i need heated clothing. i don't need to spend a pile of money on it.. so this is my thread detailing what i've learned and how i plan to do this.
disclaimer - i might be an engineer, but i take zero responsibility for anything you try on your own.. be careful!
it gets kind of cold here in atlanta. sometimes it dips into the teens and even single digits, but we typically have quite a few sub 30* days and many in the 20s, especially in january and early february.
i haven't added anything to my bike yet so i figured heated clothing is a good place to start. it's functional and will hopefully help me get over this "riding season" concept and become a 12 month rider.
seeing that heated jackets cost $200 or so and gloves cost $150 or so i thought there had to be a better way. so i started research.
there's little in this world that's really "new" so i have to give credit to the sites i found via google that have been there before me. i'm not breaking new ground here, rather chronicling my experience of design, material selection and, once it all gets here, the installation and testing of the gear.
electrical energy can be used in a few different ways, among them being production of light, work, and heat. we're going for heat, so the idea is pretty darn simple.
heating elements result from a controlled short circuit. if you pass current through anything with resistance (and everything has it short of a superconductor) then heat is a byproduct.
how do we figure out how to make this happen? heat output is typically measured in BTUs. we don't talk in BTUs for this equation, however, because it's easier to do it based on watts. it makes more sense and is easier to compare to the name brand products out there. i'll skip all the BTU stuff and you can google it if you're interested.
watts = volts x amps
since our bikes run on a 12v system, we can calculate how many amps we need to use to produce a certain amount of heat.
amps = volts / resistance (this is called Ohm's law)
using these two equations we can figure out how many feet of heating element we need to put in our clothing to get the desired amount of heat. voltage is constant, so the resistance is the variable we manipulate in order to get the desired amount of output (wattage).
based on what i've read, and on others' successful experiences, i chose 30awg teflon coated stranded copper wire. it's very thin, flexible and the PTFE (teflon) jacketing adds to its durability and heat resistance. basically you aren't going to melt the wire insulation off and stick it to your skin...
the next step is to measure the resistance of the wire you have. MAKE SURE IT IS UNCOILED!!! measuring the resistance of a coil of wire will not give you a true reading due to induction. you need a ACCURATE ohms/ft reading in order to make this work. don't use the published specified ohms/ft the manufacturer gives you.. measure it yourself.
once you determine how many watts of heat you want, do the math. you'll know how many amps you need to draw to accomplish that. then, using the Ohm's law equation, you can figure out how many ohms of resistance you need to make it work. divide that amount by the ohms/ft reading you took and you know how many feet of wire you need to use in your heated gear.
NOTE - i just bought my materials today and am waiting for them to ship. i'll cover this in greater detail in a reply to this post once i have everything and do this myself.
CONTROL OF THE HEAT
the easiest way to accomplish this is an on/off switch. it's the cheapest too, but not by much as you'll see in a little bit.
most of the big companies sell adjustable heat controllers. you can use one of theirs or you can source your own.
the concept of pulse wave modulation is what's used in many industrial applications to control motor speeds. a circuit is used to switch power on and off in rapid fire. by adjusting the duration of these pulses you get the desired outcome - a slower or faster spinning motor, or MORE/LESS heat.
through another DIY site i found a PWM circuit that is rated for 15 amps (WAY more than i need) at 12v. this will give me a knob with 0%-100% adjustment in the heat output. pretty slick.
HOOK IT UP
this is one area where you can't beat the factory stuff. i'll be using a factory made battery harness to hook the power up.
for all the interconnections between the jacket and bike and jacket/gloves i'm using SAE 2 pole flat connectors similar to what gerbings used to employ in their design. they've since gone to size N coaxial DC power plugs but i don't want to go that route.. harder to find parts, more expensive for good stuff, less mad max looking
RESOURCES FOR PURCHASING ALL THIS CRAP
here's what i bought and where i bought it:
30awg PTFE jacketed wire - 100' spool (i dont need this much.. but hey, i can heat some other gear later
) - $31-ish
vehicle connection (battery whip w/fuse) - warmgear brand - $7.95
note - they also sell a trick factory made in line switch if you don't want to do a PWM controller..
PWM controller - quality kits - $18.95
i found the 2 pole SAE flat connectors at my local hardware store for $2.29 each. i bought 5 "jumper" style connectors that i plan to cut up giving me a total of 10 SAE plugs. (planning to make it so I can do gloves only as opposed to requiring use of the jacket to get the toasty fingers..)
misc stuff like heatshrink tubing and solder already exist in my shop. i'll need to source a box and knob for the PWM controller. i'll hit up the local radio nerd store for that. i'll probably add a master on/off disconnect switch in that box as well. maybe a status LED also. we'll see how impatient i get..
what's the next step? i'm waiting on everything to get here so i can get a reading on the wire. then i'll determine the length of cable i need to use, and then i'll be stitching the wire into my jacket and glove liners. once that's complete i'll install everything and test it out.
wish me luck and fire away with any questions. i'll be taking a ton of pictures as i go through the process.