Talk:2642: Meta-Alternating Current

And today, we are reminded that Randall used to be a physicist (or at least has a physics degree). Not worth mentioning in the article, but while inverters can't reverse each other, transformers can. (Has Randall done the transformer/Transformer pun yet as an excuse to mock the movies?) Nitpicking (talk) 11:10, 7 July 2022 (UTC)

I haven't picked up the physics reference yet. I see electrical engineering here. Randall strikes me as somebody who would study physics given the opportunit, though. It's notable that this webcomic started while Randall was in college, if I recall right. 172.70.230.75 11:58, 7 July 2022 (UTC)

Long distance links, especially those between separate unsynchronized grids, use high voltage DC. There is a 2,000-mile link in China running at 1 MV. Arachrah (talk) 11:32, 7 July 2022 (UTC)

That's because at great distances, relatively high frequency AC loses a lot of ("active" = actually useful) power as ... reactive power, I think (didn't learn the terminology in English, unit seems right though). A typical grid has a lot of generators and load. A long distance connection results in a phase shift according to the transmission time (speed of light in medium x distance) in about the order of magnitude of the AC period (usually somewhere between 1/10 to 1/60 seconds) wastes a portion equal to the sine of the phase shift angle (up to 90° = all of it) as reactive power. DC isn't quite as easy to use but on long distances there is no power loss to reactive power. 627235 (talk) 12:25, 7 July 2022 (UTC)

Let's face it, the thing should be called an alternator. Of course that name's taken as a redundant word for (electrical) generator. 627235 (talk) 12:26, 7 July 2022 (UTC)

It always bothered me that UPS battery backups take the wall AC and convert it to DC to charge the battery, but then have to turn it back to AC to send it to the computer, so the power supply can convert it to DC to run the thing. I picture some connector that goes directly from the UPS to the power supply so that if power is lost it can just pull 12V directly from the battery. Andyd273 (talk) 12:47, 7 July 2022 (UTC)

some UPSs do this. They normally power the computer directly from the input AC, but if there is a power failure, they use the battery to power the inverters and switch the output to the inverter. Other UPSs always power the computer from the inverter. They have the advantage that there is not even a milisecond time to start powering the computer. That can be better for some equipment, and that kind of UPS often costs more. It is also worth noting that in some data centers, they bypass the AC step and have one big DC power supply that directly powers the computers. WhiteDragon (talk) 16:49, 7 July 2022 (UTC)

NOT logic gates are also often known as inverters. An even number of those would indeed produce the same output as the (true/false) input. 108.162.242.58 16:03, 7 July 2022 (UTC)

“Further chaining this into more inverters/rectifiers would normally not be considered.” Well, if you take a DCC controlled model railway for camping, you get a second stage of inverter/rectifier. The power supply of the DCC control station usually expects AC input, so you invert the DC of the car battery. The PSU then makes DC for the control station processor, which is then made AC to generate a DCC signal. The locomotives always have a rectifier to get a DC power supply from the DCC signal (which is confusingly AC).

You get a third stage with another plausible trick: put the battery on a car battery charger, which converts AC from the camping site power grid to DC. Then use a locomotive with a (rarely used) BLDC motor, which confusingly needs an inverter generating AC. --172.71.94.181 18:01, 7 July 2022 (UTC)

The efficiency calculation is bogus. For the rectifier, the "efficiency" of 81% relates to voltage, not power. (See https://en.wikipedia.org/wiki/Rectifier). I don't know what the power efficiency is, but I do note that my computer's power supply is not glowing white hot.