# Circuit analysis of hobby project: insulated wine cabinet with cooler

#### caje

Joined May 2, 2020
9
I am sketching a hobby project, and I would like to sort out the electronics on paper first. I am building an insulated wine cabinet and have calculated that I can expect a heat-influx of around 15-20W under normal operating conditions. Hence, I need some cooling capabilities. I am looking at thermo-electric cooling devices for low-noise cooling. I am very rusty in my electrical engineering, and have no experience with TECs, so it would be great if someone can confirm some of my statements and calculations.

Specifically, I am looking at the following components:

* Peltier thermo-eletric cooling module (12V/4.3A, Imax=14.6V) - this is the smallest available
* Velleman 137 Thermostat with relay (12V/0.1A)

The thermostat module can be configured to a certain temperature (15°C) and contains a relay that activates with a 1K hysteresis. This seems good for my use-case.

Looking at the Peltier coefficient of performance graph I should be able to reach a COP of ~2.6 for I/Imax=0.2 at dT=10°C, which I interpret as having to divide voltage from 12V to 0.2*14.6=2.92V, and if I supply this with 3A I am consuming 2.93V*3A=8.76W and hence moving 2.6*8.76W=22.77W of heat. I may want to supply a little more voltage for being sure on hot days, but let's assume this for an example.

So now I am to create a full schematic. My thoughts (please challenge these!) are:

* Thermostat needs 12V/0.1A and TEC should have approx. 2.93V/3A. Hence, I need a power supply capable of providing 12V/3A.
* In order not to burn the thermostat, I need to reduce the current from 3A to 0.1A by adding a resistor R1.
* I need to add a voltage divider (using resistors R2 and R3) in order to reduce voltage for the TEC.

Have I made any mistakes (rather: what mistakes have I made?), or do my considerations seem fair?
Furthermore: Is the power going to be constant of 12V*3A=36W? Is there a smarter way of doing this to reduce price of components and consumption?

#### Dodgydave

Joined Jun 22, 2012
11,318
You don't need resistors, just supply the 12V 3 Amp supply to the thermostat, it will take what current it needs, if you need 3V and 12V, then an old Atx psu is ideal,.