Help with Thermostat Control for 12V Fridge

Not sure what wrt means, and thermal inertia factor is way over my head for this project....
I have enjoyed researching every suggestion.
Thanks, Mac

Yes, I've used the ds18b20 before, but never had one available. The metal cased unit would have worked great here, especially with its 0.5% accuracy. Can you give me the 2x10k link again. Thanks

My NTC thermistor is a Vishay NTCLE100E3 small teardrop unit.
Here is data sheet from my local supplier:
ntcle100.pdf (

Should the metal plate be on standoffs away from the molded plastic housing?

Its not clear to my what the aluminum plate brings to the accuracy of the sensor. I would think it only matters IF there was air flow in the container that would pickup changes more quickly.

It should not be touching anything that can suck or add heat from the plate.

Thermal capacity (aka thermal inertia) is the amount of heat required to heat a particular material.
The best example is:

You put a piece of meat in the microwave. The meat has some fat around the edge. You turn the microwave on and the fat gets hot quickly, the meat takes longer. Periodically you hear a "POP" that is from the fat getting so hot it vaporizes.

So here the fat takes little energy to heat up while the meat takes more energy. The fat has a lower thermal capacity than the meat, so it takes less energy to heat up.

BTW WRT := with respect to

There is air flow inside the box, as there is a fan circulating the air around the inside aluminum fins of the Peltier module. Without the metal plate the NTC's had a very slow temp response, or none at all.

Yes, I understand thermal inertia in context, but there would be complex design computations involved to link a NTC with the heat capacity of different size metal plates, which is way beyond my radio tech qualifications. I mounted the heat plate on standoffs, to take advantage of the air flow and increase response time. See attached photo.

Thanks for confirming the 25-32k range of the series resistor for my temp range. Changing from 10k will increase the resolution, so helps to fine tune the circuit. Mac

Thanks to everyone for all their technical comments and advice. We no longer have to buy ice for our camping cooler, and it is no longer freezing the Lettice. :sunglasses: