I am reading up on logic circuits, families and levels because it's fun. I have no formal education in physics, computing or electronics.
For power supplies, sometimes one of the supply rails is referred to as ground (abbreviated "GND") โ positive and negative voltages are relative to the ground. In digital electronics, negative voltages are seldom present, and the ground nearly always is the lowest voltage level. In analog electronics (e.g. an audio power amplifier) the ground can be a voltage level between the most positive and most negative voltage level.
I know from previous reading, that electricity - at least when it comes to direct current, but perhaps even when it comes to AC? - has a way in ("line"?) and a way out ("neutral" or "ground"? - disregarding for a second the fact that ground also carries current in case of a ground fault).
Again, from previous reading, I know that we work computers by either supplying them voltage or not (or in some circuits a higher voltage and a lower voltage). In any case, it's a choice between one or the other, since that is what we are trying to represent: boolean true or false.
So, what is this "negative voltage"? Is this a figure of speech or can voltage actually have a negative value? The part from the article that I quoted above states in relativistic terms, that "the ground can be a voltage level between the most positive and most negative voltage level" (italic text by me), which makes me assume "yes". But if voltage is electromotive force, how can it be negative? I amusingly imagine a force "sucking" the current backwards. ๐คญ
Explain it to me as if I was five. ๐ถ
First, the DC voltage of these fans is a separate voltage system from the AC/mains of the house.
Whether the 12v comes from a transformer or a switching power supply, the DC and AC circuits are effectively separated by that device.
The ground of the 12v system exists only within that system (and is provided by the transformer/power supply).
Consider the tranformer/power supply to be a battery with a positive and negative terminal. Inside, a chemical reaction will take place that moves electrons from one set of plates to another, leaving "holes" in one set, and extra electrons on the other.
This creates an imbalance - an electrical potential - and entropy says everything should try to balance. So those extra electrons provide the voltage, and once a circuit is made, will immediately try to balance the potential by moving through the circuit to the other terminal.
Using a transformer/power supply provides those electrons (and a sink - somewhere for those electrons to return to) from AC/mains voltage.
This is a pretty simple way to view it, there are more details that an EE would take me to task for, but it's a good starting point.
This was great! Thanks!