Skip to comments.From Edisonís Trunk, Direct Current Gets Another Look
Posted on 11/20/2011 9:56:06 PM PST by neverdem
Thomas Edison and his direct current, or DC, technology lost the so-called War of the Currents to alternating current, or AC, in the 1890s after it became clear that AC was far more efficient at transmitting electricity over long distances.
Today, AC is still the standard for the electricity that comes out of our wall sockets. But DC is staging a roaring comeback in pockets of the electrical grid.
Alstom, ABB, Siemens and other conglomerates are erecting high-voltage DC grids to carry gigawatts of electricity from wind farms in remote places like western China and the North Sea to faraway cities. Companies like SAP and Facebook that operate huge data centers are using more DC to reduce waste heat. Panasonic is even talking about building eco-friendly homes that use direct current.
In a DC grid, electrons flow from a battery or power station to a home or appliance, and then continue to flow in a complete circuit back to the original source. In AC, electrons flow back and forth between generators and appliances in a precisely synchronized manner imagine a set of interlocking canals where water continually surges back and forth but the water level at any given point stays constant.
Direct current was the electrical transmission technology when Edison started rolling out electric wires in the 19th century. Alternating current, which operated at higher voltages, was later championed by the Edison rivals Nikola Tesla and George Westinghouse.
The AC forces won when Tesla and Westinghouse figured out how to fine-tune AC transmission so that it required far fewer power plants and copper cable.
DC didnt die, however.
AT&T adopted direct current for the phone system because of its inherent stability, which is part of the reason that landline phones often survive storms better than the electric grid...
(Excerpt) Read more at nytimes.com ...
The real reason for AC is to torture electrical engineering students.
This is all part of the windmill hype. The electric grid is the sustaining lifeblood of modern civilization, and these guys want to trash it for some kind of green steam punk vision. Don’t get me started.
Direct-current transmission is also better suited to handle the electricity produced by solar and wind farms, which starts out as direct current.
Um, solar sure. Wind farms (and pretty much all mainstream power sources) not so much, since they create energy by spinning an electromagnetic induction AC generator. So this part of the argument only works for solar, the most abysmally inefficient of all available sources. Hamsters on a treadmill are more efficient than solar.
I thought it was to torture live sound guys with 60 hertz hum.
That too. More than torture electrical engineers it is especially cruel to budding engineers from other disciplines who have to take basic electrical circuits as an engineering science elective.
Methinks that something got lost in the translation.
I always thought it was so the practical joker in the class (why are you all looking at ME?) could turn electrolytic capacitors into fircrackers by using a suicide cord and a wall outlet.
That’s the real reason. EE’s never feared E-Sci, as we called it. If someone was in the EE program and didn’t like E-sci, we told them to get out, because it was just going to get worse... much worse... when we got to Fields and Waves.
AC circuitry isn’t all that difficult to understand once you get the hang of complex math and lagrangian analysis of motors/generators.
I thought that was due to phones being relatively low power and all the central offices having battery backup.
Methinks that something got lost in the translation.
That part's true. POTS uses +24VDC TIP and -24VDC Ring.
Edison had an elephant electrocuted to try to get his picked.
The excerpt posted is so piss-poorly written that I won’t bother with the whole article.
The writer has no clue about electricity and nearly everything he/she said about what AC and DC is and does is wrong.
The reason AC was used is because you can step the voltage up and down as needed with transformers. You can’t do that with DC.
The reason you need to transmit power at high voltages is because power (watts) = Amps X Volts. If you double the voltage, you can get the same power with half the current (Amps). The reason this is important is because the higher the current, the higher the losses due to circuit resistance.
To simplify it greatly- you can use thinner wire to transmit the same power by simply increasing the voltage. High voltages in the hundreds of kilovolt range are stepped down by the use of transformers until they are stepped down to 220 and 110 volts for your household use.
You can’t do that with DC using transformers and so AC was adopted for the electric system.
Why reporters can’t just look it up before they write bullshtuff like this is beyond me.
It always reminds me of the time a TV news guy who was doing a report on a twin engine plane crash walks up to a mechanic working on a Cessna 172 or something like that and asked the mechanic “Will this plane fly safely on one engine?” to which the mechanic looked at the reporter with an “are-you-stupid” look and replied with much sarcasm in his voice “It flies best with one engine! It’s only GOT one engine!”
Reporters - it seems the only thing required of them nowadays is that they have an extreme left wing bias.
“I always thought it was so the practical joker in the class (why are you all looking at ME?) could turn electrolytic capacitors into fircrackers by using a suicide cord and a wall outlet.”
They took all the fun out of when they started scoring the tops of the cans with an X. Now they just go “PHHHSSSS”.
Not if you blob some solder on the top of the can first. Just sayin’.
I had a Model T spark coil. Great for creating a high voltage arc. Excellent for charging a Sprague Orange Drop capacitor. The go "snap" in the palms of unsuspecting folks. Also lots of fun if you fancy the Star Wars "light saber" accomplished with a fluorescent tube glowing from the spark coil. Even better if you have the patience to construct a sizable Tesla coil. Little "fingers" of electricity arcing all the way to the walls (while the foolish sat out in the hallway to watch).
Not sure what you mean by this. Hamsters may be considered as solar powered devices based on consumption of photosynthetically produced fuel. On what basis would they be compared to a solar cell? It seems to me that a solar cell provides about the most efficient imaginable conversion of the solar flux to electric power, on the basis of square footage of exposure. The hamsters require not only the agricultural square footage for their food ( in itself presumably much greater than the requirement for solar cells of equal output, ) but many ancillary fossil fuel based inputs, so that the net efficiency of a hypothetical hamster based electric power system would be, as one might suppose, ridiculously abysmal.
****If someone was in the EE program and didnt like E-sci, we told them to get out, because it was just going to get worse... much worse... when we got to Fields and Waves.****
Designing circuitry on a micron level that includes the elegant dance with Fields and Waves has worn out many calculators. An ever changing field that requires constant study and diligence.
I was a radar tech in the Corps. For fun we would hand a few florescent tubes to the new guy and tell him to stow them in the radome. More often than not they’d drop ‘em when the antenna swept by and lit them up.
How do you get it to stick to aluminum?
Spoken like a man who's never tried to maintain acres and acres of hamsters.
I have absolutely nothing to back up my hamster statement, as it was intended merely as a facetious jab at solar power.
That said, current technology photovoltaic cells typically achieve a mere 12% efficiency rate, meaning it literally takes a ton of them (and a correspondingly large chunk of real estate, manpower, and energy-intensive manufacturing processes) to produce anything approaching viable amounts of energy.
Dunno. Never tried; I went from practical joker to annoyed mentor long before they added the pressure release slots. I suppose you could plate it with zinc and nickel first but that seems like a lot of work just to make a little 'pop'.
AC is bad. It can electrocute elephants and sh&*ts.
Lots of rosin and a high wattage soldering iron.
But what about Global Warming and the Environment?!!
"Alstom, ABB, Siemens and other conglomerates are erecting high-voltage DC grids to carry gigawatts of electricity from wind farms in remote places like western China and the North Sea to faraway cities."
So I don't know what the technical implications are here. It just seems to me that the variability of wind produced electric power is a killer. The whole technology of the electric grid is oriented around stability, and we all have read the stories about cascading outages. It seems to me that the rhetoric of "smart grids" and rehabilitated DC power transmission is wishful thinking.
48 VDC on the line but 96 PDC ring voltage. I'm not certain how it is done now but they used to use a ring generator to put out the 96 PDC. PDC meaning pulsating DC current which would allow the old style Bell phones with bell ring and a capacitor across the bell it to ring.
There were several good reasons for DC on phone lines. First is noise. DC doesn't produce A/C hum. Second is the older switching systems were mechanical relays. Big huge bays of them. To avoid their lines from picking up A/C hum the wires both in the cable on the pole and even the phone wires in the home are actually twisted across each other. That is why you should use phone station wire and not thermostat wire too hook up a phone jack.
That was also part of the reason. The power source was independent of the power grid in event of emergency. The older system had huge batteries and a generator generators depending on the office to charge them in event of power failures.
When MA Bell began converting over to electronic switching in the 1970's this also cut down on the batteries needed. Before then the switching office for even a long distance office in place like Ashville, Nashville, Knoxville, etc was about as large as a Walmart. That was just for the long distance hub for a given region in a state. The replacement was electronic which it and a back up system would fit in an average size living room.
Our solar pv system uses Enphase mini-inverters. One for each 240 watt panel. Much better than DC to one big inverter.
Ah, either you're really old or you slipped in a clever historical reference...
>>>The reason this is important is because the higher the current, the higher the losses due to circuit resistance.
At at these distances and power that means you save a tremendous amount of money using AC.
You’re right, the low standard of journalistic knowledge continues to amaze...
Ironically, Edison promoted his DC current (versus Tesla's AC) by doing a road show where he executed elephants.
I was not questioning that, rather I was questioning the assertion that the "inherent stability" of DC power as opposed to AC power was "part of the reason that landline phones often survive storms better than the electric grid"...
They use both AC and DC on the same phone lines for different functions. They use DC to register an off-hook condition and to power the carbon transmitters (microphones) and AC to operate the ringers. Later phones use the same DC to power the touch-tone electronic circuitry. It’s about simplicity, not stability.
That is a very strange statement.
DC's "inherent stability?" Why didn't the author simply say that they decided to run the central office phone equipment on DC because they could use batteries that way, thus obtaining the "inherent stability?"
And how did they charge the batteries? Why, with commercial power from the grid, of course. And which type of commercial power was best suited for charging battery banks? What do you know--AC, when transformed and rectified.
And even the “best for solar” is a canard. They have to step up the output of solar panels with what? AC technology (inverters). The choice of the type of output from the inverters can be either AC or DC; the fact that the panel output was originally DC is irrelevant.
It was really a plot to make it difficult for students to gain admittance to grad school, preying on their susceptance to fads, while impeding their progress, taxing their capacitance to learn, and overcoming their resistance to doing so.
Thanks neverdem. Photovoltaic arrays 100 miles on a side (four of those) can supply our needs (during the day), but produce DC. Weird coincidence.
I guess there's no way to get around AC.
Only a EE geek would find that funny...
Another virtue of DC.
The bigger problem is that some liberal arts liberal is going to Google “acres of hamsters” and somehow use this forum as justification for promoting the idea as a replacement for Solyndra. ;-) They will get it backwards, and then try to use non-performance as justification for doing it.
I'm in awe of double Es. My understanding of AC ends at right about this neighborhood:
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