How do I connect the wires on a PC Power Supply that supplies +3.3V, +5V, +12V, -12V, and +5Vsb to make 15 Volts for Peltier module?

Question

I've selected the Corsair CS450m as the PSU. I also found a 12V DC 30A 360W Switching Power Supply on eBay for about $54 AUD (I'm not allowed to show the link), but I wouldn't know how to get it to output 15V.

The Peltier Module is rated at as 15V at 8A (Using 60 Watts/h) and the heatsink (Deepcool Ice Blade Pro V2.0) has a 12V fan that uses 3 Watts (0.25A).

I also have a Ultrasonic Mist Maker to help cool the heatsink, through evaporation. Look for a video on YouTube titled: "thermoelectric Peltier TEC cooling with ultrasonic humidifier" to see what I'm talking about.

The mist maker is an AC device, so it'll have to use a wall socket.

The purpose of this, is to create an affordable water chiller for my Hydroponic DWC Reservoir, which needs to be kept under a certain temperature. To do this, do I need to cut the power to the PSU once the water reaches a certain temperature? How does a Temperature Controller turn off the power? Is there a way it can turn off both devices?

Answer 1

tl;dr: you don't want to run at 15VDC. Really. 12V is plenty.

There are a number of factors that come into play. To get the first one out of the way - as has already been said, you can't get 15VDC from a computer supply by using the -12V rail, and while it would seem to be simple to just use the +12VDC and the 3.3VDC rails in the same fashion, the fact that they have a common ground makes that not work. [One of the supplies will be a dead short. Not pretty.] The other thing to consider is what the efficiency curves say. Most, if not all, TEC will cool better at a lower voltage than maximum. Since you didn't give us the part number I can't check it, but using the 12708 (which looks pretty close to your stated specs) - running at 12V/6A is almost as effective for a lot less power (72W vs 112W). Remember, your heat sink has to reject all of the power you put into the TEC, plus the heat transferred from the cold side. You may find that the 40W difference matters. A lot. More is not always better. Use google to find the data sheet for your exact TEC (the number is on the "hot side") - you'll find you can run a bit lower on the voltage, and still get almost the same cooling.

Answer 2

You can't directly.

In order to get 15V from a PC power supply at any significant current, you would need a step up (boost) converter - a switching regulator to generate 15V from the 12V rail.

For very low current (~500mA), you can use the +/-12V rails to get 24V and then regulate it down, but you couldn't use that for your application because you would overload the -12V rail.

Alternatively (and probably most sensibly) buy a 15V PSU to begin with. Not much point going from 110/230V to 12V just to go back up to 15V.