Heated Clothing Potentiometer Help

[_Nate_]

Hello, so I have recently got 30 awg teflon wire in the mail, and I want to use it for heated clothing. I was trying to use a 10k pot in order to be able to control the heat, but when the resistance is lowered all the way, the potentiometer starts glowing. I am using a 7.4v power source, and without any resistance, the wire gets heated to a good temperature, but then the battery case starts smoking. I need some help figuring out what to use to get a variable temperature that can get hot enough but not have a smoking battery tray.

 

[Bluejets]

Pot won't work. Maybe has a rating of 1/8 to 1/4w at best.
Teflon wire would need to be resistance wire.
Battery too small at a guess. Won't last long at best.
Smoking battery tray means you are headed for a disastrous ending.

Things like this are designed from the bottom up, not the top down.
First find energy requirements.
Distribute over given area.
Then capacity or wattage of heater over that area.
Then input requirements.
Then control requirements.(usually pwm for dc supply)

 

[kellys_eye]

Best look up heating tape for clothes rather than trying to design your own heating element - far safer. Then, as mentioned by @Bluejets do the maths and use the proper control circuitry.

Any Googled site on power control will reveal the basics.

 

[_Nate_]

Thanks!

 

[dave9]

You're totally ignoring the current in every part of the circuit. Your battery case may simply be too low end junk, or at least the wrong materials, to support what you're trying to do. Your battery may be undersized too, what good is staying warm for only a little while when people usually need warmth only after being outside for closer to an hour or more?

This project is beyond your skill level due to the fact that you intend to wear this on your person in use. Further if your 7.4V power source is 2 x Li-Ion batteries, you better put a protection circuit between them and the rest, due to the resistive heating element which would drain them down to nothing and cause damage.

I have seen people stumble through trying to build battery powered clothing heaters before and it isn't pretty, they usually give up and wasted time and money. I would advise buying a ready made heated (jacket or gloves, whatever) and appreciating that whoever designed that, spent years learning the things they needed to do, in addition to MUCH testing to arrive at the product result.

 

[_Nate_]

You're totally ignoring the current in every part of the circuit. Your battery case may simply be too low end junk, or at least the wrong materials, to support what you're trying to do. Your battery may be undersized too, what good is staying warm for only a little while when people usually need warmth only after being outside for closer to an hour or more?

This project is beyond your skill level due to the fact that you intend to wear this on your person in use. Further if your 7.4V power source is 2 x Li-Ion batteries, you better put a protection circuit between them and the rest, due to the resistive heating element which would drain them down to nothing and cause damage.

I have seen people stumble through trying to build battery powered clothing heaters before and it isn't pretty, they usually give up and wasted time and money. I would advise buying a ready made heated (jacket or gloves, whatever) and appreciating that whoever designed that, spent years learning the things they needed to do, in addition to MUCH testing to arrive at the product result.

Thank you very much for your wisdom.
But why do I see videos for heated insoles in a simple circuit?

 

[dave9]

^ Because the circuit only SEEMS simple after they have spent the time to figure out how to do it. If you want to just duplicate what some video did and it seems like a sound design, that is different from rolling something else from scratch.

A few things that are wrong with the original items include:

1) A piece of wire is a terrible heating element for clothing. You want something that spreads out heat, not melts your coat or burns your skin. A tiny wire can get too hot and still the total wattage effective to provide warmth is low. Reduce the heat density.

2) A potentiometer is not capable of handling the current. You would have it basing a transistor or providing feedback to a voltage or current regulating controller.

3) You didn't mention the specifics of the power source. In general enough heat to bother with, tends to be a big bulky battery worthy of mention. An exception might be gloves, if the wearer has to have thin gloves for dexterity reasons then a little bit of heat goes a long way. Insoles? Meh, wear thicker socks and insulated boots.

4) I dismiss the idea that it really needs to have temperature control. It would be simpler to just set it up where it is within the current limits of everything to run at full power then you merely switch it off when you don't need it. Besides, cold body parts tend to get numb and you might not even realize you're burning yourself or your clothing so the max power without reduction could be lower than that which destroys components. Kellys_Eye already mentioned heating tape. That would be better than a wire and there are different resistances vs lengths to choose from.

However I still feel it is not worth the bother. There are ready made solutions. It would be different if you were saving a lot of money and not spending much time because you already had the parts and knew how to do it.

On the other hand I am not trying to discourage experimentation and learning along the way. I would consider this more of a learning project than a way to stay warm before winter is over.

 

[_Nate_]

^ Because the circuit only SEEMS simple after they have spent the time to figure out how to do it. If you want to just duplicate what some video did and it seems like a sound design, that is different from rolling something else from scratch.

A few things that are wrong with the original items include:

1) A piece of wire is a terrible heating element for clothing. You want something that spreads out heat, not melts your coat or burns your skin. A tiny wire can get too hot and still the total wattage effective to provide warmth is low. Reduce the heat density.

2) A potentiometer is not capable of handling the current. You would have it basing a transistor or providing feedback to a voltage or current regulating controller.

3) You didn't mention the specifics of the power source. In general enough heat to bother with, tends to be a big bulky battery worthy of mention. An exception might be gloves, if the wearer has to have thin gloves for dexterity reasons then a little bit of heat goes a long way. Insoles? Meh, wear thicker socks and insulated boots.

4) I dismiss the idea that it really needs to have temperature control. It would be simpler to just set it up where it is within the current limits of everything to run at full power then you merely switch it off when you don't need it. Besides, cold body parts tend to get numb and you might not even realize you're burning yourself or your clothing so the max power without reduction could be lower than that which destroys components. Kellys_Eye already mentioned heating tape. That would be better than a wire and there are different resistances vs lengths to choose from.

However I still feel it is not worth the bother. There are ready made solutions. It would be different if you were saving a lot of money and not spending much time because you already had the parts and knew how to do it.

On the other hand I am not trying to discourage experimentation and learning along the way. I would consider this more of a learning project than a way to stay warm before winter is over.

I agree with setting a fixed temperature. My plan was to have one central hub of power, totaling possibly 14.8v 700mah, with voltage regulators for the heated clothing portion. I also want to have the heat centralized on and around the chest area, not shoes or gloves.

Power specifications: I have a total of 4 3.7v 700mah batteries I use in series in a AA battery holder. I have 2x, 3x, and 4x AA battery holders but for the 7.4v I mentioned earlier was using the 2x holder.

 

[dave9]

There's the thing. 7.4V x 0.7Ah = 5.18Wh. You'd start out around 5W for an hour but without regulation (a loss in itself) drop in power output from there. 5W really isn't much for core heating. The average female at rest produces close to 100W. Moving about or a male especially, inches up towards 200W. 5W is not much more heating, a trivial amount except for extremities like fingertips.

Also as I mentioned previously and seems to be the case, you have Li-Ion cells so you need a low discharge cutoff circuit or they'll be damaged the first time you run it too long.

IMO a more practical amount of heat and runtime would require at least 4 x 18650 cells and go up from there.

 

[_Nate_]

There's the thing. 7.4V x 0.7Ah = 5.18Wh. You'd start out around 5W for an hour but without regulation (a loss in itself) drop in power output from there. 5W really isn't much for core heating. The average female at rest produces close to 100W. Moving about or a male especially, inches up towards 200W. 5W is not much more heating, a trivial amount except for extremities like fingertips.

Also as I mentioned previously and seems to be the case, you have Li-Ion cells so you need a low discharge cutoff circuit or they'll be damaged the first time you run it too long.

IMO a more practical amount of heat and runtime would require at least 4 x 18650 cells and go up from there.

I do own 4 of the batteries to provide 14.8v at 700mah

 

[_Nate_]

So, I found this on eBay, would this work in series with some sort of 6v power regulator board?
https://www.ebay.com/itm/12V-Accumu...098548&hash=item544cd8d84e:g:HcwAAOSw74NZjCrR

 

[_Nate_]

There's the thing. 7.4V x 0.7Ah = 5.18Wh. You'd start out around 5W for an hour but without regulation (a loss in itself) drop in power output from there. 5W really isn't much for core heating. The average female at rest produces close to 100W. Moving about or a male especially, inches up towards 200W. 5W is not much more heating, a trivial amount except for extremities like fingertips.

Also as I mentioned previously and seems to be the case, you have Li-Ion cells so you need a low discharge cutoff circuit or they'll be damaged the first time you run it too long.

IMO a more practical amount of heat and runtime would require at least 4 x 18650 cells and go up from there.

Will that work? Or would it be better to make my own?

 

[BobK]

No, that is entirely the wrong thing. What kind of batteries do you have? Many have the protection circuit built in.

Bob

 

[_Nate_]

No, that is entirely the wrong thing. What kind of batteries do you have? Many have the protection circuit built in.

Bob

I have efest 3.7v 700mah IMR batteries

 

[Bluejets]

Think of it this way perhaps....you are trying to use a AA battery to start a truck.

 

[AnalogKid]

Regular wire, no matter what the insulation is, will not work in your application; its resistance os over 1000 times too small. You need a special, high-resistance wire, probably a variation of nichrome, that is designed specifically for your voltage and current levels and insulated. As far as I know, this is not a catalog item.

ak

 

[Hopup]

There are lot of different flexible heat pad available in Ebay for example. Silicon heat pads 5 to 100+watts and also fabric pads.

 

[_Nate_]

Thank you all so much for sharing your wisdom with me! I really appreciate all the help from all of you. I will rethink my methods and not use the teflon. Thanks again!