How To Make Electric Heated Clothing
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If you have contemplated riding in cold weather, I'm sure you are familiar with the electric vests, pants, chaps, gloves, etc. on the market. You also know that these items tend to be a little pricy. You may be surprised to find out that these items are extremely easy and cheap to make. This article describes how to make an electric vest, but as you will see, the method and principles can be applied to just about any clothing item you can think of. The best part is that it will only cost you a little time, and a fraction of the money that stores are charging for similar pieces of clothing. Additionally, you can customize your clothing to meet your needs and make it much more durable than some of the retail models. Having built your own electric clothing, you will also be a master at repairing it, which could be priceless knowledge when your electric vest stops working in a snowstorm north of the Arctic Circle. Lastly, when you pull up next to other riders who have "BMW Motorad" or "Harley Davidson" imprinted several times on every piece of clothing that they are wearing, you will be able to laugh knowing that you spent a fraction of the money they did, and were badass enough to make your own useful and functional clothing.
So how long is long enough? This is governed by Ohm's Law that states:
Current [Amps] = Voltage [Volts] divided by Resistance [Ohms]
Assuming you are making electric clothing for a modern motorcycle, your voltage is controlled by your battery, which is most likely 12-volts. The resistance will be governed by the length of wire, connection, and switches that you use in the circuit that connects the battery terminals. Wire manufactures usually specify the amount of resistance (in 'ohms') per foot of wire. Likewise, every switch and connection will have some resistance associated with it. Resistance may also be measured with a basic electric multi-meter, which will give you the actual measured resistance as opposed to the "if everything is perfect" manufacturer's specified resistance. For this project we are going to use wire that has a resistance of 0.1-ohms per linear foot. Assuming that we use 30-feet of this wire, our total resistance will be (0.1-ohms per foot x 30-feet =) 3-ohms. Keep in mind that the total resistance will also include the resistance of any switches and connections, although these are usually minor compared to the resistance of the wire in this case. Using Ohm's Law, the total approximate drain on our battery will be:
Current [amps] = 12-volts / 3-ohms
Current [amps] = 4-amps
This information is useful since it dictates the size of the fuse that must be used in the circuit. In this case, if you are installing an in-line fuse, your fuse must be larger than 4-amps. If you are connecting to an existing power outlet on your motorcycle (i.e. BMW PowerLet), you must ensure that the fuse protecting the outlet can handle the current required by your electric clothing.
Notice that the less resistance the wire has, the more current will be drawn from the power source, resulting in more heat. This could be accomplished by simply using a shorter wire.
So how "hot" is 4-amps? To calculate how much heat the electric clothing will generate, we need a couple additional formulas. First, calculate the power required by the vest in Watts:
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.
So now that you have earned your Associate's Degree in Electrical Engineering, you are ready to build your electric clothing. The important thing to remember is that less resistance (i.e. shorter wire), means hotter clothing, and a larger draw on your battery. Also, keep in mind that a larger draw on your battery means a larger toll on your motorcycle's recharging system.
Based on your calculations of resistance, current, and heat output, you basically have the specifications for the type of wire you should use in your clothing. Based on experience, I have found that 30-gage, stranded copper, Teflon coated wire works the best for a few reasons. First, the wire is extremely small, permitting it to literally be sewn into the garment you are electrifying. Second, the wire is extremely flexible (since it is stranded, and NOT solid) and durable for its size. Third, the wire can function under extreme heat (200-degrees Celsius), making it ideal for heating applications. Odds are, you won't find this wire at your local Radio Shack. It is readily available from several suppliers on the web for approximately $15 to $20 per 100-feet (enough to make three articles of electrified clothing). Just do a web search for "30 AWG stranded Teflon coated copper wire". Be sure to order stranded wire since the same wire is also available in solid copper.
Next you need to consider a connection between the fine 30-gage wire and the smaller gage power source wire. Also consider if you want to have a long wire always hanging from your vest (clothing), or if you want to just have a small pigtail, so that you can wear the vest away from your bike without looking like a dweeb. The method I describe in this article entails creating a removable extension cord between your power outlet and your clothing. Other things to consider are a switch, so that you can simply turn your clothing on and off without having to unplug it, and a multi-temperature control. A rare few of the more-expensive retail vests offer this feature. Later in this article I will describe how you can easily add this feature for only a few extra bucks, and a little extra time.
Lastly, you need to consider what you are going to electrify. The most popular choice is a vest, but just about any piece of clothing can be electrified. I have found that polyester fleece items work the best since you can sew the heating wire to the inside of the garment without having the wire exposed on the outside of the garment. Keep in mind that an appropriate material should be selected such that it is not damaged by the heat output from the wiring.
The following is the list of materials that I used to construct the vest in this example:
Installing Heating Wire
in the Clothing
After you have the string laid along the future path of the heating wire, either tack it in place or lightly trace it with a piece of chalk.
Note: This example is for running a single, continuous length of heating wire. You can also easily make a multi-temperature piece of electric clothing by running a few different lengths of wire throughout your clothing. As described above, different lengths of wire will result in different resistivity and thus different heat outputs. You can connect each length of wire to a different plug (connection), or to a multi-way switch, permitting you to change which wire, and resulting heat output, is used in the clothing.
If you are using the wire mentioned in this example, you should be able to thread it through a large needle and sew it along the pre-planned path using large stitches. Be careful not to crimp or break the wire as you pull it through the garment, since the wire must be continuous and is a pain to repair due to its small size. I found that pulling the entire length of wire through at the end of each "row" of straight section of stitching makes it much easier to manage. Remember that in this case we are working with 30-feet of wire. Obviously the wire gets easier to manage as you get more of it sewn into the garment.
To construct the electrical connection on the vest, I cut one end of the coiled microphone cord, including about two full coils. The 4-wire microphone wire has four wires (yellow, black, red, white) and a bare shielding wire. Obviously you do not want the extension cord to dissipate heat since it will just be flopping in the air as you ride. To reduce the amount of heat dissipated by the extension cord, we must decrease it resistance which may be accomplished by using a smaller gage (larger diameter wire). I accomplished this using the 4-wire microphone wire by combining its 4-wires and shielding wire into two wires (e.g. I connected the red, black, and white wires together, and connected the shielding wire and yellow wire together). On the coiled end of the cut piece of microphone wire, strip about 3/4 of an inch of the outer sheath, combine the wires as described, and then strip and connect each end of the heating wire to the microphone wire. I found that stripping about 1-inch on each end of the heating wire and then twisting this around each respective end of the (combined) microphone wire, and then soldering each connection worked very well. Be careful not to crimp the heating wire while stripping it, since any crimp will act as a potential breaking point. After you have soldered the connections, use electrical tape to help insulate them, or for more durability, use wire-shrink. On the opposite end of this wire, connect a MALE mono stereo plug.
IMPORTANT: It is important to use a MALE connection on the garment and FEMALE connection on the extension cord, since if the garment is disconnected from the extension cord, and the cord drops and contacts a metal portion of the bike, it may short-circuit and blow a fuse since the other end of the extension cord would still be connected to the power source. This would happen since a male plug leaves the live anode exposed. By using a FEMALE plug on the extension cord, the live anode is shielded, and thus there is little danger of causing a short-circuit.
The purpose of leaving two full coils on this pigtail connection will become obvious as you anchor the pigtail to the garment. The anchoring of the pigtail is accomplished by using about 4-inches of shoelace. Cut two small slits, about half an inch apart in the garment; preferably on either side of an existing seam. Lace the short shoelace part through these slits and then through the coils on the pigtail and tie the shoelace into a permanent knot. The picture at left shows this on a vest. Note that this vest has two such pigtails, each connected to a different length of heating wire that is stitched throughout the vest, providing two temperature options.
At this point, if you own an electric multi-meter, I would recommend testing the resistance of the heating wire and pigtail connection. This will give you an idea of the electrical draw and heating capabilities of your garment (using the previously mentioned equations), as well as indicating if you have a closed circuit (i.e. no broken wires). Once you are confident that your heating wire and pigtail connection are adequately anchored, you may want to line the garment with a thin piece of cotton material. This will serve to protect your wiring, as well as reduce the likelihood of the heating wire burning your clothes or skin due to direct contact.
To construct the extension cord, use the remainder of the coiled microphone cord. You may need to cut it to length (or possibly use a new, longer cord) depending on the location of the power source. Strip and combine the wires on both ends of the coiled cord in the exact same order as on the garment's pigtail connection. On one end of the coiled cord, connect a FEMALE mono stereo plug. On the other end, connect a BMW PowerLet socket or other type of socket/ connection that is compatible with your power source.
Heat controllers are in essence electrical circuits that turn your electrical clothing on and off at a very fast rate. Averaged over time, and depending on the setting of the heat controller circuit, your electrical clothing will be 'turned off' for a percentage of time, causing it to pull less power, and thus not heat up as much as if it were receiving power 100% of the time.
I highly recommend visiting http://www.hwy2hell.net/3000.html for an excellent solution for building your own heat controller.
Using a Portable Battery as a Power Source
How long a battery (not being continuously recharged, as in your motorcycle) will last while powering your heating clothing depends on several factors, the most significant of which are:
Being that you have already earned your Associate's Degree in Electrical Engineering earlier in this article, you now how to calculate the amperage required by your heated clothing, so the next step is to take a look at the battery you are planning on using as a power source.
The most common battery rating is the 'amp-hour' rating. This is a unit of measurement for battery's capacity, calculated by multiplying a current (in amps) by the time (in hours) of discharge. For example, a battery which delivers 5 amps for 20 hours delivers 5 amps x 20 hours =100 amp-hours. However, as a word of caution, manufacturers use different discharge periods when specifying amp-hour ratings for the same capacity batteries, therefore, the amp-hour rating has little significance unless qualified by the number of hours the battery is discharged. For this reason amp-hour ratings are only a general method of evaluating a battery's capacity for selection purposes. The quality of the materials and construction of the battery will generate different desired characteristics without effecting its amp-hour rating. For example, there are 100 amp-hour batteries that will not support an electrical load overnight, and will typically fail early in their life if used to do so on a frequent basis. Conversely, there are 100 amp-hour batteries that will operate an electrical load for several days before needing recharging and will do so for years. Furthermore, the amp-hour rating is only valid at a certain ambient air temperature. The colder it gets, the lower the amp-hour rating becomes.
A typical motorcycle battery may have an amp-hour rating of somewhere in the range of 10 to 20 amp-hours. For this example, we will assume our battery has a 15 amp-hour rating and that our heated vest is drawing 4 amps (as calculated above). So how long could we expect our battery (not being recharged) to last when used to power our heated vest? A general rule is to divide the battery's amp-hour rating by two (2) times the amperage of your heated clothing. However, the answer should be considered the maximum amount of time that your battery will last under perfect conditions, which of course never occur. To answer the question in our example:
(Battery Rating [amp-hours]) / (2 x Heating Clothing Amperage [amps]) =
(15 amp-hours) / (2 x 4 amps) =
(15 amp-hours) / (8 amps) = 1.9 hours
Remember that this is the amount of time the battery would last under 'perfect conditions' - so basically, don't count on it.
As mentioned above, temperature plays a huge role in how long your battery last. Batteries lose more of their charge as the ambient temperature gets colder. The lower the temperature, the shorter time a battery will provide power for your heated clothing. Ironically, you obviously only need your heated clothing in cold temperatures, so these two facts work against you. In our example, sitting at a football game in 30-degree weather, drinking cold beer, with your 4 amp heated vest and 15 amp-hour motorcycle battery as a power source, you may be lucky to get a half hour to forty minutes of heat from your vest. The solution? Drink your beer fast!
This article should be considered a work-in-progress. If you find any errors, discover an easier or better way of doing something, or just have a unique idea or twist on the construction of electric clothing, I encourage you to submit the information for inclusion in this article. Credit will be provided within the document to those individuals submitting such information (unless otherwise requested). Please submit any comments, questions, or additional information to MotoTour. This article will always be provided to the public free-of-charge on our site.
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