I am wanting to build a heated temperature controlled pouch. I’m needing a heated pouch that is able to reach and maintain temperatures of 98°F-102°F for 6 to 8hrs with a 5v-12v power supply.
You need to know
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The temperature on the outside of the pouch as well as on the inside
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The heat transfer coefficient of the material (how well it insulates)
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Newton’s cooling law: https://physics.stackexchange.com/quest … ferent-tem
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Apply Newton’s law to figure out how much energy it will take
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From the above, you will know the electrical energy needed
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Now you know the power requirements, you need a temperature controller. You can buy those cheaply off the shelf: http://www.ebay.com/bhp/temperature-switch