Circuit analysis of hobby project: insulated wine cabinet with cooler

Thread Starter

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?

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Dodgydave

Joined Jun 22, 2012
9,205
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,.
 

Thread Starter

caje

Joined May 2, 2020
9
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