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ATX Power Supply Deep Dive

ATX Power Supplies are the main standard form factor for computers, and feature use cases out of the ordinary computer building community.


To understand where and how ATX power supplies may be used out of their domain we need to understand how they really works. ATX power supplies are what we call "Automatic Switching" this means that the power supply only will deliver the current the device needs. With other words it is possible to power devices that needs less watts than what the power supply is able to provide, as long as we follow a few simple rules.


Electricity in it self can be dangerous. Not only for people but also our devices. Understanding how you can use electricity safely is therefore our first priority. Reading on we will learn about the concepts of electricity.


AC is an acronym for Alternating Current. This is what we will find in our wall sockets. We call it alternating because it doesen't have a positive or negative pole that are consistent. In school you shall also have been learned that alternating current is the most dangerous.

DC is an acronym for Direct Current, unlike alternating current. Direct current will always flow from a positive to negative pole. While Direct current is not as dangerous as alternating current, causion is adviced.


When we talk about ATX power supplies these all have direct current as output, to really understand their use cases we need to know what their three main current leads are.
Current leads are the colourful cables that comes out of the power supply. Each cable deliver current, the basic ATX currents are 3,3, 5 and 12 Volt. For reference i've left a table with the currents and the lead colour below.

Ground 3,3V 5V 12V

Before we can use ATX power supplies for anything at all. It is very important to understand how we can put load on any of these leads, it's time for some math. I understand that math is not everyones favorite, but when we work with electricity one of the minimume requirements are simple math. Let's put up a formula as example.

All forms of current can be calculated, this is how power supply manufactors figure out what the maximume load on their power supplies should be. To calculate the load of anything really, we need atleast two factors. This can be Volt, Ampere or watt.


The formula for this will look like this 5V x 20A = 100W, we now know how many watts we can pull from a 5V power lead.
The same formula can be used on all the leads, voltage multiplied by amp.
This method can also be used to calculate how much load you can put on your wall socket. In Europa it's common to have between 220 and 240V in the wall socket, while on an 13A breaker. This will of course vary depending on where you are in the world.


The math to figure out how much you can pull from your wall is exactly the same. Voltage, in this case that is 240V multiplied by 13A which equals to 3120 Watt.


Now that you know how to calculate power from your wall socket and the ATX power supplies, the only remining task is to find a use case out of the oridinary.

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