Posted by jnord 21 hours ago
I always thought AC’s primary benefit was its transmission efficiency??
Would love to learn if anyone knows more about this
To expand on this, a given power line can only take a set maximum current and voltage before it becomes a problem. DC can stay at this maximum voltage constantly, while AC spends time going to zero voltage and back, so it's delivering less power on the same line.
The transmission efficiency of AC comes from the fact that you can pretty trivially make a 1 megavolt AC line. The higher the voltage, the lower the current has to be to provide the same amount of power. And lower current means less power in line loss due to how electricity be.
But that really is the only advantage of AC. DC at the same voltage as AC will ultimately be more efficient, especially if it's humid or the line is underwater. Due to how electricy be, a change in the current of a line will induce a current into conductive materials. A portion of AC power is being drained simply by the fact that the current on the line is constantly alternating. DC doesn't alternate, so it doesn't ever lose power from that alternation.
Another key benefit of DC is can work to bridge grids. The thing causing a problem with grids being interconnected is entirely due to the nature of AC power. AC has a frequency and a phase. If two grids don't share a frequency (happens in the EU) or a phase (happens everywhere, particularly the grids in the US) they cannot be connected. Otherwise the power generators end up fighting each other rather than providing power to a load.
In short, AC won because it it was cheap and easy to make high voltage AC. DC is comming back because it's only somewhat recently been affordable to make similar transformations on DC from High to low and low to high voltages. DC carries further benefits that AC does not.
BTW, megavolt DC DC converters are a sign to behold: https://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jp...
There are many factors involved, and "efficiency" is only one. Cost is the real driver, as with everything.
AC is effective when you need to step down frequently. Think transformers on poles everywhere. Stepping down AC using transformers means you can use smaller, cheaper conductors to get from high voltage transmission, lower voltage distribution and, finally lower voltage consumers. Without this, you need massive conductors and/or high voltages and all the costs that go with them.
AC is less effective, for instance, when transmitting high power over long, uninterrupted distances or feeding high density DC loads. Here, the reactive[1] power penalty of AC begins to dominate. This is a far less common problem, and so "Tesla won" is the widely held mental shortcut. Physics doesn't care, however; the DC case remains and is applied when necessary to reduce cost.
- Three conductors vs two, but they can be the next gauge up since the current flows on three conductors
- no significant skin effect at 400Hz -> use speaker wire, lol.
- large voltage/current DC brakers are.. gnarly, and expensive. DC does not like to stop flowing
- The 400Hz distribution industry is massive; the entire aerospace industry runs on it. No need for niche or custom parts.
- 3 phase @ 400Hz is x6 = 2.4kHz. Six diodes will rectify it with almost no relevant amount of ripple (Vmin is 87% of Vmax) and very small caps will smooth it.
As an aside, with three (or more) phase you can use multi-tap transformers and get an arbitrary number of poles. 7 phases at 400Hz -> 5.6kHz. Your PSU is now 14 diodes and a ceramic cap.
- you still get to use step up/down transformers, but at 400Hz they're very small.
- merging power sources is a lot easier (but for the phase angle)
- DC-DC converters are great, but you're not going to beat a transformer in efficiency or reliability
now run that unshielded wire 50 meters past racks of GPUs and enjoy your EMI
> The 400Hz distribution industry is massive; the entire aerospace industry runs on it
nothing in that catalog is rated for 100kW–1MW rack loads at 800Vrms
> 3 phase @ 400Hz is x6 = 2.4kHz... Your PSU is now 14 diodes and a ceramic cap
you still need an inverter-based UPS upstream, which is the exact conversion stage DC eliminates
> large voltage/current DC breakers are.. gnarly, and expensive. DC does not like to stop flowing
SiC solid-state DC breakers are shipping today from every major vendor
> DC-DC converters are great, but you're not going to beat a transformer in efficiency or reliability
wide-bandgap converters are at 95%+ with no moving parts
Multipole expansion scales faster than r^2.
Also, im not in the field (clearly) but GPUs cant handle 2.4 kHz? The quarter wavelength is 30km.
"nothing in that catalog is rated for 100kW–1MW rack loads at 800Vrms"
Current wise, the catalog covers this track just fine. As to the voltages, well that's the whole point of AC! The voltage you need is but a few loops of wire away.
"you still need an inverter-based UPS upstream, which is the exact conversion stage DC eliminates"
So keep it? To clarify, this is the "we're too good for plebeian power, so we'll transform it AC->DC->AC", right?
"SiC solid-state DC breakers are shipping today from every major vendor"
Of course they do. They're also pricey, have limited current capability (both capital costs and therefore irrelevant when the industry is awash with GCC money) and lower conduction, and therefore higher heat.
They're really nice though.
"wide-bandgap converters are at 95%+ with no moving parts"
transformers have no moving parts. Loaded they can do 97%+ efficiency, or 2MW of heat eliminated on a 100MW center.
The skin depth by the way is sqrt(2 1.7e-8 ohm m / (2 pi 400Hz mu0))=~3mm for copper---OK for single rack, but starts to be significant for the type of bus bars that an aisle of racks might want.
As for efficiency, both 400Hz transformers AND fancy DC-DC converters are around 95% efficient, except that AC requires electronics to rectify it to DC, losing another few percent, so the slight advantage goes to DC, actually.
As for merging power, remember that DC DC converter uses an internal AC stage, so it's the same---you can have multiple primary windings, just like for plain AC.
I am a recovering audiophool.
I do own a pair of 2m long Monster Cable speaker cables (with locking gold plated banana plugs). I am fairly certain I've used welders with smaller cables.
(In my defence, I bought those as a teenager in the late 80s. I am not so easily marketed to with snake oil these days. I hope.)
(On the other hand, I really like the idea of a reliably stable plus and minus 70V or maybe 100V DC power supply to my house. That'd make audio power amplifiers much easier and lighter...)
What are you talking about? There's a very significant skin effect at 400Hz. Skin effect goes up with frequency. These datacenters use copper busbars, not cable, so skin effect is an important consideration.
You obviously need at least a dozen stands in parallel!!
Clearly skin effect scales with frequency but, 400 Hz is still low, only 2.5x lines frequency (the scale is by the root); so the skin depth is 3mm. 3mm on each side makes for a pretty hefty rectangular cross-section.
I'm pretty sure you have my delivery address from when I bought sorted Lego from you about 10 years back.
Let me know when to expect the 100,000Amp test equipment!
I shall make sure I wear better PPE than just my reading glasses.
:-)
Ah, that lego project... that was one I always wondered if I should have industrialized it but sourcing enough lego was a real problem.
That's low voltage lightning :)
Other people, of course, have other definitions of high voltage:
"This resonant tower is known as a Tesla coil. This particular one is just over 17 feet tall and it can generate about a million volts at 60,000 cycles per second."
and:
"This pulse forming network can deliver a shaped pulse of over 50,000 amps with a total energy of about 1,057 times the tower primary energy"
If there was anything like a high power transistor back then he would have used that. High power transistors that are robust enough to handle the grid were designed inly recently over 100 years after the tesla/edison ac/dc argument.
This!
The soon people realized these facts the better. The pervasive high rise buildings did not happen before the invention of modern cranes.
Exactly twenty years ago I was doing a novel research on GaN characterization, and my supervisors made a lot money with consulations around the world, and succesfully founded govt funded start-up company around the technology. Together with SiC, these are the two game changing power devices with wideband semiconductor technology that only maturing recently.
Heck, even the Nobel price winning blue LED discovery was only made feasible by GaN. Watch the excellent video made by Veritasium for this back story [1].
[1] Why It Was Almost Impossible to Make the Blue LED:
It accompanies in very low quantities aluminum and zinc, so it is extracted only in the mines of aluminum or of zinc, as a byproduct.
However, the abundance of gallium is similar to that of lithium, while gallium is used in smaller amounts, so there is no risk to not have enough gallium in the near future.
On the other hand, all semiconductor devices with gallium also use some indium. Indium is used in even greater quantities in all LCD or OLED displays, to make transparent electrodes.
Indium is an extremely rare element in the entire universe, comparable with gold, so for indium there is a much greater risk that its reserves will become insufficient.
This could be mitigated by extracting such critical elements from the dumped electronic devices, but this is very expensive, because only small amounts of indium are used per device, so very large amounts of garbage would have to be processed in order to extract a sizable amount of it.
(Gallium is a byproduct of aluminum production. We aren't going to run out.)
Unless by “make from something” else you mean extract the element from existing chemical compounds found in Earth, in which case we’re still just using existing deposits on Earth.
The earth's crust is 8% aluminum.
We will have bigger problems before hitting this one.
We will not remain without gallium, but it is impossible to scale up the gallium production to a higher level than provided by the current productions of aluminum and zinc.
So there is a maximum level of gallium that can be used per year and it would not be possible to increase the production of blue and white LEDs and of power transistors above that level.
Fortunately, the amount of gallium used per device is very small, so it is not likely that we will hit that level soon. A much more serious problem is the associated consumption of indium, for which the resources are much less.
The metal isn't going to disappear, but it won't be concentrated enough to be as easily retrievable.
I'm inclined to think we've lost that gold.
In your question you stated the running out as a given fact ("When" we run out, not "if").
If that was what you wanted to say I can't tell you, but that's definitely how it was received and thus you also got the harsh response. Since it reads a lot like doomsday thinking.
(Example: Does that mean when we run out of oxygen there are no more humans?
Why would we run out?)
You still seem to be missing the point.
If you talk about "when we run out", you are presenting yourself as an expert stating "we will run out" and asking about the aftermath.
It would be appropriate, and better received with more leniency, for you to ask whether we would run out.
Of oxygen, because of rising temperatures interacting with rock weathering binding all the oxygen.
Now, that's more of something to worry about at geological time scales, but Earth in fact, is not infinite.
Such predictions have an abysmal historic track record, because we tend to find workarounds both on the supply side (=> previously undiscovered reserves) as well as flexibility on the demand side (using substitutes).
This applies historically for oil, lithium, rare earth metals and basically everything else.
edit: I'm not saying we're never gonna run out of anything-- I'm just saying to not expect sudden, cataclysmic shortages in general, but instead steadily rising prices and a somewhat smoothish transition to alternatives.
But non-sustainable pricing is very different from "cataclysmic collapse", and too many people expect the latter for too many things, which is just not realistic in my view (and historical precendent makes a strong case against that assumption, too).
A society where water prices gradually increases to "reverse-osmosis only" (instead of "pump-from-the-ground-everywhere") levels is very different from a society where water suddenly runs out.
That's a classic example of the "preparedness paradox" [1]. When no one raises the alarm in time or it is being ignored, resources can go (effectively) exhausted before alternatives can be found, or countries either need to pay extraordinary amounts of money or go to war outright - this has happened in the past with guano [2], which was used for fertilizer and gunpowder production for well over a century until the Haber-Bosch ammonia process was developed at the start of the 20th century.
And we're actually seeing a repeat of that as well happening right now. Economists and scientists have sounded the alarm for decades that oil and gas are finite resources and that geopolitical tensions may impact everyone... no one gave too much of a fuck because one could always "drill baby drill", and now look where we are - Iran has blasted about 20% of Qatar's LNG capacity alone to pieces and blocked off the Strait of Hormuz, sending oil prices skyrocketing.
Yes we can run out of oil, but nobody really knows if or even when that will happen. Right now I'm guessing we won't run out because wind and solar is so much cheaper for most purposes everyone is shifting anyway - this will take decades to play out.
If you had made predictions/scenarios in 1850 based on Guano deposits running out within a decade or two, you would have mispredicted completely, because a lot of the industry just transitioned to sodium nitrate (before synthetic fertilisers took over). Nowadays media landscape would've gladly made such doom-and-gloom predictions for global agriculture back then.
I completely agree that quickly depleting reserves often indicate non-sustainable pricing for ressources (which is obviously bad long term), but that is very different from sudden collapse.
yyy! if we're going to wander off-topic :-) then I should mention elevators, water pumps, fire suppression including fire truck ladders and more! :-)
the podcaster Sebastian Major from "Our Fake History" did a looonnngg patreon episode on tesla and debunked most of the weird myths around tesla. Sebastian doesn't have a vendetta or anything, it's just amazing how much of the Tesla stuff is just nonsense or is viewed through a very weird bias nowadays. Major also briefly touches on the weird Edison stuff and how the internet has twisted Edison into a villain.
The funniest part is that The Oatmeal comic didn't invent this concept, but drew on pre-Internet narratives put forward by The Tesla Society, who were mailing busts of Tesla to universities around the country since the 70s at least. And that organization is explicitly nationalistic and religious, tied to other Serbian-American heritage organizations, and doing events with the Orthodox church.
So are many Serbs (more so if emigrants from atheist-socialist Yugoslavia, or descendants of folks who moved before WW2) as well as many other nations and organizations (America itself lol). So are many Something-Or-Other-American individuals and communities.
I presume that the organization(s) sending Tesla busts, being American-rooted, have had no illusions about which matters will forever remain impossible to communicate to Americans. (Such as anything not reducible to paperclip optimization.)
Instead, I consider it more likely that the point of promoting Tesla was not to impress anyone in America, but to uplift Serbia and generally the South Slavs of the Balkans who'd only gained national sovereignty in Tesla's day: "look, our heritage has already produced an honest-to-god American inventor half a jebani vek ago, so you guys have zero excuse to act as if you're stuck in the middle ages - do join the cargo cult of mordorn civilization instead, will ya - we got value to extract from ya!"
>They've basically projected the Jobs/Woz divide back onto two historical figures who, in reality, barely interacted.
I'd rather say this has been projected for them, but by whom is anyone's guess; not like there's a shadowy cabal operating. Besides said Serbian-American heritage promoters and whatever their game is, I guess - but here we're not talking mid-XX century Serbian diaspora any more, but a "culturally nonspecific" audience.
Much safer to call it "a hivemind situation" when nobody knows where some idea comes from, and nobody is accountable for rebroadcasting it either, since it comes pre-tagged as Good and True and Useful and it is wrongthink to doubt those. Especially when the idea is so obviously Useful for excusing nonaction. ("I can't be bothered to learn the first thing about electricity, even the history of why I have access to it in the first place - but now that Tesla guy I've vaguely heard of, he was the great genius of the people! What better reason to Experience a Positive Emotion!")
Aside from all the cult classics Keanu is part of like john wick and the matrix, even discounting that, he is a good person in it of itself who is genuinely humble and might be one of the best persons within hollywood.
What I feel pissed about is that people like Andrew Tate and others like them took the concept of Matrix and the contributions Keanu did within that movie and tried to capitalize on that cult classic decades after in the most toxic form that might be the issue if we are talking about an era
To be honest, Nikola tesla is also a great person within the context of his time. GGP's comment is still true but Tesla's contributions can hardly be reinstated and I'd much rather people believe these to be the heros (Keanu/Tesla) rather than Tate/Musk etc.
If I take anything from Keanu, I would like to take his humility/humbleness.
It always seems to me that the far right are bereft of original ideas and always co-opt other pre-existing concepts. There's exceptions, but I always find that right wing works are always lacking humour or irony (c.f. Ayn Rand's works).
That's not unique to them: Good artists copy; great artists steal.
- Oscar Wilde
If I was in his position I'm not sure I'd have taken it as well as he did.
enough Edison bashing!
Look, Tesla was a weirdo, but, he was a very good inventor who actually invented shit.
Edison was an industrialist, who knew the price of everything, and wasn't above spending a lot of money to destroy a rival.
Do I idolise Tesla? no, but I respect his understanding of high frequency electronics with really primitive tooling.
Do I despise Edison? also no, but he is a massive prick. Excellent buisness man, but an abrasive prick never the less.
IMHO, the vision he had about universal free electricity (transmitted wirelessly) was the dumbest. It was a novel idea, and he invested a lot (his time and other people's money) in it. The problem with his idea is that there was no way to monetize it (and profit from it). (There were also the technical issues of the power loss over distance (1/R^2), the harm to the environment, and the interference with radio communications.)
Edison was quite a villain. He stole many of his "inventions", and orchestrated a PR campaign against Tesla touting the "evils" of AC power. AFAIK, the electric chair was either invented or inspired by him.
I know these things because I've read many books on various topics related to Tesla, and all of this knowledge predates the Internet.
Thank you for quashing the gross misinformation. I was going to post this, but searched and found your comment. `\m/`
(I learned of the "Current War" in the 70's, since the Edison Museum was in my "backyard" -- and was a common destination of local school field trips.)
I only found Edison in the headline, I didn't find it anywhere in the body, nor did I find Tesla. Glancing through the article it almost seems like someone tried to make a catchy headline to get clicks.
You can have the best idea in the world, but if you cant manufacture it you're SOL.
Mercury arc rectifiers were used long before his death.
can we stop vibe generating headlines?
