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 didn’t 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 ...
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.
Cheers
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.
Yup....bat'ries.
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