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from the you're-not-just-bored:-the-wall-clock-IS-slow dept.
Electric clocks on continental Europe that are steered by the frequency of the power system are running slow by up to 5 minutes since mid-January according to a news release from the European Network of Transmission System Operators for Electricity ('entsoe'). The transmission system operators (TSOs) will set up a compensation program to correct the time in the future.
Many electric clocks rely on the transmission system frequency to provide a source that minimises long-term drift. Quartz crystals have good short term stability, but dreadful long term stability, so plant and machinery that requires power to be turned on or off at a specific time each day without maintenance over a long period historically used clocks slaved to the power-system frequency, which is kept long-term stable by the system operators to prevent problems in power generation and transmission across national and supra-national grids - for example, attempting to switch supplies to generators that are not synchronised to the grid frequency can severely damage the generator.
It is normal for transmission system operators to allow the frequency to drop slightly at periods of high demand, thus slowing clocks, but usually, the frequency is increased during periods of low demand to ensure the long-term average frequency remains stable.
(Score: 2) by Grishnakh on Tuesday March 06 2018, @10:44PM (43 children)
This makes me wonder how well a power system based on DC would work, since you wouldn't need to worry about the synchronization problems inherent with AC. Now that DC-to-DC converters are relatively cheap and readily available (unlike in Edison's time), it should be perfectly feasible to have a DC electric power system with ~200V power at point-of-use, and higher voltage feeds running to buildings and feeding converters on each, and appliances powered either directly by 200VDC or using a converter to get a much lower voltage like for electronics.
Obviously, this isn't at all feasible due to inertia, I'm just wondering.
(Score: 4, Informative) by DannyB on Tuesday March 06 2018, @10:55PM (18 children)
DC would be great for many uses at the building level. One large DC power supply. Lots of appliances and electronics within a building powered by DC. But what voltage? Electronics wants low voltages. But a vacuum cleaner still needs a LOT of power, and even, say 48 v is going to require thicker wires for higher amperage.
AC can go through transformers. This makes it possible to trade off current for high voltages for long distance transmission of power.
The lower I set my standards the more accomplishments I have.
(Score: 2, Disagree) by BsAtHome on Tuesday March 06 2018, @11:00PM (13 children)
Holding your finger on a DC wire is a lot more dangerous than the same voltage at AC. Your muscles will "turn on" at DC and you cannot release the wire, whereas AC allows you to get away from the wire again.
(Score: 4, Informative) by Arik on Tuesday March 06 2018, @11:05PM (2 children)
If laughter is the best medicine, who are the best doctors?
(Score: 4, Interesting) by edIII on Wednesday March 07 2018, @02:33AM (1 child)
Too Late :)
This was well tested with a couple hundred thousand volts (comparable to a high setting on a taser) on an innocuous looking capacitor that somebody tossed me. It was a like a grenade that you couldn't pry out of your fingers with a crowbar.
I almost shit myself, and the contact point was my hands. Caught it with both of them in just the right way that it arced through my hands, arms, and torso. Nearly every muscle in my body seemed to respond.
Never test this at home. Unless you want to look over your shoulder for a few years :)
Technically, lunchtime is at any moment. It's just a wave function.
(Score: 5, Funny) by anubi on Wednesday March 07 2018, @10:59AM
Tossing a plebe a charged capacitor, or leaving a charged one in the box, was the standard initiation ceremony at the school I went to.
I still remember sneaking up behind one guy thinking I was going to discharge a 40uF/450WV electrolytic behind him.
I scared the hell out of him all right.
I had forgotten the can was common to negative, and I touched the file I was using to discharge it to the positive terminal first.
Wasn't too bright that day. I never knew I could make that kind of noise. Ahhh, the stupidity of youth.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 3, Informative) by c0lo on Tuesday March 06 2018, @11:29PM (7 children)
I don't think this is true, given that physiological muscle relaxation time (30-75 ms for half relaxation) is longer than half the period of the AC we are using (10 ms at 50hz).
We** are electrochemical beings, the reaction speed is governed by the mobility of ions in acquatic solutions.
---
**Well, almost all of us, @bot may begin to differ.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by edIII on Wednesday March 07 2018, @02:35AM (4 children)
All I can say with authority, is that you cannot let go of DC. I desperately tried. Boy did I try.
Technically, lunchtime is at any moment. It's just a wave function.
(Score: 2) by c0lo on Wednesday March 07 2018, @02:47AM
Sorry, I missed blockquoting what I don't think is true. What my reply comment was addressing is the:
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 5, Informative) by martyb on Wednesday March 07 2018, @03:51AM (2 children)
Wit is intellect, dancing.
(Score: 2) by c0lo on Wednesday March 07 2018, @07:26AM (1 child)
Learnt this in highschool.
It'll still be a painful experience and a potentially (or does 'voltageusly' fits better in the context?) dangerous one.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by martyb on Wednesday March 07 2018, @01:49PM
Agreed. Tapping a live wire with the back of your hand is probably still a bad idea if your hands are wet and you are standing in water.
Wit is intellect, dancing.
(Score: 2, Disagree) by Nuke on Wednesday March 07 2018, @11:20AM (1 child)
c0lo said :
The point is not that you have time to withdraw your hand in 10ms. The point is that DC makes the muscle pull only one way (which may be to grip the wire harder), whereas AC is "neutral" with regard to muscle pulling direction in that the current direction cancels out on average as far as muscle movement is concerned.
I used to work for London Underground railways which has fourth rail electrification at 600v DC. I worked on the track sometimes, and the way the permanent way gangers I was with put it (from some experience) was that the positive DC rail was "sticky". I never experienced it myself.
(Score: 4, Informative) by c0lo on Wednesday March 07 2018, @12:10PM
The fact that the current goes one way or the other is irrelevant for the reaction of the muscle - it will contract anyway, the current mobilizes out the Ca+ ions, causing the proteins in the fibrils to contract. [opentextbc.ca]
If the muscles that are closing your fingers are involved, you won't be able to loosen the grip no mater if it's AC or DC.
To make the matter worse, an electric tetanus can let the muscle contracted for some minutes [allaboutcircuits.com], until the Ca ions repopulate the plasma inside the cells.
The only difference between AC and DC - AC is worse, it causes variable degree of contraction (it "shakes" the muscle) and makes the electrocution painful.
The DC contracts the muscle and keeps it that way in a single go - this is why the "stickiness" description, the muscle is contracted to the max and keeps this way no matter what your mind try to command it to do.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 3, Interesting) by RS3 on Wednesday March 07 2018, @04:16AM (1 child)
Ah, um, sort of not quite. Enough AC and your nerve electrical system is overwhelmed and you have no control of anything. You may want to, but agony is all you can muster.
There is a range of current that will cause heart fibrillation. Some quick research shows lots of differing opinions on lethal current levels. https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html [ohio-state.edu] It's not an easy thing to test, and even if you could, some people are quite strong, and some ready to die without electric shock helping.
Above that range you might survive because it's like getting hit by an electric shock defibrillator https://en.wikipedia.org/wiki/Automated_external_defibrillator [wikipedia.org]. They hopefully get the heart back into synchronized rhythm using a controlled electric shock.
There's some talk that AC is more dangerous to the heart. I've always feared DC because you don't feel it as much...
(Score: 3, Interesting) by c0lo on Wednesday March 07 2018, @07:49AM
Speaking of variability of human physiology, there are persons who can can touch live wired to 500V or thereby; thick skin on the fingers and palm and no sweating in the same areas - over 700kohm hand-to-hand measured resistance. Met one of them, he was working as an electrician and not even him would work unprotected - 'what if a wire punctures my skin' he said when I asked him.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by Grishnakh on Wednesday March 07 2018, @04:34PM (3 children)
DC would be great for many uses at the building level. One large DC power supply. Lots of appliances and electronics within a building powered by DC. But what voltage? Electronics wants low voltages. But a vacuum cleaner still needs a LOT of power, and even, say 48 v is going to require thicker wires for higher amperage.
Something like 200VDC would make sense, or maybe even 350VDC. (In countries with 120VAC systems, the peak voltage is about 170V, and in 240VAC countries, it's about 340V, so my numbers are pretty close to what we already use.) Electronics would have to be converted with a DC-DC converter, pretty much like we already do (except we currently use AC-DC converters that are really more like DC-DC converters with a rectifier on the front).
AC can go through transformers.
Except we don't do that any more. We use switching power supplies and converters for everything now. The only place we still use transformers is at the electric utility, for converting tens of kilovolts to the 120VAC your house uses (using a neighborhood transformer), or for stepping up/down power for transmission lines. And these are going the way of the do-do as they get replaced with HVDC transmission lines.
This makes it possible to trade off current for high voltages for long distance transmission of power.
You should look up HVDC. It's a really new technology used for transmitting power over long distance. It's only been in commercial use since the early 1950s though...
(Score: 2) by DannyB on Wednesday March 07 2018, @04:53PM (2 children)
I was not aware of HVDC. My mention of transformers was in regard to high voltage AC transmission.
Yes, I understand we using switching power supplies. And maybe that is an effective way to step down your 200 or 350 VDC to a stable 12 V or 5 V for many common uses. Although real isolation from the the electrical outlet would desirable. So maybe a DC to DC converter as you say. But this introduces additional inefficiency.
All this talk of DC only would please Edison.
Tesla would be spinning in his grave. (which would generate an AC current.)
I'm a software guy. I don't remember which end of a soldering iron to pick up. So maybe I'm all wet (and grounded), but it occurs to me that what if you could have a 2-stage switching power supply. You switch the main 350 VDC to a capacitor, and as its charge reaches the "stage 1 voltage" (> 5VDC) you disconnect the main, then as capacitor discharges below "stage 1 voltage", it is re-connected to the 350 VDC power. Now during the period while this first stage capacitor is disconnected from the electrical line, it is then possible to connect it to a 2nd stage capacitor to keep it charged up to a stable 5V. This 2nd stage is another switching power supply. At no point in time is the 5V output ever electrically in contact with either of the 350 VDC input wires. There is probably some reason why this won't work or is impractical.
The lower I set my standards the more accomplishments I have.
(Score: 2) by Grishnakh on Wednesday March 07 2018, @06:43PM (1 child)
I was not aware of HVDC. My mention of transformers was in regard to high voltage AC transmission.
They've been using HVDC since the 1950s now. It's not new technology.
Yes, I understand we using switching power supplies. And maybe that is an effective way to step down your 200 or 350 VDC to a stable 12 V or 5 V for many common uses.
Maybe???? That's the ONLY way it's done now, powering any 12V or 5V (or less) system. Everything uses a switching supply now.
So maybe a DC to DC converter as you say. But this introduces additional inefficiency.
No, it doesn't (at least not any inefficiency that could be avoided in some other feasible way). Again, everything now uses a switching converter for stepping down 120VAC to whatever your small device uses. They wouldn't be doing this if it were inefficient. Efficiencies for these things are well into the 90% range. High-quality DC-DC converters are well over 95%.
At no point in time is the 5V output ever electrically in contact with either of the 350 VDC input wires.
Switching power supplies already do not have outputs electrically in direct contact with inputs, and many designs use transformers for galvanic isolation. Maybe you're thinking of those cheap little transformerless power supplies that you can implement with basically a diode and a couple capacitors. Really you should go look up switching power supplies and read about them before you talk any more, if you're worried about or interested in safety aspects, feasibility in modern power systems, etc. Wikipedia [wikipedia.org] has a decent article to start with, though it does look like it's a little dated in places to me.
(Score: 2) by DannyB on Wednesday March 07 2018, @09:29PM
What you say is interesting. I am clearly uninformed about switching power supplies. And HVDC.
The lower I set my standards the more accomplishments I have.
(Score: 3, Insightful) by BsAtHome on Tuesday March 06 2018, @10:56PM (6 children)
There is a difference for local and global distribution. Global distribution is only effective using very high voltages (keeps current down and therefore limits I^2R losses). The synchronization problem is simpler when you have an HVDC transport, which is employed several places. However, DC is very ineffective for local distribution because the losses for DC-DC and DC-AC conversion are higher than AC-AC transformations and it is a lot more expensive too. That is, until you hit your local server rack-space, where DC distribution is more effective (partly because of UPS simplification).
(Score: 2) by Grishnakh on Tuesday March 06 2018, @11:07PM (4 children)
However, DC is very ineffective for local distribution because the losses for DC-DC and DC-AC conversion are higher than AC-AC transformations and it is a lot more expensive too.
I'm pretty sure this is no longer true. AC-AC transformation requires transformers, which are large, heavy hunks of iron and copper, both of which aren't that cheap (esp. copper). DC-DC conversion uses semiconductors, electronic control circuitry, and not so much metal, mainly some relatively small inductors. Take a look at the power supply in any computer now; it's really a DC-DC converter with a rectifier for the AC side (which is why it doesn't care if you feed it 120VAC or 240VAC).
Basically, AC is obsolete thanks to modern power electronics. Your post sounds like it would have been exactly right circa 1990, but things have changed a lot since then.
(Score: 3, Disagree) by jdccdevel on Wednesday March 07 2018, @12:40AM (2 children)
I'm not an electrical engineer, but my understanding is that a PC power supply built that way works because the wattages required are relatively low, such that semiconductors can handle them without burning up.
Try running a whole house's, (or an entire neighborhood's!) worth of power through a cheap semiconductor and I'm pretty sure you won't even be able to find the pieces after it explodes.
I know high voltage, high amperage DC to DC is possible, but it's still very expensive. Economies of scale may fix that... but that is nonetheless the case today. And there's no escaping the fact that high-voltage, high amperage currents would be required to provide enough wattage to run a house.
Even something as simple as a switch will wear out faster when used for DC current (AC current reduces contact wear due to arcing.)
Saying AC is obsolete flatly ignores all the uses for AC power that primarily don't involve electronics. (Appliances, heaters, machine tools, welders, fans, etc)
(Score: 4, Interesting) by RS3 on Wednesday March 07 2018, @03:52AM
Actually PC power supplies are DC to DC switching supplies _because_ of the power required. An iron-core transformer that can handle 200-400 W (VA) would be quite large and heavy.
I'll put it in perspective: a typical house has 240V 200A service (some are 400A...) so ~50KW (or 100KW). A typical electric car motor is 150-250KW and is controlled by, yep, semiconductors, often handling 350-500VDC. So you could easily run a house on semiconductor systems.
In fact, that's why Tesla makes the PowerWall https://en.wikipedia.org/wiki/Tesla_Powerwall [wikipedia.org] - they're already making power storage: Li-ion batteries, and controllers that handle similar power levels.
(Score: 2) by Grishnakh on Wednesday March 07 2018, @04:25PM
I'm not an electrical engineer
This is the first problem right here. You're commenting on something you don't understand.
Someone else already responded pointing out that a typical electric car handles more power with semiconductors than your house does, so I won't comment on that.
Saying AC is obsolete flatly ignores all the uses for AC power that primarily don't involve electronics. (Appliances, heaters, machine tools, welders, fans, etc)
The reason for this is because we already have an AC power system, so those devices were designed for that. There's nothing inherent about AC that makes those things work better on it, given modern technology. In the past, many machines did indeed use AC motors that were cheap and worked well with the AC power system. But washing machines, for instance, now have ditched their AC motors and use DC motors (usually brushless DC 3-phase motors actually, which are in reality AC but you don't drive them with household AC power) which are electronically commutated and controlled so they can be run at different speeds and in both directions. Welders don't use AC directly either, they have to step it up or down, and be switchable between AC (of varying frequency, depending on what you're welding) and DC (aluminum, I believe, needs to be welded with DC unlike iron/steel). Heaters can be run with literally any kind of electricity, they're just big resistors. Machine tools again use variable frequency drives to run their motors at different speeds and directions. Some fans do use simple inductive or even cheaper switched-reluctance motors, but the cheap-o fans in your PC for instance are actually brushless DC.
There's really no reason I can see any more to keep using AC, except the obvious fact that we already have an enormous global power system that works that way so there's a huge amount of inertia.
(Score: 3, Informative) by RS3 on Wednesday March 07 2018, @03:34AM
I pretty much agree with you. I'll augment your post by saying: we had good efficient switching supplies in the 1970s, and they've gotten better and better ever since, due to better semiconductors (faster switching, lower "on" resistance). My only beef with them is the filter capacitor failures. I'm fully aware of the "capacitor plague" due to faulty / cheap / fake / poor quality, but even good low ESR caps have a limited lifetime spec. under heavy switching currents (due to design compromises).
(Score: 1, Insightful) by Anonymous Coward on Wednesday March 07 2018, @12:08AM
(Score: 2) by frojack on Tuesday March 06 2018, @10:56PM (1 child)
DC long haul power lines are becoming a thing, as large scale EFFICIENT converter plants are becoming feasible.
Lots of DC lines are used in offshore Wind Turbines because AC underwater cables are so lossy.
They put the converter stations on-shore to feed the grid.
No, you are mistaken. I've always had this sig.
(Score: 2) by RS3 on Wednesday March 07 2018, @03:54AM
HVDC has been a thing for a long time: https://en.wikipedia.org/wiki/High-voltage_direct_current [wikipedia.org]
(Score: 2) by number11 on Wednesday March 07 2018, @12:30AM (1 child)
And it did exist, of course. That was what Edison built in the US (cue nasty PR battle between Edison as a DC proponent, and Westinghouse/Tesla as AC proponents). And there were places (parts of NYC, at least) that had DC until the mid-20th century. Cheap (tube) AC-DC radios were common ("All American Five", nasty things, chassis was hot to ground, filament voltages selected to work all in series at 115V).
One negative to DC: power switches must be much beefier. AC quenches the arc, but DC tries to keep it going.
(Score: 0) by Anonymous Coward on Wednesday March 07 2018, @01:00AM
I was in a warehouse building near Boston Chinatown in the late 1970s -- the freight elevator was DC. When the DC service finally ended around 1980, the building owner decommissioned that elevator (building no longer used for heavy freight.)
(Score: 3, Insightful) by pendorbound on Wednesday March 07 2018, @03:48PM (12 children)
Pretty lousy actually. Do some research on the Edison versus Tesla distribution systems. DC has much greater voltage drop over line distance. DC generation required a power plant every few block in cities. AC travels through metal conductors much more easily than DC and can travel greater distances with less voltage loss. AC is also much easier to convert voltages using transformers. That makes it possible to transmit power at extremely high voltages which travel even better over metal, then step them down to more useful voltages near the point of use (IE the transformers on the poles / lawns near your house).
Here's some background: http://www.elp.com/articles/print/volume-80/issue-6/power-pointers/primer-on-transmission-ac-vs-dc.html [elp.com]
(Score: 3, Interesting) by Grishnakh on Wednesday March 07 2018, @04:07PM (10 children)
I'm an electrical engineer, so I'm fully aware of the principles of electric transmission and Ohm's law.
DC has much greater voltage drop over line distance.
You're absolutely wrong about DC having a greater voltage drop: AC has a *higher* voltage drop over long distances because it constantly changes between positive and negative, so for part of the time it's not at the peak voltage, but rather somewhere in-between (even at or close to 0V), and during those parts of the phase has higher losses. In addition, AC has a "skin effect" so it doesn't conduct over the full diameter of the conductor, though this isn't all *that* significant at only 60Hz (it becomes more significant at higher frequencies).
DC generation required a power plant every few block in cities.
This is because Edison didn't know how to make MOSFETs or IGBTs and how to make modern highly-efficient DC-DC converters with them.
AC travels through metal conductors much more easily than DC
Absolutely 100% wrong, it's the other way around.
AC is also much easier to convert voltages using transformers.
Absolutely wrong. Ask Apple or any small-device maker if they still use transformers in their chargers. You were correct 30 years ago; where have you been since 1985?
Honestly, I really wish people who aren't electrical engineers would just keep their mouths shut when these discussions come up. It's really annoying having to argue with people who have a layman's understanding of things and whose information is decades out-of-date.
(Score: 3, Insightful) by FakeBeldin on Wednesday March 07 2018, @05:25PM (1 child)
And I wish that those who have knowledge would point this out and help interested others to understand things better without telling them to shut up and that they ought to be barred from the discussion.
Alas, neither of us gets their wish.
(Score: 2) by Grishnakh on Wednesday March 07 2018, @06:22PM
And I wish that those who have knowledge would point this out and help interested others to understand things better without telling them to shut up and that they ought to be barred from the discussion.
When those people post authoritatively-written responses instead of asking questions, that's the kind of response they get from people who know better.
(Score: 3, Insightful) by tangomargarine on Wednesday March 07 2018, @05:31PM (7 children)
The couple times I've tried to look up voltages and amps and ohms and stuff on Wikipedia have given me massive headaches, so I'll just stick to my programming and leave the "fucking magnets how do they work" stuff to you EE types :)
IIRC the joke back in college was that EE was the hardest degree, at least mathwise. "You start out as a EE major, then you realize it's too hard so you switch to Mechanical. Then you realize ME is too hard, so..."
EE -> ME -> SE -> CS -> IT -> Business -> Liberal Arts
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by Grishnakh on Wednesday March 07 2018, @06:03PM (6 children)
EE isn't as hard, mathwise, as a real math degree. It's possible to get through without having nearly the level of math knowledge that a true math major gets. But it does seem to be the hardest engineering degree. But I do think that a good Physics degree is probably harder. You should probably put physics at the head of that list :-) Also, a good CS degree (note the "good" here, a lot of colleges have crap CS degree programs) should be very challenging with math too, since in the older/better schools CS is really an outgrowth of mathematics.
But yeah, while there's some great discussion from others who obviously are EEs with much better knowledge than me about power systems (my specialty was digital electronics and then I moved into software in my career), I guess I am getting a little tired of getting responses from non-EEs whose knowledge of AC vs. DC hasn't been updated since the days of the "Current Wars".
(Score: 2) by Geezer on Wednesday March 07 2018, @11:03PM
At the last place I worked we had EE's, ME's, and WE's....Wikipedia Engineers.
(Score: 2) by RS3 on Thursday March 08 2018, @01:50AM (4 children)
I'm not sure if you can say one study or major is absolutely harder. Some people have inborn talent, smarts, something that makes them good at one thing, but not so good at another.
Yeah, and to be fair, all of this stuff is changing so fast that it's hard to know what's right or wrong. It's easy to say that an active electronic (semiconductors) power supply is better than an iron / copper transformer, but semiconductors are much more electrically fragile. Of course they could be designed to be more robust, withstand shock, vibration, temperature extremes, electrical shorts and surges, but most things are designed to be a cheap as possible. Also you have to consider availability, flexibility, adjustability, reliability; tradeoffs in design, size, shape, weight, heat, etc.
(Score: 2) by tangomargarine on Thursday March 08 2018, @04:26PM (1 child)
s/harder/more mathy/ if you like.
I don't think most people enjoy doing really advanced math. Other than math majors, but obviously they're crazy ;)
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by RS3 on Friday March 09 2018, @12:23AM
Truer words were never spoken! What blew me away in EE school were things like Maxwell's Equations, Fourier / LaPlace transforms & analysis, Bessel functions, etc., that these nuts did this stuff long before humans had the electronic circuits that these equations describe. And hardware hackers hacked all kinds of stuff together, not having a clue about the maths. I'll use math to get an answer, but if I had all the time in the world I'm quite certain I would not come up with the RS3 sequence, or the RS3 simultaneous manifold equations. RS3 transforms, maybe. :-}
(Score: 2) by Grishnakh on Thursday March 08 2018, @05:06PM (1 child)
It's easy to say that an active electronic (semiconductors) power supply is better than an iron / copper transformer, but semiconductors are much more electrically fragile. Of course they could be designed to be more robust, withstand shock, vibration, temperature extremes, electrical shorts and surges, but most things are designed to be a cheap as possible. Also you have to consider availability, flexibility, adjustability, reliability; tradeoffs in design, size, shape, weight, heat, etc.
Right now, with current technology, active switching power supplies *are* better than simple iron/copper transformers. Fragility isn't an issue; large transformers have their disadvantages too. As you said, things can be designed to be more robust, resist shock, etc. For shock and vibration, for example, lower mass is an asset; a heavy transformer has much more inertia. Anyway, things may designed to be economical, but they're also designed to conform to standards, and also to be robust enough to last a decently long time so the mfgr doesn't get a warranty claim. The proof is in the pudding: who's still using large transformers? Almost everything has switched to the switchers. And a lot of devices, at least, are lasting longer than they ever did.
(Score: 2) by RS3 on Friday March 09 2018, @12:04AM
I see what you did right there: "current"!
We can agree to disagree. I'll restate it my way: active switching power supplies *can be* better than simple iron/copper transformers.
I have no stomach for these endless online flame wars. You're entitled to your opinion, as am I. I don't like sweeping generalizations, and the use of the word "better" always catches my attention in that regard. I don't think there is a 100% clear absolute all categories winner. There are so many factors that go into a design, as I've stated elsewhere, that you have to consider all of the tradeoffs. In my personal experience I've found, and sometimes repaired, many many dozens of failed switching supplies (including electronic florescent ballasts). The only iron/copper transformers I can remember failing are recently made ones with thermal fuses embedded in the windings, which had failed (and they failed because the diode bridge on the secondary had shorted). I like semiconductors- been designing and building with them since, well, very long time. I just don't like the design compromises I find (Vceo too low, etc.)
Iron/copper mass can be a big problem due to the huge increase in unnecessary shipping roughness. I've repaired a couple of things (guitar amps, etc.) with badly bent chassis, transformer torn out of its screws, wires pulled out, etc.
(Score: 3, Informative) by khallow on Wednesday March 07 2018, @04:16PM
You also have parasitic loss due to eddy currents induced in nearby bits of metal. Polyphase systems [wikipedia.org] can greatly reduce these effects, but they never go away. Doesn't happen in DC lines except when first powering the line up.