Edison's biggest mistake

Discussion in 'General Electronics Chat' started by shortbus, Sep 8, 2011.

  1. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    Watched a History channel program last night called "Dark Matters". One of the segments was about when Edison and Westinghouse were battling over whether AC or DC would be the electrical standard.

    It came down to Edison killing animals with AC. Then he pressured the state of New York to executing a man in the first electric chair. Edison proposed ,as most of you already know, that AC was more dangerous than DC.

    My question is - Is Ac more lethal than DC, given that both are at the same voltage and amperage?

    I was always under the idea that AC, because of the zero crossing of the sine wave gave at least a small chance of letting go of a wire, to stop the connection. Read this some where as a child and have just always believed it. As an old fart now I'd like to know.:p
     
  2. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    At relatively high voltages (let's say 1000 volts, for now), DC is FAR MORE dangerous than AC, simply because it is nearly impossible to let go once the current is flowing. You were under the correct impression--it is easier to let go of a wire carrying AC, so therefore, it is safer.

    I'm not sure how far you read into that story about Edison proposing the first electric chair. He suggested AC be used, and of course, the guy would not die. Had it been using DC the criminal would have died very easily, but because AC was used, it took a long time.

    Have you ever seen The Green Mile? I imagine electrocution in an electric chair using AC would look a bit like the guy with a dry sponge under the headpiece. It would be very difficult for him to die simply using AC electricity.
    Der Strom
     
  3. Jotto

    Member

    Apr 1, 2011
    159
    17
    Tesla was smarter. As you can see DerStorm8 has Tesla as his avatar. Seems the ones that really were the movers and shakers are always forgotten. Tesla was way ahead of his time. The radio, the first wireless. Would Edison be famous today without Tesla? I seriously doubt it.
     
    DerStrom8 likes this.
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    The main reason AC is far better then DC is something called generically grouped as "copper losses," no matter what the metal of the conductors.

    For a given power load, it is far simpler to use a transformer to step up an AC voltage to an extremely high potential, and thus require less current in a long distance transmission. The wires used must have some finite resistance, so the higher voltage you use means less power being burned off in the wire from A to B, where A and B may be separated my thousands of miles.

    In many trolly (streetcar) systems a DC voltage was used in the system, 700 volts DC comes to mind. (Note the trolly company was often the power generating company, and some of these companies still exist as electric companies sans the transportation end AFAIK.) When the trolly line got very far (here just several miles) the voltage would be reduced enough such that the trolly operation was impaired.

    The solution was to use the reduced voltage to drive a motor which drove a DC generator to re-create the 700 volt power.

    I may be confusing trolly power with train power, as it is in my bloodstream that the Long Island Railroad uses 700 VDC on their third rail to run their trains. My Dad worked for them, and they had some huge substations around the network to convert the power company AC to their DC. Inside each station were several open air motor generator units, each perhaps 20 feet around, mounted thru the floor, half on the first floor, half in the basement. The station had an overhead crane to remove and replace any unit. The "first floor" was open for 3 stories.

    So they made 700 VDC, and when I get asked "at what current" I always answer "enough to run a train!"
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    On another tangent, I once ran across Tesla's patent for the transformer.

    It's so common today one can forget these were actually invented at some point, and were patented devices.
     
  6. CraigHB

    Member

    Aug 12, 2011
    127
    15
    Tesla was a one of the most brilliant engineers in history. The ironic thing is he never fully profited from all his work and died with a lot of debt. He contributed so much to to the practical science of electricity yet the average person has never heard his name. Edison is the one who gets all the recognition, but he wasn't half the engineer Tesla was.
     
  7. kcarring

    Member

    Jan 22, 2011
    38
    0
    I agree Tesla was an amazing inventor and it is very unfortunate he has been so stricken from the books. Bottom line is, though, he was interested in progressing mankind's understanding not USE of energy. He wasn't interested in becoming a billionaire. If he was, he would have very much hardlined Westinghouse & JP Morgan, and followed closely to their paradigm for profit and riches. He wouldn't have delayed and sidetracked experimenting with wireless energy; rather, he would have just done what his boss told him. If he was half as greedy as Morgan, and others, he'd have become the most famous and rich engineer EVER. He wasn't a greedy businessman that understood how to profit from royalties and the retardation of advancement. He lived his fate of choice, really.
     
  8. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    I agree that at higher voltages, DC is more damaging and more deadly for same voltage, current and time of exposure. But at lower voltages in practical cases, such as AC home power voltage 110-220 V range. I think AC is more dangerous. It can stop the heart a little more easily (lower threshold current) and it's harder to let go of something when the affected muscles contract (again lower threshold current).

    I doubt the off time is long enough for 60 Hz power, given typical muscle firing rates below about 10 Hz, but at lower AC frequency it could be a factor.

    For whatever personal perception is worth, I think the thing that helps with AC is that you have a better chance to use other muscles, that are not contracted, to help you let go. When DC is above a certain threshold, it hits you like a ton of bricks and disorientates you more. I once hit 400 V DC briefly, with just one hand and was totally stunned like I got punched by Mike Tyson. My hand was burned and my arm didn't feel right for 2 months. As another example, I once sat down on wet grass while holding an old ungrounded metal chasis sander with both hands. My hands could not release the sander. But, once I realized this I knew to stand up with my legs. Apparenly the flow was through my butt cheeks, not my feet, and thank God I was in good shape because I sat down with legs crossed, Indian style). Once up, I threw the sander to the ground. The same senario with with DC might have locked up my legs, or confused my brain to not do the right thing, and a long constant flow of DC is very damaging, even if it doesn't stop the heart. Granted my personal examples were at different voltage levels, but I'm not going to do any more experiments with that to find out for sure.
     
    Last edited: Sep 8, 2011
  9. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    In the tv show they showed the convict getting 1000V for 8 minutes and not dying, then hit him with 2000V for 13 minutes and he basically cooked to death.

    Edison later said that he regretted using electricity for execution and fought against the death penalty for the rest of his life.
     
  10. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    Both Edison and Westinghouse cheated Tesla out of money for the things he invented for them. The first AC lighting systems Edison refused to let Westinghouse/Tesla use the screw base for their light bulbs, so Tesla came up with a base similar to the pin style used on fluorescent bulbs.

    Supposedly after getting cheated Tesla didn't write down many of his methods to do things and took them to his grave.

    Most of what is attributed to Edison was only thought up by him. It was left up to his lab workers to figure out how to make it work, then he Edison patented it.
     
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Edison Vs. Tesla; who was smarter?
    AC Vs. DC; Which is better? which is safer?
    Inline 6 or V8? 4banger?
    Questions without answers? Questions with many answers?
    Google search returns a plethora of other forum debates just like this one.
    AC is more dangerous...NO DC is more dangerous...yeah but you can't let go of AC ....well you can't let go of DC either and plus it causes electrolysis of your blood.. oh yeah well AC bla bla bla...

    I think we can all agree they both are dangerous and should be respected....and that Edison was a smarter businessman....! SPARK! now lets see the fire commence....
     
    DerStrom8 likes this.
  12. Jotto

    Member

    Apr 1, 2011
    159
    17
    The government confiscated all his papers, so we really don't know what he wrote down or didn't. He was way ahead of his time.

    To bad he told JP Morgan what he was doing, he might have advanced his wireless idea further.
     
  13. Jotto

    Member

    Apr 1, 2011
    159
    17
    I agree both are dangerous. I kind of relate this to nuclear weapons. Russia had enough to destroy the world more times the US. But it really only takes once.

    I agree Edison had more insight on cheating people then Tesla did.
     
    strantor likes this.
  14. CraigHB

    Member

    Aug 12, 2011
    127
    15
    Good point that Tesla was not the businessman Edison was. Tesla was more interested in science than making money. I can respect that. Though, he did put an amount of fruitless effort into protecting patents so I don't think he was totally oblivious to making money.

    He did seem to waste much of his later life with wireless energy. Like Einstein and his unified theory, he devoted his later years to it with little success.
     
  15. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    I vote for Tesla...
    But AC and DC are both usefull and could be dangerous sometimes.
     
    DerStrom8 likes this.
  16. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    For the record I think Tesla was the superior mind, but I couldn't just jump on the tesla admiration dogpile, not my style. had to throw a turd in the punch bowl.
     
  17. John P

    AAC Fanatic!

    Oct 14, 2008
    1,632
    224
    Edison invented several familiar devices that lasted for decades (not much use for phonographs or stock tickers these days, movie film is still around, light bulbs are on their way out) but he had his errors too. DC current distribution was one, and iron mining and ore processing was another. Then he compounded that second error by trying to re-use the machinery to make concrete, and when there wasn't much demand for it, he invented one-piece cast-concrete houses, and when nobody wanted those, he tried concrete furniture. So he had his hits and his misses too.
     
  18. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    His first invention (well, the first one he tried to sell IIRC) was a automatic voting system for congress. Congress didn't want it. according to the documentary I watched "that was the first and last time he invented anything without consulting the marketplace first" - I guess not, now that I hear about all this concrete crap.
     
  19. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    AC is used because it is easier to transform to different voltages with good efficiency.
     
  20. tgotwalt1158

    Member

    Feb 28, 2011
    111
    18
    How electricity affects lethally when it is AC and when it is DC? Only a good medical practitioner may provide the comprehensive answer. But, lets discuss. When one is under electricution (god forbid), his/her body behaves like a resistance and so becomes an electric heater. What is affected most is the blood which starts burning and hence density and viscosity of the blood changes. Consequently, the supply to all body organs is disturbed specially to heart and brain. It affects the victim depending upon his/her general health, age, emotional condition and physical environment in contact to the body e.g. earthed feet, touching with metallic objects, wet place etc. Since, AC's duty cycle is lesser than DC, it generates less heat as compared to DC so is lesser lethal than DC in this respect. Also, due to frequency of AC, it keeps heart beating (Like a life saver high voltage shock machine) but cause bad affects upon the weaker parts of the body. Whereas DC, due to its full duty cycle burns blood more quickly and hence heart stop, brain damage and the disfunction of some particular muscles may occur more quickly as compared to AC. Also, vibrational AC jerks may provide the victim a chance to get rid of the electricution upon zero crossing AC cycle and upon his/her most defiant moment.
     
Loading...