DIY heated clothing

Step 2 Theory

You can skip this part if you don't want to know any of this.

This works on the same principal as a light bulb or a toaster.  Pass electricity through a high resistance, and you get heat.  In this case though, we are controlling how much heat the clothing will put out by varying the length of wire we will use.  To figure out how much wire to use, we will use ohm's law or

Current [Amps] = Voltage [Volts] divided by Resistance [Ohms]

The wire we are using has a resistance of .1 ohms per foot.  So if we used 30 feet of wire, the total resistance would be 3 ohms.  This is ignoring the resistance of the connectors and wire going to the battery but it should be negligible in our calculations. The voltage of most modern motorcycle batteries is 12 volts.  So 12V/ 3 ohms = 4 amps.  Now we know how much current our pants will draw. 

So you want to know how hot this will be? Here's an excerpt from this site

Power [Watts] = Current [Amps] x Voltage [Volts]

Based on our project consisting of a 12-volt battery and a current of 4-amps, the power consumption would be (4-amps x 12-volts = ) 48-watts.  The heat output of 48-watts, can be expressed in British Thermal Units (BTU) per hour by performing the following conversion:

BTU / Hour = Watts x 3.413

Put simply, one British Thermal Unit (BTU) is the amount of heat required to raise the temperature of 1-pound ( lb) of water 1-degree Fahrenheit.  Thus the vest in our project would output ( 48-watts x 3.413 = ) approximately 164 BTUs per hour.  If this value isn't intuitive to you, consider that 48-watts is similar to a 50-watt light bulb, and imagine the amount of heat that a 50-watt light bulb outputs.  That may not sound like much, but when that amount of heat is contained under a jacket, you will find that it is plenty warm.

Also, if you were to look at the power output of Gerbing's heated pants, you'll see that they put out 44 watts of energy, so our pants will be warmer than theirs.  If you want to go even hotter than that, just use a shorter length of wire.  Just remember ohm's law and you'll be all set.

Comments

[slomak]

Hope this question is not too elementary (electronics is not my forte), but I was wondering how to draw heat through resistance wire and not fry the battery. I've taken 2 AA batteries with leads, connected resistance wire (10" length) to both leads to complete a circuit. Got plenty of response and then essentially a dead battery. / If I used more wire (10') would that keep the battery from frying, while still producing heat? Otherwise, how do you draw significant current through the wire without killing the battery?? Thanks for any advice.

[vze1mk7d]

AA batteries are not really meant for high amperage circuits. And their capacity is usually on the smaller side and it won't take much to drain them. I'm not sure what your circuit is but try using more wire and a battery meant for high drain applications.

[slim_jim]

9 volts? It's not the volts, it's the amps. That's like asking if a 1 inch wide garden hose will reach the back yard. Wrong measurement. But to answer your question, no way in hell would a standard 9 volt battery work. (The regular kind, like in a smoke detector. Sometimes called a transistorized battery. It wouldn't power these pants for more than a second.) Now, if you have a big gel cell 9volt battery, sure. No problem.

Heating circuits are hell on batteries. Tons of current drain. You will need a decent sized battery.

[DehLeprechaun]

i want to use this just for walking around out side could i hook up a 9v battery and get similar results?