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Heat. Answered

So I want to make a necklace with a pendant that will always be warm. I dont know how to go about this so if anyone can help thatd be great. I was thinking possibly chemicals but i dont know if thats safe nor do i know anything about chemicals. Id prefer something that once i finish it ill never have to change or switch anything out but whatever works.

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westfw

9 years ago

Not possible. Conservation of energy... I think there are some materials that consistently FEEL warm (or more often cool) due to the way they absorb and/or reflect/transmit body heat...

They could use Plutonium-238, curium-244 or strontium-90, these all emit heat for a very long time, however they also emit a lethal dosage or radiation in minutes..... (( not to mention most people can't get there hands on even very small amounts of them, they are only for special applications like heating deep space satellites, and for power generation of those same satellites ))

How about a mini fusion plant! lol!

You could use a simple catalytic heater, there are small ones, about the size of a Zippo, infact I think Zippo even makes some and they run several hours on a very small amount of fuel... Try googleing pocket hand warmers, the one I seen at a local camping store was only $20 and looked nice.... Or you could use Sodium Acetate, but you would have to dip the pendant in boiling water after each use, but it would give you about 30 mins of heat......

and going with a fuel powered device will always be smaller then a battery operated device, 1 liter of #1 fuel oil will output about same amount of heat an 11,000 watt heater will output in one hour (( some where in the area of 38,000 Btu )) and in my experience that 1 liter in fuel is the same as carrying 20 car batteries...

Your best bet for electrical heating is a low-value resistor. They won't waste any power emitting something like light; it'll all end up as heat, right away. And with nicely predictable power consumption, too. I'd guess that somewhere around 1/4 W would make a small object noticeably warm (consider that a 4W nightlight bulb, or a 1W power LED, gets quite HOT.) A small 100mAH Lithium battery has about 0.4 WH, so it might maintain 1/4W of heating for a couple hours...

The whole point of LEDs, besides being energy efficient, is that they hardly produce any heat. You're probably thinking of an incandescent light bulb, which produce lots of heat. Unfortunately, they use a ridiculous amount of electricity, too.

Ah, yes, my mistake, a very small bulb is what I mean.

That would work, but again, it would be very inefficient. You would have to replace the battery every couple of hours. Maybe if you built a charger that works like a self-winding watch...

Well is there a material i could use that would use body heat to warm it? maybe holding it in your hands would heat it or it could use friction from rubbing your hands? just so its warm while youre holding it.

. An exothermic chemical reaction will only last a few hours (probably minutes, with the small volume you are dealing with).
. Batteries run down quickly when used for generating heat. And the limited volume you have to work with means you can't carry much battery.
. I'd explore using a material that doesn't conduct heat very well, as per westfw. It will never really feel warm, but, being worn close to the body, should be close to "neutral."
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. BTW, skin temperature is about 92oF/33oC, so your pendant needs to be hotter than that to feel warm.