I looked around at other questions, and either I didn't understand what all I was reading, or it didn't answer my question so if there is an article that I've missed feel free to redirect me.
I'm fairly new to electronics, and came in through Arduino so I'm pretty fuzzy when it comes to the actual electronics behind how things work.
I'm trying to create a heating device for heating a chest freezer that I'm trying to convert to a incubator. I have the "coding" side done with Arduino, now I'm trying to build the electronics. I have some relays that I'll be using to turn things on.
HERE IS MY QUESTION
I have a 12v 6a DC power supply that is powering my entire project. I'm trying to use 4 x 10W 12ΩJ Cement resistors. How should they be configured to produce my needed heat.
So I thought to myself, "I have 12v * 6a = 72w power supply, if I'm using 4 x 10w resistors 72 watts would be too much for them." I hooked them up this way though, the resistors in series, and they barely heat up, so I must not know how these things work even though I thought I did.
Is there a good way to calculate how much power a resistor should get for me to reach a specific temperature. Is there a calculator, or anything that can be used, or a formula, or is it resistor specific?
If I connect Just 1 or 2 in series they get ALLOT hotter, but then I'm worried about burning out the resistors.
Any help would be great, even if its a bunch of "Go look and read over here." comments.
ADDITIONAL DETAILS as Requested
The space being heated is about 1.5 Cubic meters, I don't know the insulation type, its a freezer, and the other unit I'm looking to make this for is a wine cooler.
The reason for using 12v DC is incase of prolonged power outage that it can be easily run off of a battery back up, or a solar panel / battery system.
The space can be heated with a 40w light bulb fairly well. There are other commercial devices like this, that use a similar setup.
The temperature I'm hoping to achieve varies depending on the egg, but no more then 100F.
As far as the 72 WATTS I was just saying that is what my DC supply is putting out, It would be much more convenient to run it on less obviously.