I was considering a project with a thermoelectric cooling module rated 60w and so obtained an AC power supply of output DC 12V and 4.16A. I'm very new to electronics so excuse me for the basic questions but would I have to place some sort of resistors in the circuit even though the power supply is below the 60w rating so it shouldn't exceed what the module can handle.
Also I needed to connect two 12v 0.2A fans to the circuit, but how would I wire these with the other module and what resistors would I need? Thank you in advance.
Best Answer
The fans can be connected directly to the 12v supply. This leaves 4.12-0.2-0.2= 3.72A for the cooler. So, to ensure the PSU isn't overloaded, the TEC + resistor needs to be no more than:
Resistance = Volts/ Current = 12 / 3.72 = 3.23 ohms
The cooler has a resistance of around 12*12/60 = 2.4 ohms. So the resistor needed in series with the TEC must be at least 3.23-2.4 = 0.83 ohms.
The minimum power rating for the resistor needs to be considered as well:
Say you choose a 1 ohm resistor. The total resistance of TEC + resistor = 1 + 2.4 = 3.4 ohms.
Therefore the current flowing through both is:
Current = voltage / resistance = 12 / 3.4 = 3.53 amps
So the minimum power the resistor must ba able to handle: Power = Current^2 / resistance = 3.53 x 3.53 / 1 = 12.5 watts
So in other words, you will need a particularly beefy 1 ohm resistor.