Will this wire burn me or melt my clothes ?

[DrAlloway]

Will this wire burn me or melt my clothes ??

I am making a heated motorcycle jacket - so 13 volts DC (actual measurement while riding).

For heating wire I am using 30 gauge (7 strand x 40 AWG) tinned copper wire with Teflon insulation (good to 250C) which has a resistance of 0.102 ohms per foot (actual measurement as versus 0.103 from tables).

I will sew 22 feet of this wire into my jacket so that gives me:
2.24 ohms, 5.8 amps, and 75 watts.

75 watts over 22 feet is 3.43 watts per foot.

The practical question is will this wire burn me or melt my polyester jacket ??

I do Not need the exact temperature of this wire. There are no second or third degree issues as the wire is sewn into polyester insulation between my jacket shell and liner. So there is NO air circulation, fan, or any complications.

There must be a formula for calculating the APPROXIMATE temperature of this wire.

Any help will be greatly appreciated as I am definitely not an electrical engineer.

thanks, Bob

 

[russ_watters]

You can always test it first (coil the wire up in a blanket), but no, it sounds just about right. Here's an ad for an electric blanket at 102 watts: http://www.electricblanket.net/p-14-safe-low-voltage-electric-blanket.aspx

Cool project (pun sort of intended).

 

[DrAlloway]

I don't have a source of 13 volt power unless I am riding my bike down the road.

The wire will be spread evenly throughout my jacket - so coiling it up isn't a good test - although that would give me a max worse case.

The 102 watt blanket is a good example, but I don't know how many feet of wire they are using - so the temperature per foot could be quite different. But it is a good example because there is no air circulation in the blanket. I remember using one of these somewhere and that the High setting was too hot. Of course, I will be riding at 70mph in 40F weather, so that should cool my jacket more than an electric blanket on a bed.

 

[MATLABdude]

I don't have a source of 13 volt power unless I am riding my bike down the road.

The wire will be spread evenly throughout my jacket - so coiling it up isn't a good test - although that would give me a max worse case.

The 102 watt blanket is a good example, but I don't know how many feet of wire they are using - so the temperature per foot could be quite different. But it is a good example because there is no air circulation in the blanket. I remember using one of these somewhere and that the High setting was too hot. Of course, I will be riding at 70mph in 40F weather, so that should cool my jacket more than an electric blanket on a bed.

If you have a car battery, that'd be able to supply close to 13V at sufficient current for long enough to determine whether or not it gets uncomfortably hot. Also, I'm assuming you're sewing in something so that it'll help diffuse the heat a little? Not so much that you lose more heat to the outside than gets put into you, but something to diffuse it a tad (the difference between a 40 W soldering iron applied to you, and a 40 W electric blanket applied to you).

EDIT: That's not only a neato idea, but also customizable: if you find the jacket is too hot, you can add some more wiring, and you can cut it down to do the opposite!

 

[DrAlloway]

OK, with my bike at idle, the battery will be sufficient to test how hot this wire gets. I have a 16 foot test piece of 32 gauge wire I can just plug in and wait a few minutes check it with a thermometer.

Still there ought to be a formula I can use in my spreadsheet to help me do the design.

The heat is spread around because the wire is sewn evenly throughout the jacket.

My current Jacket design has 4 parallel loops of wire:
Loop 1 is 14 feet of 30 gauge
Loop 2 is 22 feet of 30 gauge
Loop 3 is 30 feet of 32 gauge
Loop 4 is 48 feet of 32 gauge
The Gloves will have 7 feet each of 32 gauge and be in Series together.

The plan is to be able to plug the Gloves into any Loop 1 to 4 and get 4 to 28 watts of heat.
Then plug in any additional Loops to add more heat to the Jacket - with the combinations I will be able to get just about any heat level I need for the weather.

 

[dlgoff]

Still there ought to be a formula I can use in my spreadsheet to help me do the design.

Here is a thread on this: https://www.physicsforums.com/showthread.php?t=280251"

 

[DrAlloway]

I followed the suggested thread - it basically says its way too complicated - at least the example in that thread.

My application is simplified - ie - the wire is sewn into the polyester insulation in my jacket. So there is NO air circulation or heat sink to carry off the heat.

These variables are known:
13 volts DC
22 feet of 30 gauge stranded & tinned copper wire
2.34 ohms of resistance
5.8 amps of current
75 watts

So I have started trying the experimental approach - because all you guys keep saying this problem is way to complicated for humans.

I have a 12 volt, 3 amp battery charger.
I hooked up a 16 foot, 32 gauge stranded & tinned copper wire
resistance of this wire is 145 ohms per thousand feet
this wire should draw 5.17 amps

It got hot to the touch but you could hold it.
I wrapped it around a thermometer and I think it maxed my human thermometer at 108F

The battery charger has some sort of safety circuit in it and it keeps popping - so maybe this wire is drawing more than 3 amps (as it should if it was available)

So now I have a secondary question - will a 12 v, 3 amp battery charger put out more amps it the draw is there - and pop the battery charger's safety circuit ??

AND ?? also pop the fuse on my 10 amp ammeter ??

 

[russ_watters]

Yes, a power supply puts out as much power as the load draws or fails trying.

 

[Homer Simpson]

why don't you just wire in a potentiometer to vary the voltage... an easy way to dial down the heat if it's a bit much.

 

[DrAlloway]

Yes, a power supply puts out as much power as the load draws or fails trying.

Apparently - my ammeter read 14.78 before I could pull the plug - and I was ready with my hand on the wire.
The battery charger says 3 amps in big letters right on it.
Apparently this means 3 amps until it thinks about poping its safety/overload circuit.

So when I have my 16 feet of 32 gauge test wire attached to the battery charger - how in the world can I measure what amps are really being drawn ?? If I put my ammeter on the circuit (it will then be in parallel with my test wire) ?? it will just draw lots of amps instead of reading what amps are being drawn by the wire ?? if that is the case what good is an ammeter ??

 

[DrAlloway]

why don't you just wire in a potentiometer to vary the voltage... an easy way to dial down the heat if it's a bit much.

Motorcycles only generate a limited amount of juice (mine is 300 watts or 25 amps) and it takes 100 to 150 watts for all the lights, turn signals, etc. So in my heated clothing design I have limited myself to 150 watts (jacket, gloves, pants, socks).

If I only need 1/2 power for heating on a particular day - a potentiometer will still draw 150 watts instead of 75 watts. I would rather turn on my running lights (70 watts total) than waste watts in a potentiometer.

 

[DrAlloway]

OK, so I guess I am making progress using my battery charger

I cut a 32 foot piece of 32 gauge wire
with 0.145 ohms per foot
so 4.64 ohms
11.94 volts from battery charger
2.57 amps
30.7 watts
0.96 watts per linear foot

Measured temperature (I wraped wire 6 times around bulb on thermometer and then held coil in place with my finger and thumb) was:
107.4 F

I think this worked because the wire only draws 2.57 amps which is less than 3 amps the battery charger is happy putting out.

To my way of thinking the measured 107.4 is higher than it would be in actual operation because:
when wire is sewen into jacket it is straight lines not Coil - ?? right ??

But this is only one data point and I will need lots of data points to deduce a formula for how hot this wire gets in various lengths, with 13 volts not 12, 30 and 32 gauge, etc.

Doesn't anybody have a formula for the Simplest Condition (no air circulation, etc)

 

[Redbelly98]

So when I have my 16 feet of 32 gauge test wire attached to the battery charger - how in the world can I measure what amps are really being drawn ?? If I put my ammeter on the circuit (it will then be in parallel with my test wire) ?? it will just draw lots of amps instead of reading what amps are being drawn by the wire ?? if that is the case what good is an ammeter ??

Put the ammeter in SERIES with the test wire to measure the current through the wire.

 

[Phrak]

You're intent is to get heat to your skin. At a temperature of 107F this is going to take a very, very long time. But the smallest air movement will carry this away. Without leathers, buffeting from the air will pump most of it out through the smallest seams. You need a lot more power.

 

[uart]

You're intent is to get heat to your skin. At a temperature of 107F this is going to take a very, very long time. But the smallest air movement will carry this away. Without leathers, buffeting from the air will pump most of it out through the smallest seams. You need a lot more power.

I don't agree with that, 75Watts is similar to the basal metabolic rate of a human and seems like a good starting point to me. Sure you still want good insulation between the heating coil and the outside of the jacket to stop the heat being drawn away to rapidly.

DrAlloway, I don't know if this is too hard to do (physically) but one thing that would be a huge help in distributing the heat (to prevent hot spots that could potentially burn you or the jacket) would be if you could wrap the wire flat in Al foil (to make it like a foil ribbon instead of a plain wire). I guess that doing this might make it too hard to insert into the jacket, but it would definitely aid in distributing the heat and keeping the temperature more uniform.

 

[Phrak]

I don't agree with that, 75Watts is similar to the basal metabolic rate of a human and seems like a good starting point to me. Sure you still want good insulation between the heating coil and the outside of the jacket to stop the heat being drawn away to rapidly.

So I checked around and found that heated jackets run anywhere from 65 to 100 Watts. I think the answer is somewhere in between 75 Watts and 'alot more'. These jackets are designed to retain heat, and reduce excess air circulation. It would depend a great deal on what kind of jacket is being modified.

 

[Homer Simpson]

If I only need 1/2 power for heating on a particular day - a potentiometer will still draw 150 watts instead of 75 watts

Is this true? I thought they stepped down the voltage via multi tap transformer sort of idea, so lower voltage in the circuit, lesser wattage draw.

If they function as a resistor than what you say is true.

To be honest, I am not sure.

 

[Homer Simpson]

If I only need 1/2 power for heating on a particular day - a potentiometer will still draw 150 watts instead of 75 watts

And, after googling it for a second, I see you are totally right, as I am sure you know already.

 

[quadraphonics]

Doesn't anybody have a formula for the Simplest Condition (no air circulation, etc)

Well, you really need to specify some kind of thermal model here. In the very simplest case, where the wire is assumed to be totally thermally insulated, the temperature will linearly climb without bound (i.e., you'll either catch on fire or part of the circuit will fail). Obviously, that's not very realistic. It really comes down to figuring out how much heat is going to be lost to the environment; you want the heater to output something close to that (much lower, and you will still get cold; much higher, and you will eventually overheat). This, in turn, depends on how the wire is coupled into the jacket, how insulative the jacket is, how cold the ambient air is, how humid the ambient air is, and how fast the air is moving over the outside of the jacket. I don't have an intiutive idea of what the total heat loss you're looking at is, but you will need to posit at least a preliminary idea in order to proceed with the design.

Said another way, in this application, YOU are the heatsink :]

Building in some facility to control the amount of heating is also a good idea: this will extend the range of climates you can use the jacket in, and keep you maximally comfortable in all of them. However, you will still need to build in some reasonable upper and lower limits on the design, in order to prevent fire/overheating on the one end, and to eliminate useless operating points on the other extreme. Once you have some reasonable, safe operating limits in place, you can use the variability to experiment in the field (record the temp/windspeed/humidity, and then drive around adjusting the temp until it's just right. Then go back to the lab and see how much current you were drawing at that setting).

Also be sure to check that the melting points of any materials in the jacket close to the heating wires is not prohibitive.

 

[DrAlloway]

You're intent is to get heat to your skin. At a temperature of 107F this is going to take a very, very long time. But the smallest air movement will carry this away. Without leathers, buffeting from the air will pump most of it out through the smallest seams. You need a lot more power.

With Heated Clothing on a motorcycle one usually wears:
base layer - for dead air space and moisture wicking
lightweight long johns
heating layer
protective layer (usually leather with insulated liner and with armor).

Commercial suits (costing about $700) include
80 to 100 watts for jacket
28 watts for gloves
44 watts for pants
28 watts for socks

Most guys riding around have their heated layer on half power when the air temp is between 32 and 40F.

So I am confident on the watts needed to keep me warm.
However, commercial suits have a Heat Controller (high power triac or 555 timer) which they sell for $100 - and I am too cheap to buy --

So I am using multiple parallel loops of heating wire to enable me to vary the temperature. I just need to make sure that no one loop is going to be too hot and burn me, especially in gloves and socks because it is very hard to sew lots of feet of wire there.

 

[DrAlloway]

where the wire is assumed to be totally thermally insulated, the temperature will linearly climb without bound (i.e., you'll either catch on fire or part of the circuit will fail).

This may have been obvious to everybody else, but me - but now that you say it, it makes sense. The wire will continue to get hotter and hotter as more energy (watts) is pumped into a closed system. So the question is how open is the system. And my design goal is to establish equilibrium at a target temperature.

So if commercial products are 80 to 100 watts for the jacket. Most guys use half power. Most guys have outer layer leather jackets with about the same thermal properties as mine. And fine tuing of heat loss is easy with zippers everywhere.

Therefore I should design my jacket with multiple parallel loops providing optional heating levels of 20 watts, 40 watts, 60 watts, 80 watts, and 100 watts - and while I am riding I can make adjustments with my On/Off switch and zippers.

So... there is no answer to my original question of how hot will the wire get, but that is OK because it was the wrong question. The question should have been - how many watts do I need in my gloves to compensate for heat loss at 35F and 70 mph. And I already know the answer - 28 watts is what all the commercial guys sell.

Thanks, everybody, I have learned lots and will be back soon with another dumb *** question I am sure, Bob

 

[david90]

I am making a heated motorcycle jacket - so 13 volts DC (actual measurement while riding).

For heating wire I am using 30 gauge (7 strand x 40 AWG) tinned copper wire with Teflon insulation (good to 250C) which has a resistance of 0.102 ohms per foot (actual measurement as versus 0.103 from tables).

I will sew 22 feet of this wire into my jacket so that gives me:
2.24 ohms, 5.8 amps, and 75 watts.

75 watts over 22 feet is 3.43 watts per foot.

The practical question is will this wire burn me or melt my polyester jacket ??

I do Not need the exact temperature of this wire. There are no second or third degree issues as the wire is sewn into polyester insulation between my jacket shell and liner. So there is NO air circulation, fan, or any complications.

There must be a formula for calculating the APPROXIMATE temperature of this wire.

Any help will be greatly appreciated as I am definitely not an electrical engineer.

thanks, Bob

I think it is best if you design a controller to actively regular the temperature so that the temperature will always be at your target regardless of your speed. U don't want to keep on adjusting your pot as you speed up or slow down.

I wanted to do something similar and thought about sewing the heating element to clothings that are tight fitting like thermals. This way it will be a lot more efficient than sewing it into your loose jacket where the moving air can carry the heat away.

 

[Redbelly98]

I think it is best if you design a controller to actively regular the temperature...

In principle, yes. But here I think the best thing is to get something simple working first. This may be the OP's first electronics project.

Bob, if you get it working feel free to post back here and let us know. It can be a challenge to get a project like this to work, but it's great when it does.

Regards,

Mark

 

[DrAlloway]

I think it is best if you design a controller to actively regular the temperature so that the temperature will always be at your target regardless of your speed. U don't want to keep on adjusting your pot as you speed up or slow down.

I wanted to do something similar and thought about sewing the heating element to clothings that are tight fitting like thermals. This way it will be a lot more efficient than sewing it into your loose jacket where the moving air can carry the heat away.

Can't use a pot on a bike because a pot uses full amps and bike's can't waste them -- see previous.

Bike's have regulators (after generator) so that speed does not effect voltage. In fact, the engineers who designed the regulator on my bike have it putting out 14 volts at idle and 13.1 at 2,000 rpm.

You are right about keeping the heating clothing close to your body. All commercial makers design their cloths to fit tight just to keep the heat near the body. I usually wear an Xtra-Large jacket, so I am sewing the heating wire into a Large jacket the fits snug. Still enough room under for a base layer - have to wick moisture away - AND IF some of my wires get a little hot, I want something to protect my skin and spread the heat around.

 

[DrAlloway]

In principle, yes. But here I think the best thing is to get something simple working first. This may be the OP's first electronics project.

Bob, if you get it working feel free to post back here and let us know. It can be a challenge to get a project like this to work, but it's great when it does.

Regards,

Mark

I will let you guys know how it works out. I am going to finish the jacket and ride with it and see how things go before doing the gloves, pants, and socks. There is a good chance of lessons learned from the jacket that can be applied to the pants, etc.

I have made my own aux brake lights with LEDs but basically this OP is NOT an electrical engineer. In fact, I wanted to make my own heat controller. Can't use a pot (wastes amps). Some folks suggested using a 555 timer to turn On/Off at varying rates but I don't have the skills. I did find (at Home Depot) a dual digital light dimmer that varies the rate and duration of light On/Off to achieve dimming - however it is 120vAC and converting it to 12vDC is something I don't know how to do.

 

[Proton Soup]

this circuit might work as a controller. http://www.allaboutcircuits.com/vol_6/chpt_6/9.html

 

[quadraphonics]

This may have been obvious to everybody else, but me - but now that you say it, it makes sense. The wire will continue to get hotter and hotter as more energy (watts) is pumped into a closed system. So the question is how open is the system. And my design goal is to establish equilibrium at a target temperature.

Yes, exactly.

Therefore I should design my jacket with multiple parallel loops providing optional heating levels of 20 watts, 40 watts, 60 watts, 80 watts, and 100 watts - and while I am riding I can make adjustments with my On/Off switch and zippers.

So the idea is that you can hook up as many loops as you want when you plug in the jacket, depending on how cold it is, and then fine tune from there with zippers (or just by switching off)? That seems like a good way to start. I would avoid using a potentiometer here, for the reasons people listed above, although you might consider hooking one up for test purposes once you have a working baseline system.

So... there is no answer to my original question of how hot will the wire get, but that is OK because it was the wrong question. The question should have been - how many watts do I need in my gloves to compensate for heat loss at 35F and 70 mph. And I already know the answer - 28 watts is what all the commercial guys sell.

That sounds look a good baseline to start with. But even once the total power dissipation is in the correct range, you still need to ensure that the wire and insulation won't overheat. This is a question of what the total volume and circuit area of the heating wires are, and what materials they're encased in. Again, using something along the lines of existing commercial products should be a good place to start, but be sure to test it out thoroughly before trying it on yourself :]

Once you have a satisfactory baseline system working, you should consider active control and then closed-loop control. In the latter case, you would build in some temperature sensors and use data from them to automatically adjust the heating power for optimal comfort. I.e., the motorcycle equivalent of climate control :] You could also build in safety systems to prevent overheating in such an approach. Of course, doing all that will be a more involved, expensive project, but still... sounds like fun.

 

[DrAlloway]

At this point my active temperture control is going to be a biological feedback system -

if I get too hot I will have a switch strapped to my left thight and I will simply turn it off.

Once I get everything done and the system stablized I would like to have a better heat controller.

I am still tempted to try and convert a digital light dimmer (like Lutron at Home Depot - see link). It is designed for 120vAC and its probably not waterproof - but if I could make it work for 12vDC it would be great - anybody know how to make the change ?

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100129934&N=10000003+90401+503054

 

[david90]

At this point my active temperture control is going to be a biological feedback system -

if I get too hot I will have a switch strapped to my left thight and I will simply turn it off.

Once I get everything done and the system stablized I would like to have a better heat controller.

I am still tempted to try and convert a digital light dimmer (like Lutron at Home Depot - see link). It is designed for 120vAC and its probably not waterproof - but if I could make it work for 12vDC it would be great - anybody know how to make the change ?

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100129934&N=10000003+90401+503054

Good luck and don't turn into ghost rider if you know what I mean.

 

[DrAlloway]

Actually, when I first started designing this project, that was my daughter's first reaction:

"This sounds like a ball of fire roaring down the road."

I have now finished sewing all four loops of wire into my jacket.

I have a bunch of plugs to solder over the weekend - connecting 32 gauge Teflon insulated wire to plugs is not easy - if you pull on the plug to make a connection you can break the 32 gauge wire - and wearing gloves only makes it more likely.

?? still no suggestions on how to convert a 120vAC digital light dimmer to 12vDC ??

 

[dlgoff]

Here's a 12 volt dimmer that is suspose to be rated at 7.5 amp.
Without the plate and a smaller knob, it might work for you.
http://www.dyersonline.com/Products/12-Volt-Light-Dimmer-Switch__18-0600.aspx"

 

[Redbelly98]

Here's a 12 volt dimmer that is suspose to be rated at 7.5 amp.
Without the plate and a smaller knob, it might work for you.
http://www.dyersonline.com/Products/12-Volt-Light-Dimmer-Switch__18-0600.aspx"

DC or AC?

 

[david90]

Actually, when I first started designing this project, that was my daughter's first reaction:

"This sounds like a ball of fire roaring down the road."

I have now finished sewing all four loops of wire into my jacket.

I have a bunch of plugs to solder over the weekend - connecting 32 gauge Teflon insulated wire to plugs is not easy - if you pull on the plug to make a connection you can break the 32 gauge wire - and wearing gloves only makes it more likely.

?? still no suggestions on how to convert a 120vAC digital light dimmer to 12vDC ??

I can't help you with the 120VAC dimmer because I have no idea how it is designed.

This circuit looks good for your project though.

The power rating is depends on the FET transistor so you can replace it with the one that suits your need.

 

[Homer Simpson]

How about this as a possibility: use an on/off control or thermostat of some sort. I've been trying to think of what could be used for cheap.

The best I can think of for on/off would be the safety cutoff bimetallic strip trip for a Hair Dryer. They are apparently designed to cut off power at around 60 degrees C, so as to not burn skin. You could insulate this directly around the heating wire, or wrap a few heat wire loops around the sensor deliver more heat to it, and leave it uninsulated to allow strip to cool after after acting. This also acts as a good safety feature incase you are in a situation where heat loss from the coat drops for a while (ie. in traffic) and the wire would start heating up beyond what it was while moving on the bike.

http://home.howstuffworks.com/hair-dryer4.htm

The other thing that may or may not work would be to grab a thermostat from a toaster oven, clothes dryer...


http://sunnergroup.manufacturer.glo...9/pdtl/Toaster-oven/1008140892/Thermostat.htm

http://sanchang.manufacturer.global...599/pdtl/Thermostat/1008870226/Thermostat.htm (has plus minus 2 degrees C control)

http://www.appliance411.com/parts/showcase.dryer-thermo.shtml

You could maybe sew one of these devices in close prox. to the heating wires, then set it and foget it.

 

[dlgoff]

DC or AC?

Humm. I assumed it was DC since the site was advertising "RV Lighting Accessories" but they really don't say. Maybe it is AC in which case it wouldn't work. Here's their "Indoor Lighting" page.
http://www.dyersonline.com/Departments/RV-Lighting-Accessories/Indoor-Lighting.aspx"