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fartness
computersoc dot com
Premium
join:2003-03-25
Look Outside

AC/DC power

When electricity was becoming popular and installed in every home, why was AC power chosen over DC power? I believe homes were being wired with both at the time, but it seems AC became the standard.



John Galt
Forward, March
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Happy Camp
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3 recommendations

»en.wikipedia.org/wiki/War_of_Currents



whizkid3
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join:2002-02-21
Queens, NY
kudos:9
reply to fartness

Interestingly enough; I have found that many early 20th century buildings in lower Manhattan, which were some of the earliest to be wired for electricity - used DC power. At that time, the only equipment requiring electricity were the elevators and the lighting. (Computers and air-conditioners did not exist; and there were few appliances if any, to plug-in to a receptacle.) These buildings used DC power for many decades; with many still using the original DC elevator motors to this day.

AC won out; especially in the suburbs, because it was possible to use transformers to raise & lower the voltage and transmit the power cheaply over long distances.



Dustyn
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join:2003-02-26
Ontario, CAN
kudos:11
reply to John Galt

Read the whole thing... pretty fascinating stuff.



battleop

join:2005-09-28
00000
reply to fartness

The short answer is that you can "transmit" AC power over longer distances with smaller gauge wire. This means you don't have to have mini power plants ever 2-3 miles.
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fartness
computersoc dot com
Premium
join:2003-03-25
Look Outside

There are substations for AC, but I don't know in what amount they number.



battleop

join:2005-09-28
00000
reply to whizkid3

There are still lots of modern buildings that run on DC power today. We have a pretty decent DC plant in ours. It's rare to find a CO or Data Center that does not have a DC plant of some size.
--
I do not, have not, and will not work for AT&T/Comcast/Verizon/Charter or similar sized company.



battleop

join:2005-09-28
00000
reply to fartness

The required copper to send 200Amps that distance would be insanely expensive.



whizkid3
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join:2002-02-21
Queens, NY
kudos:9
reply to fartness

Found this to back up my story about Manhattan:

»cityroom.blogs.nytimes.com/2007/···-edison/

2007 is when Con Edison cut the last DC power distribution in NYC.

As for COs & data center having DC plants; its because battery back-up is DC. Yes, there is still DC everywhere. Its in the computers everyone of use are using at this time.


Bob4
Account deleted

join:2012-07-22
New Jersey
reply to fartness

Because it's easier to increase and decrease the voltage of AC circuits by using transformers, making long distance transmission more efficient.



Hayward
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1 edit
reply to fartness

Obvoiusly you never watch the History Channel or could even imagine Googling or Wiki.

AC won because of transmission posibility of hundreds of miles through transformers, vs fixed voltage DC that could only go a few miles.

Just google/wiki Tesla or Westinghouse.

The one time in his life Edison proved himself the rather bombastic arrogant IDIOT he could be, just because he had heavily (but not hugely and wouldn't be HIS) vested himself in DC and didn't want to trash it for a HUGE future, that mostly Westinghouse got, as Tesla had no business sense and died a pauper, again that EDISON could have probably as easily gotten is not so damn arrogant.
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public

join:2002-01-19
Santa Clara, CA
reply to Bob4

said by Bob4:

Because it's easier to increase and decrease the voltage of AC circuits by using transformers, making long distance transmission more efficient.

DC high voltage transmission lines are actually more efficient. Back when the selection was made, dc/dc transformers were not available.


Wily_One
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reply to fartness




Wily_One
Premium
join:2002-11-24
San Jose, CA
reply to public

Just think of all the wall-warts we wouldn't need if it was DC all the way...



Hayward
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4 edits
reply to public

said by public:

said by Bob4:

Because it's easier to increase and decrease the voltage of AC circuits by using transformers, making long distance transmission more efficient.

DC high voltage transmission lines are actually more efficient. Back when the selection was made, dc/dc transformers were not available.

The problem is generating high voltage DC where as you can easily make 100v AC into 10,000v (albeit at lower current until down converted again).... DC no matter what is what it is generated at PERIOD (unless you do an AC conversion) and line loss for DC is much higher.

There is no such thing as a DC to DC transformer with out some AC between.... an unshifting magnetic field can not be transformed other than resistively (and only down or burst capacitively up)... that's how transformers work its the AC acting as a rotating coil in a fixed structure and inducing electricity again static unshifting DC can't.

Your wall wart USB DC supply is transformed 120V AC, (25:1) reduced to 5VAC and then rectified to DC.

Now in most electronics circuits AC is useless other than power supply, and its all DC... but long line transmission is the thing AC does so well, and DC fails at.

If NYC were still all DC as it was turn of last century they would be power stations every 10 blocks not like 3 for the whole city.... That is how big the line loss for DC is... if you don't start at somerthing ridiculously BIG.

And another thing EDISON by EGO tried to do is say how DANGEROUS AC was.... by electrocuting both a Elephant and inmate with AC..of course no DC comparison....
Fact IS DC LOCKS your muscles can't let go if strong enough... the vibration of AC for an equivalant vlotage actually gives you the chance to let go if you can... again another stupid PURE GO EDISON thing leading to his lose and really credibility ever after... pretty much just retire after that, before proved stupid again.

Again astounding EDISON could be so EGO blind to it, though he had to see the science...unfortunately he didn't come up with and would get little income from, though likely would have considering how business dumb Tesla was... or altruistic depending on how you look at it... just wanting to give it to the world ... still died a pauper... should have been rolling in money, as those that capitalized on it did. (Like Westinghouse and even Edison (GE) finally)

And I actually take back that no DC to DC transformer thing ... you can induce a stepped up charge but you can not sustain it beyond a discharge before it must rebuild (like a capacitor fed off a DC circuit to store a back up punch) Why over driven audio amps crap out... the capacitors can't for that occasional big punch recharge fast enough... also why 500 watt amps are generally BS... yes they have the capacitor to intermittently deliver that big boom... but you demand that full time they turn it to what it is maybe 100 watt distorted crap.

Heck with copper wire and masking tape dual coil from a 9v DC batt built those shockers in school... up to maybe brief 100V zap but again they were basically a capacitor though do alter the voltage... but only stored burst not continuous... zapped you but then done until recharged.... feed by AC would be continuous big zap output, and the equivalent of todays stun gun.

Probably invented by someone that played around with masking tape momentously charged coils when they were a kid like I did, but had reason to say what if we do this (obviously from DC batteries but inverted to AC... kick your butt long duration) could be a non lethal weapon, instead of momentary practical joke.... hell wish I'd thought of that.

But never put near the condition to think of it but maybe they were.... just apply AC to a science oriented child's electronic joy buzzer practical joke.

Likely all it was.... and hey doesn't even need to be pure sinewave UPS... just X cycle pole shifting.... never even studdied them maybe even 25cps is fine forget our household 60 cps.

And again for years DC ignition coils were status quo but they again as basically capacitors can on recharge so fast but RPM going up.... led to new electronic methods... though digital not analog... so again get us away from physicality.

My childhood hand made momentary shock toy it today's AC (even if DC inverted to get there) powered stun gun... direct DC would never do it.

Again difference EDISON would never admit DC is DEADLY though that is what he tried to make of AC... in much PR

Problem is again equal voltage FACT is you have MUCH better chance of letting go of AC vibrating vs DC from 1st second locking you muscles.

Again makes you wonder how the Genius of the age EDISON could be so ABSOLUTELY EGO STIPID about it?

And pretty much went into retirement after for being that stupid... again having won WESTINGHOUSE big leaad for a while until EDISON gave, gave up and retired.

Wonder what else he might have done after if not so much never admitted retired... I mean that is how much tossed out the door by Edison Tesla was but really just stopped.

OK some refinement to phonograph deveopment but film really went to Eastman...basically after Teslas Edison gave up... something could be said of age... but not charachter.... he knew he was beat and age or not just gracefully faded away on his millions.

.

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Anonymous_
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reply to fartness

said by fartness:

When electricity was becoming popular and installed in every home, why was AC power chosen over DC power? I believe homes were being wired with both at the time, but it seems AC became the standard.

SO we Do not have 2 feet thick power lines overhead.
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Well, does your car at least turn into something else? Sometimes I turn it into a trashcan. Hmm...

Bob4
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reply to Hayward

»www.youtube.com/watch?v=VD0Q5FeF_wU


Edison was fond of electrocuting animals to show that AC was dangerous.


Hayward
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Key West, FL
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1 edit

said by Bob4:

(youtube clip)
was fond of electrocuting animals to show that AC was dangerous.

I believe I said that and profoundly wrong.... DC would have killed much faster.....

If not chained the AC elephant could have just stepped away likely.

Again the most stupid point in EDISON's life (I am sure he regreted) and NOTHING really ever after.... he retired semi in disgrace but for all he had done before. But really NOTHING after,,, that was the shameful end, but resting on his laurels.
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OK 1 of two thing happened here without reference....

Most obviouys no reference to sourse.... draw what evever... but you don't see source?

harald

join:2010-10-22
Columbus, OH
kudos:1
reply to fartness

DC has made a resurgence in recent years.

One of the limitations of AC is that the transmission lines act like radio transmission lines as they get longer. a quarter-wavelength of line at 60Hz is 775 miles in free space, probably about 500 in the real world. That's why the entire US cannot be tied into one grid. For long transmission lines, the load has to be matched to the voltage and the characteristic impedance of the transmission lines.

Los Angeles gets much of its electrical power as DC via two circuits called Path 27 and Path 65, also known as the Pacific Intertie.



Hayward
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reply to Anonymous_

said by Anonymous_:

said by fartness:

When electricity was becoming popular and installed in every home, why was AC power chosen over DC power? I believe homes were being wired with both at the time, but it seems AC became the standard.

SO we Do not have 2 feet thick power lines overhead.

And that comment has to do with ANYTHING?..... really you have two ft of concrete hanging in the air??? That sound rather scary
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Bob4
Account deleted

join:2012-07-22
New Jersey
reply to harald

Proposed 350 mile-long high-voltage DC line to be run from Montreal to NYC under Lake Champlain and the Hudson River:

»www.chpexpress.com


Kearnstd
Space Elf
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Mullica Hill, NJ
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reply to fartness

AC won because it is more efficient to step up and step down than DC ever can be.

these HVDC lines do a good job but they will terminate at a an inverter station and become AC again before reentry to the metro area part of a grid.

NYC Subway however is still DC. the MTA operates inverter stations through out the city.
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Bob4
Account deleted

join:2012-07-22
New Jersey

The northeast has railroads that operate on 25 Hz AC.


dmagerl
Premium
join:2007-08-06
Woodstock, IL
reply to Bob4

said by Bob4:

Proposed 350 mile-long high-voltage DC line to be run from Montreal to NYC under Lake Champlain and the Hudson River:

»www.chpexpress.com

So I'm just curious. How do they convert 1000MW of DC power to AC for eventual use? That's got to be one big honkin' inverter.. And how do they do it with any sort of efficiency.

BTW the Chicago El runs on DC. The newer cars though all have inverters on them and use AC motors.


SparkChaser
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1 edit

1 recommendation

said by dmagerl:

So I'm just curious. How do they convert 1000MW of DC power to AC for eventual use? That's got to be one big honkin' inverter.. And how do they do it with any sort of efficiency.

IF you Google HVDC, you'll find pages of links to info.


Hayward
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1 edit
reply to Bob4

said by Bob4:

The northeast has railroads that operate on 25 Hz AC.

Yeah actually as I recall that's what the NY/NH&H RR was into NYC Grand Central were, with their unique modified F diesel locomotives that had a 3rd rail shoe they could deploy, shut down the diesel and go all electric no exhaust into GCT. (600V comes to mind too)
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jameshell

join:2012-12-27
reply to fartness

Another difference among AC and DC occupies the value of energy it could carry. Each battery is intended to create only one voltage, and that voltage of DC cannot move extremely far until it starts to lose energy.


public

join:2002-01-19
Santa Clara, CA

1 recommendation

reply to dmagerl

said by dmagerl:

So I'm just curious. How do they convert 1000MW of DC power to AC for eventual use? That's got to be one big honkin' inverter.. And how do they do it with any sort of efficiency.

Efficiency is not hard when there are no restrictions on size and weight. Banks of thyristors driving an iron core transformer work quite well.
By the way a single 800kV DC line typically carries 8000MW, whereas three phase 760kVac carries only 3000MW.


J E F F
Whatta Ya Think About Dat?
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reply to Wily_One

said by Wily_One:

[att=1]

Yeah..that is what I was hoping too.
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If you can't explain it simply, you don't understand it well enough. - Albert Einstein