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just call it 2 phase

Discussion in 'Electrical Engineering' started by [email protected], Feb 18, 2009.

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  1. James Sweet

    James Sweet Guest


    They have plenty to do with this discussion. The battery is low
    impedance and does tend to "hide" pulsing just like the B+ filter cap in
    the radio. As I mentioned, the hand crank radio would operate fine, even
    when the battery was old and completely worn out to the point that it
    would no longer take a charge. Anyone is welcome to try this, I see lots
    of speculation but no hands on experiments here aside from my own from a
    long time ago. Speaking of old car radios, most of them used a
    mechanical vibrator to generate the B+ for the plates, talk about hash,
    the crudest brushed generator would have a cleaner output than one of
    those still, with shielding and noise filtering, they worked.
    Additionally, if homes were fed by pulsed DC mains, they could be used
    to maintain the charge on a bank of batteries similar to the old 32V
    rural power systems in which batteries were charged by windmills and/or
    gasoline generators.
     
  2. James Sweet

    James Sweet Guest


    That wasn't my point. I was just saying that *if* for some reason AC had
    not succeeded and we still had DC generators powering our homes, radios
    could still be made to work directly from the generator, even generators
    build with mid 1800s technology.

    I didn't mean to imply that batteries need a pulsed voltage to charge,
    but simply that hypothetically if design constraints of the generator
    caused the output to be pulsed, it could still be used to charge
    batteries and power devices.

    In both cases I was simply countering arguments from someone else that
    this wouldn't work.

    Funny thing is with modern technology, DC power distribution would
    actually have some advantages, though in a residential situation the
    disadvantages of dealing with high voltage service and large DC-DC or AC
    converters would far outweigh the advantages, but it could be done. They
    use it in some long distance transmission lines afterall.
     

  3. It is actually becoming the preference.

    We could make a system for residential DC service with the batteries out
    at streetside. That is a chemical and environmental mess though.

    Until battery technology takes a few steps forward or until solar cell
    technology gets so good that we care less about battery bulk, we will be
    in an AC fed, AC consuming world. Make for easy conversion, but a
    magnetically noisy environment.

    DC makes for instant 'kill-n-cook' situations though. You really do
    fry.
     
  4. Don Kelly

    Don Kelly Guest

    Edison's machines were true DC machines. Some earlier machines were
    "Gramme Ring" machines which could have given you this impression
    (falsely). As far as I can see from pictures, his machines were drum
    armature 2 pole machines with a conventional commutator (which is a
    synchronous switch). Note that a commutator, properly used, switches the
    current only in the individual coils under the brushes, shorting the
    coils (2 in his case) on the neutral axis-at a time when the individual
    coil voltage changes polarity. During the time that the brush contact
    moves from one side of the coil to the other, shorting the coil in the
    interim, the voltage in that coil would be nearly 0. The total voltage
    would have little ripple as the rest of the coils would be
    producing normal voltage so the total voltage certainly did not go to 0
    or near 0. Brush width and material was a problem until it was
    discovered (by Brush or Thompson- I can't recall which) that carbon was
    ideal. Modern machines are designed to compensate for armature reaction
    which shifts the neutral axis and causes arcing. In Edison's day this
    compensation was done manually. In operation, except for considerable
    refinements in design, Edison's machines were essentially the same as
    modern DC machines.
     
  5. Don Kelly

    Don Kelly Guest

    By the time the "mains powered" radios came along, the supply was AC. In
    addition, while an arcing commutator produces hash, it produces more
    important problems in large DC machines and the design of the
    commutation system as well as proper maintainance of the commutator
    surface eliminates the arcing.
    Small motors such as used in drills do arc because a) nobody maintains
    the commutator until the arcing becomes a problem, and b) compensation
    for armature reaction is not provided.
     
  6. Don Kelly

    Don Kelly Guest

    Sure DC transmission has its advantages- at high voltages for long
    distances or for underwater or underground cables or for asynchronous
    connections between systems. All point to point rather than grid systems
    where specific technical requirements are needed or the distance is long
    enough that the savings in transmission costs exceed the costs of the
    end equipment. For mid level and distribution, it has serious
    disadvantages(no current zeros).- AC offers great advantages in
    switching and flexibility of networks and the optimization of voltage
    levels for the task at hand with relatively cheap and efficient
    transformers.
     
  7. James Sweet

    James Sweet Guest

    I read somewhere recently that the last DC service to a building in New
    York I believe it was, was shut off sometime in the 1990s. I had no idea
    it lasted so long.

    Somewhere there is a website with pictures of some of the gigantic
    rotary converters used to convert 25Hz AC to DC to drive subway trains.
    Some of these were still operational at least up to a few years ago.
    I've seen relatively recent pictures of polyphase mercury arc rectifiers
    still in operation doing the same job.
     
  8. Guest

    | A lot of transformerless tube radios were sold as AC/DC, and wouldn't
    | have worked if it was a Phil claims. You just had to make sure the
    | power plug was inserted the right way, or you got no B+ for the tubes.

    And these were plugged into Edison's DC system?
     
  9. Guest

    | The arcing commutator would generate so much hash that all you would
    | get would be a loud buzz. Any time the brush loses contact with the
    | armature, it arcs.

    And a filter that can remove 60 Hz (or whatever slow rate was in use back in
    Edisn's day) could not clean up some modulated noise band at higher freqs?
     
  10. Guest

    | If homes were still fed with DC, the generators would have to be a
    | couple miles from your home. Also, it doesn't have to pulse to charge a
    | battery.

    If using Edison's 220/110VDC split system, even a couple miles would be way
    too far. Today would could do transmission, distribution, service, and
    utilization, and different DC voltages and keep it DC all the way. It would
    still not be as cheap as AC, but it is possible to do.
     
  11. Guest

    | Sure, but do you want a 500 KV DC line directly to your home? ;-)

    Does anyone have a 500 kV AC line directly to their home? No.

    OTOH, 220VDC would bother me more than 480VAC.
     
  12. Guest

    | Some areas still had DC power well into the '60s and even early
    | '70s. A friend of mine in the Army told me what his dad had to go
    | through to get AC for the new elevator in his building near Chicago,
    | around 1970. The elevator company refused to repair the old DC model,
    | and only installed new AC powered elevators. People in those areas used
    | the transformerless radios on the DC power lines, and wouldn't notice
    | the switch to AC, as long as the usual two electrolytics following the
    | rectifier were still good.

    Some parts of West Virginia had 25 Hz into the late 1950's (my grandfather
    worked on those). It was there for powering coal mine equipment, but many
    businesses and homes were connected, as well.
     
  13. James Sweet

    James Sweet Guest

    Yes, some of them. Edison's system did not vanish overnight, fragments
    of it lasted well into the era of the transformerless AC/DC radio. As
    mentioned in a previous post, there were buildings in part of NY that
    were still supplied with DC until just a few years ago. One of the
    advertised features of these radios is that they could be run on either
    AC or DC current which was not the case with the safer and more
    expensive transformer sets before them.

    Useless but related trivia, the band AC/DC got their name from the label
    on the back of just such a radio.
     
  14. James Sweet

    James Sweet Guest

    They truly are a masterpiece of minimalist engineering. They cut every
    corner that could be cut in the name of reducing the cost. Packed
    components into the chassis however they would fit, wiring is a rat's
    nest, little in the way of shielding, and yet they do work, pretty well
    even, and many are still going fine a half century longer than they were
    intended to last.
     
  15. Guest

    | In article <>,
    | wrote:
    |
    |> Does anyone have a 500 kV AC line directly to their home? No.
    |>
    |> OTOH, 220VDC would bother me more than 480VAC.
    |
    | Why? Switching could be more of a problem with no zero crossings.

    That *IS* why 220 VDC would bother more to have it running through my home
    than having 480 VAC running through my home.


    | I have a 2400VAC line running along the property boundary line. I
    | suppose it would be feasible to have a dc to dc converter on poles to
    | distribute at the 110VDC level, but I do not expect that in my lifetime.
    | I do not think that I would want it. You might just as well have
    | rectifiers and switching supplies in the individual devices. That is how
    | all of my personal computers do it.

    I don't want that much DC coming into my home, especially with utility fault
    currents.

    I would draw the line at 600 volts for AC, and 48 volts for DC.
     
  16. Guest

    |
    | wrote:
    |>
    |>
    |> | If homes were still fed with DC, the generators would have to be a
    |> | couple miles from your home. Also, it doesn't have to pulse to charge a
    |> | battery.
    |>
    |> If using Edison's 220/110VDC split system, even a couple miles would be way
    |> too far. Today would could do transmission, distribution, service, and
    |> utilization, and different DC voltages and keep it DC all the way. It would
    |> still not be as cheap as AC, but it is possible to do.
    |
    |
    | Yawn. You could post something that makes sense, but you rarely do.
    | Lots of stupid things can be done, but why, other than to prove
    | someone's ignorance?

    So you don't really understand electricity, eh?
     
  17. Guest

    |
    | wrote:
    |>
    |>
    |> | The arcing commutator would generate so much hash that all you would
    |> | get would be a loud buzz. Any time the brush loses contact with the
    |> | armature, it arcs.
    |>
    |> And a filter that can remove 60 Hz (or whatever slow rate was in use back in
    |> Edisn's day) could not clean up some modulated noise band at higher freqs?
    |
    |
    | Did you even read what you posted? That is one of your most pathetic
    | attempts at trolling, to date.

    Do you even understand filters at all?
     
  18. Guest

    | In article <>,
    | wrote:
    |
    |>
    |> And these were plugged into Edison's DC system?
    |
    | That would do it. Did you ever work on one of those radios?

    I don't know if I have. I never had any DC of that voltage to plug any
    radios into. I did have some old radios that ran on 110VAC or so, but
    I only ever tried them on AC.


    | As an aside, IIRC, the dc motors were switched on and of by the
    | operators. Where only ac was available,the motors ran continuously. The
    | operator operated a clutch that connected mechanical power to the sewing
    | machine.

    Maybe DC would heat them up more?
     
  19. Guest

    |
    | wrote:
    |>
    |>
    |> | A lot of transformerless tube radios were sold as AC/DC, and wouldn't
    |> | have worked if it was a Phil claims. You just had to make sure the
    |> | power plug was inserted the right way, or you got no B+ for the tubes.
    |>
    |> And these were plugged into Edison's DC system?
    |
    |
    | No. They were plugged into the cigarette lighter of the flying
    | saucers at Area 51. If you are going to continue to post nonsense, I
    | might as well, too. :(

    I asked a question. Obviously you never provide useful answers.
     
  20. Guest

    |
    | wrote:
    |>
    |> |
    |> | wrote:
    |> |>
    |> |>
    |> |> | If homes were still fed with DC, the generators would have to be a
    |> |> | couple miles from your home. Also, it doesn't have to pulse to charge a
    |> |> | battery.
    |> |>
    |> |> If using Edison's 220/110VDC split system, even a couple miles would be way
    |> |> too far. Today would could do transmission, distribution, service, and
    |> |> utilization, and different DC voltages and keep it DC all the way. It would
    |> |> still not be as cheap as AC, but it is possible to do.
    |> |
    |> |
    |> | Yawn. You could post something that makes sense, but you rarely do.
    |> | Lots of stupid things can be done, but why, other than to prove
    |> | someone's ignorance?
    |>
    |> So you don't really understand electricity, eh?
    |
    |
    | Projecting your failings again, or just another pathetic attempt at
    | trolling?

    Actually, it is your inability to understand what you read that is a problem.
    In school, there was a subject called "reading comprehension". I guess you
    flunked that subject.
     
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