Posted: 5/21/2009 4:54:05 AM EDT
| Who knows anything about these? I want to obtain a few samples, say 1/2 square, for an OTC medical application. |
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Quoted:
Who knows anything about these? I want to obtain a few samples, say 1/2 square, for an OTC medical application. While they can produce very localized cooling, you need to dissipate all the heat removed fromthe cold side, plus the large amount of heat generated by driving the device. The efficiency is not very good. Think like 20% or so. |
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Neat factoid: reverse the current and the heat flow reverses. I believe they work as well in either direction. Be careful soldering them. It is very easy to destroy the junction with too much heat. Tin-lead solder's melting temperature is too high, try to find low temperature bismuth-based solder. Forget any of the new lead-free stuff. A good deal of the inefficiency is caused by air circulation between the hot and cold side. We used them in a vacuum application and the efficiency improved dramatically when air was removed. If you can arrange for them to be in a sealed housing, it might help to flush them with argon. Some reading here: Melcor |
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If you just need heat, why do you need a peltier at all? Good point. Here's my application: I've learned that mosquito bites can be treated with the direct application of heat. Heat (high enough to hurt) 'dries up' the histamine at the site, causing the bites to stop itching. I want to create a handheld portable 'pen' capable of generating enough heat to treat bites in this manner. The Peltier junction was first to come to mind. I haven't even started looking at other options. |
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Quoted:
Quoted:
If you just need heat, why do you need a peltier at all? Good point. Here's my application: I've learned that mosquito bites can be treated with the direct application of heat. Heat (high enough to hurt) 'dries up' the histamine at the site, causing the bites to stop itching. I want to create a handheld portable 'pen' capable of generating enough heat to treat bites in this manner. The Peltier junction was first to come to mind. I haven't even started looking at other options. Shape nichrome appropriately, add battery and variable resistor to control temperature. |
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Peltier modules require a reasonably regulated voltage source along with a means to either dissapate the heat or the cold. If all you want is a heat source, just use a resistor, easy to calculate the heat energy, wattage and best of all cheap. Use a SMT resistor potted in an aluminum button.
FWIW, someone invented something like this a while back, it was and electronic itch stopper and/or a pimple killer pen, though I think it used a low level electric shock like a TENS or Stim unit to do the same thing. |
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a peltier for a battery powered application would be too inefficient. you should simply use a heating element. use material with the lowest heat capacity you can find, so it heats up quickly, cools off quickly when done, and doesn't waste heat on anything but heating the mosquito bite. that would save batteries.
how about integrating a temp sensor and a microchip so you apply it to the bite, press a button, it turns on and only heats up to a certain temp and shuts off. sort of like giving yourself a shot. |
| Resistance heating sounds like the simplest approach. You might look into positive temperature coefficient (PTC) heating elements - Their resistance changes dramatically with temperature, making them essentially self-regulating. Several companies (Tyco/Raychem "PolySwitch", Bourns "MultiFuse") make PTC resettable fuses that behave the same way - Even through they're designed for circuit protection, they make pretty decent self-regulating heating elements. They're small, cheap, and available in a wide variety of current ratings. Mouser Electronics stocks both brands. |