppose R1 and R2 (the heaters for each boot) needed 6 watts each to produce reasonable warming.
Power = voltage * current
so current = 6 watts / 6 volts = 1 amp per boot.

Resistance = Voltage / current = 6 volts / 1 amp = 6 ohms.

Now, if you look at this table:
from :http://www.wiretron.com/nicrdat.html [Broken]

you can use about 3 ft of 25 AWG Nichrome or 2 ft of 27 AWG Nichrome per boot to get 6 ohms.

You need 2 amps for 2 hours so that is 4 amp-hours. That would mean you would need rechargeable NiMH D cells or maybe a 6 volt lead acid motor cycle battery.

I support the safety warning given by Adjuster and hope you would make sure it is safe before you put your feet into something like this. You would have to put the Nichrome wire in a suitable insulator so that it does not touch your feet.

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provma79, a student came to one of our IEEE club meetings on tuesday and asked the very same question. Look up thermistors, and you might want to also research pulse with modulation. I agree with everyone elses warning, you should be very careful if you build your circuit. A simple resistive circuit would be much easier to build but it would not be safer.