# Is it possible to make a pocket warmer from part of a hair dryer?

I have an old hair dryer and I know that there is something inside it which heats up the air. I was wondering, is it possible to remove that and attack a battery pack and case and have a pocket warmer or would it not work?

Thank you.

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5 years ago
In a hair-drier, the air is blown over a heated coil by the fan.

The heater coil is designed to run on 120/240V, so will probably not work too well on a lower voltage. Resistance wire is cheap, so it is far more practical to get some designed for your specific power supply.
iceng5 years ago
Put a 9V battery in your pocket add a few coins and voila,
you have a instant pocket warmer when a coin touches both contacts.
The battery can get quite hot after a minute or two.
I write from personal experience.

A

Jack A Lopez5 years ago
5 years ago
Or aluminum foil. Ha!

Jack A Lopez5 years ago
The idea is plausible, within certain constraints. I predict the two most significant problems with this idea are: (1) choosing a battery with sufficient energy density (2) matching that battery to your heating element.

Electrically speaking, the heating element is just a resistor, and the equations that model how it works are just Joule heating and Ohm's law, P=V*I and V=I*R respectively. I claim that most of the work that going into your pocket warmer design will be figuring out what size resistor, i.e. how many ohms, for your heating element. Also note you can substitute the second equation into the first to get P = V2/R  or P = I2*R . Because a battery is roughly like constant voltage source, the first of these, P = V2/R, will be more useful.

It may turn out that you want a resistance value for your heating element that is smaller or larger than the resistance of the element pulled out of your old hair dryer.

In the case you want a smaller resistor, note that the element in your hairdryer is just a length of nichrome wire.  You can make the resistance proportionally smaller, just by making the wire proportionally shorter, i.e. by cutting some of it off.
http://en.wikipedia.org/wiki/Heating_element
http://en.wikipedia.org/wiki/Nichrome

In the case that you want a larger resistor, you should just buy a resistor, because resistors are cheap.  The kind of resistor you want is probably going to be the "sandstone" style (it looks like a little ceramic box with sand glued into it), with a power rating of maybe 5 watts, or 10 watts, or whatever your power calculation (P = V2/R) says is necessary.

Note I have trouble imagining your battery powered hand warmer producing more than 10 W of heat, and having it still fit in your pocket. So I think that's a good rough estimate for power level, if you need a number to get started.

BTW, have you seen the ones that run on naphtha, or other chemical fuels...
http://en.wikipedia.org/wiki/Hand_warmer

KillerHoggle (author) 5 years ago
Ah, thank you all. What exactly is Resistance Wire, please?
Kiteman5 years ago
A pocket-sized battery will probably not provide enough juice to heat it up.