Mod Your Clothes (part 1)
I'm seriously sick of winter. You either spend half an hour putting on 7 layers of clothing to go outside or you spend an hour freezing because the bus was late. The cheapest commercially available electrically heated jacket that I know of costs like $300, which I think is just plain stupid for a bunch of wire and a battery. In part 1 of this project, I will show you how to mod your existing clothes so that they can be electrically heated. If you have a laptop, you can actually pull this off completely for free! :)
So some theory first: An electric heater is basically a lot
of electricity running through a wire to produce heat. To make a wire heat
up, just apply a voltage across it. So to make a portable heater, you just
need a battery, and some wire wrapped around whatever you want to heat.
But how will you ensure you don' t make the wire so damn hot it melts? How will you ensure you get enough heat generated for the mod to be useful? How will you ensure that your battery doesn't explode because you are drawing too much current? For EE n00bs, the two equations that are your friends in this mod are Volts = Current * Resistance, and Power = (Volts²) / Resistance. (V=IR and P=V²/R from now on).
Let's say you have a 12v laptop battery that normally delivers 40W of power to your laptop. To make a 40W heater using this battery, you must choose wire of a certain resistance. From P=V²/R: 40=12²/R. Solving the equation tells you that you want a wire with 3.6 ohms of resistance to do the job. To get a wire of that much resistance, you've gotta find some pretty thin stuff. Forget about the good quality thick wires you connect your speaker system up with- they have almost 0 resistance. If you connect that stuff across your battery its going to blow up. Find a roll of the thinnest wire you can that is reasonably strong and isn't so stupidly thin its gonna melt just by farting on it. Now whip out your multimeter and cut the wire at whatever length gives 3.6ohms resistance. Now just connect this wire across your battery terminals, and you should instantly feel the wire heating up quite a lot.
Pretty picture time!
Here is how I got my wire. I found an old fan in a power supply
in a dump. I ripped it apart.
I broke some stuff, then I unravelled the coil wire from the fan onto an empty
bottle. This electromagnetic coil wire is great. It is really thin, bendy,
strong, and its completely insulated so it doesn't matter if it crosses over
itself when you are sewing it into your clothes. And if it starts to rain,
you wont get electrocuted! If you aren't able to get this wire from radio
shack or whatever, 1 fan should give you enough wire to mod an entire wardrobe.
I cut about 5m of wire just for the hell of it, and measured the resistance.
About 3.5 ohms. With a little 9v battery you should get a 23W heater (assuming
the battery can deliver enough current. (Which it can't)). I threaded needles
onto both ends of the wire.
My unmodded jacket.
I decided to start the sewing near a pocket because I can easily fit a battery
and a switch in there.
I turned a sleeve of the jacket inside out, and just sewed wire into it. Then
I inverted the sleeve again.
I used my teeth to strip some of the insulation off the wires then I connected
a 9v battery to both ends. Things got nice and hot.
With a fresh battery, it felt like fire was running down my arm or something
it was damn cool. But these little 9v batteries suck. After less than a minute,
no more heat was getting produced. The battery was still giving 8+ volts,
so obviously it wasn't able to supply enough current (by I=V/R, it had to
supply 9/3.5 = 2.57 amps). Im guessing this is because putting such a huge
load on the battery suddenly causes lots of gas bubbles to form around one
of the electrodes which fuxors things up until you disconnect and leave it
to dissipate the gas.
So yeah, this is just the basic idea of the project. I just won a cool Li-ion battery/charger on ebay and once I get that I will sew wire all throughout my jacket and see how things go. Also, when I stick my arm into the sleeve of the jacket my fingers get tangled up on the wires. So next time I will re-sew everything so that the wires go inside the jacket lining instead. Laptop users can just charge up their batteries as normal overnight, then use the battery to heat themselves when they go to class, then put the battery back in the laptop once they get inside and start downloading pr0n over 802.11b during lectures.