Looking for advice building a handheld heating element that uses nichrome wire. The nichrome wire will wrap around an aluminum bottle which can heat 3oz of coconut oil inside to 100 degrees F.

I've been trying to find some circuit designs by looking at vaporizers, electric water boilers and curling irons, but I am totally new to electronics and totally at lost on where to start :/ I would love any advice to point me in the right direction. Right now I'm looking at 123D circuits and Arduino for micro controllers.

This device needs:

• Heating element that can warm contents 3oz of coconut oil to
• On/off switch
• Ni-chrome resistor
• Bimetallic thermal switch to shut off heating at a certain temperature
• Power source-battery

 

Here's the thermodynamic part. Your average low temperature is 57 degrees in January. You will need 2.36 watt hours to heat the oil. A square 9 volt battery contains 4 watt hours. If you use a small container, you could do this by exhausting one 9V battery. An alkaline D Cell would work, too.

That leaves the heating element, the thermostat, and the switch.

 

This thread kinda makes me wish I lived in San Francisco.

 

I know you said you want to use electricity as your heat source, but for 100°F you should consider chemical energy. There are already self-heating soup cans and such, and you might be able to re-task those hot pads they sell for aches and pains, or the kind used for keeping your hands warm. A solution using these would be far simpler than a 100°F micro-oven. The hot pads, at least, are rechargeable (you cook them in a microwave).

@#12, did you account for the lower heat capacity of coconut oil? I suppose it's density and Cp are quite a lot less than water.

 

did you account for the lower heat capacity

No. I just called it water. There are plenty of other uncertainties, like the size of the aluminum container that the oil will be in and also needs to be heated, whether the oil really came out of a refrigerator at 47 degrees F, whether the TS will ever come back, etc, etc.

 

How are you going to wrap the Nichrome wire around the aluminum bottle without bypassing the current into the bottle and basically making a short circuit?

 

I know you said you want to use electricity as your heat source, but for 100°F you should consider chemical energy. There are already self-heating soup cans and such, and you might be able to re-task those hot pads they sell for aches and pains, or the kind used for keeping your hands warm. A solution using these would be far simpler than a 100°F micro-oven. The hot pads, at least, are rechargeable (you cook them in a microwave).

@#12, did you account for the lower heat capacity of coconut oil? I suppose it's density and Cp are quite a lot less than water.

I use foot warmers from Wal-Mart during winter and if left to open air they get quite hot. One side has a temporary adhesive to stick to your socks. Stick one on each side of an aluminum container in open air and in 10 to 15 minutes it should be ready.

 

Do you have to use a battery? You'll be burning through batteries and generate a lot of waste. Just use the footwarmer (I assume they're 110V?) and a 110V plug with a thermostatic probe like this:

http://www.amazon.com/30-110-Celsius-Thermostat-Temperature-Controller/dp/B00E1LAX6K

It has a probe to put in the oil and a dial to set the temperature. (See photo below -- I hope it comes out in the post)

Get someone who knows how to wire 110V circuits safely, use 0.250" spade-lug crimp connectors on the above thermostat and put it in a plastic box so no wires or terminals are exposed. It'll be a simple series circuit coming from the wall through the thermostat through the footwarmer and back to the wall plug.

Spade Lug crimp connector for the thermostat look like this -- fully insulated. Don't get the ones that are just metal. Amazon doesn't have a decent selection, but you can get them at any hardware store. Get the blue ones -- they should fit an 18 gauge electrical cord. If you want to use thicker wire and be safer, use 16 gauge electrical cord and the yellow spade lugs.

http://www.digikey.com/product-detail/en/3-520406-2/A27856CT-ND/385317

Thermostat looks like this: