Editing 2642: Meta-Alternating Current

{{comic
| number    = 2642
| date      = July 6, 2022
| title     = Meta-Alternating Current
| image     = meta_alternating_current.png
| titletext = It's always bothered me that you can't cancel out an inverter by putting a second inverter after it.
}}

==Explanation==
This is the sixth installment in the series of [[:Category:Cursed Connectors|Cursed Connectors]] and presents Cursed Connectors #120: Meta-alternating current extension cord. 

{{w|Direct current}} is a unidirectional flow of electrons from a power source to something being powered, through one or more conductors, before returning to the power source via one or more other conductors, thus completing the circuit. Batteries produce direct current.  It is commonly used in electronics applications, including computers. {{w|Alternating current}}, on the other hand, frequently reverses the direction of electron flow, and is commonly used for longer-distance transmission (such as from the power plant to an outlet).

This comic proposes a humorous ''Meta-Alternating Current'', which uses a series of adapters to "alternate" between DC and AC current along the length of a connector. This is absurd in part because typical {{w|power inverter}} efficiency is 90%, and maximum {{w|bridge rectifier}} efficiency is about 99% for 120 V,{{actual citation needed}} so an {{w|extension cord}} made in this manner would lose about 11% power (compounded<!-- ...need a better word for this, but it's very much related to compound interest. It wouldn't be 100% loss after nine steps, but ~91% loss, i.e. 0.90*0.99)^9 -->) per such pair. For the wire shown in the comic, with seven pairs, the efficiency would be 0.89<sup>7</sup>, which is 0.45, that is, 45%.

The title text bemoans that an inverter, which converts direct current to alternating current, does not work in the other direction, as a layman's interpretation of the word "inverter" might assume. Rather, a separate device, a {{w|rectifier}}, also pictured in the comic, must be used for this second conversion. (However, a similar circuit to an inverter may be used to rectify in a process called {{w|active rectification}}.)

Common understanding of "inverting" would be to turn upside-down, or reverse some aspect of the input. In mathematical contexts, the inverse of an inverse is the original object. For a DC power supply we might have supposed that what is inverted is polarity between the input and output, something that would be easily done at high efficiency by just 'crossing' (without connecting between) the wires coupling the inputs and outputs. Applied to AC, it would shift the phase by 180°. Two such cross-overs would indeed restore the original electrical supply.

In the conversion from DC to AC, it is instead an active circuit that ''periodically'' inverts, and then uninverts, the effective polarity – with a specific frequency, and usually a voltage conversion, to conform to some AC need such as using a car battery to power a standard household device designed and built for use on a mains supply. A rectifier is a nominally passive circuit that accepts either polarity (e.g. at any given moment of an AC phase) and produces a single definite polarity as output, possibly smoothed out by a buffering capacitance or with additional components to attain a given voltage and amperage.

It may in fact be the case that a campsite use of a rectifying device intended for home use (e.g. a standard phone charger that down-converts household AC to a given DC) requires it to be plugged into an inverter itself powered from a battery system (DC to AC), more inefficiently than a single converter (with the correct voltage/amperage re-regulation) might accomplish the task. Further chaining this into more inverters/rectifiers would normally not be considered and the final AC phase will have no bearing with the original, should that have any practical significance, though the frequency and magnitude ought to be sufficiently on-target.

==Transcript==
:[Above the drawing there is a header. Below the header is a chain of rectifiers and inverters. There are seven pairs of rectifiers (the smaller ones) and inverters (the big chunky ones). The first five inverters have arrows pointing to them from a label above the chain, whereas the last five rectifiers are labeled below the chain, but also with arrows pointing to them from that label. The chain starts on the left with a mains plug (type B), followed by the first rectifier. It ends with the last inverter, and a female mains plug (type B socket) to the right. Beneath the chain there is label for the connector and an explanation in brackets below that.]
:Cursed Connectors #120
:Inverters
:Rectifiers
:Meta-alternating current extension cord
:(alternates between AC and DC)

==Trivia==
*This comic replaced [[No One Was Hurt]] as comic 2642 after it was taken down from [[xkcd]]'s website.
**See why on that comic's explanation.
*This comic initially did not have a high-resolution (2x) image for high-DPI displays, making it look more blurry than usual on such devices (such as smartphones). This was probably because it was uploaded hastily to replace No One Was Hurt quickly. It has since been updated to include a high-resolution version.

{{comic discussion}}

[[Category:Cursed Connectors]]