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Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

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Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#41

Post by yholio »

hexane360 wrote: post #26
repiret wrote: post #22

Earlier quoted context omitted.

That depends entirely on the voltage. AC won because transformers are relatively simple and can change AC voltage, but we can now build stuff to change AC voltage too.

Don't forget that three phase allows for three conductors to carry the power of three pairs of single phase conductors.

That's not entirely true. Any load imbalance on the phases is resolved through the null, connected to earth at both ends of the line. You can do the same with three single phase lines, although you wound need a massive earthing system with low resistance.

Or you could build a 2 wire (or 4, 6 ...) DC line with complementary polarity that would carry more power due to skin effects. If the negative and positive loads are balanced, the currents though the earthing wire cancel out.

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#42

Post by Tempest1981 »

walrus01 wrote: post #18
zuron7 wrote: post #17

Earlier quoted context omitted.

Transmission could be done via DC too, and there are quite a few benefits to it. The only field left to conquer is generation of electricity, looks like that's going to be in AC.

It is, but rather difficult and expensive for short to medium distances. Submarine power cables are often HVDC. https://en.wikipedia.org/wiki/Pacific_DC_Intertie

Cool! Which led me further down the rabbit hole: https://en.m.wikipedia.org/wiki/High-voltage_direct_current

- HVDC uses voltages between 100 kV and 1,500 kV.

- HVDC can be cheaper for 500+ mile runs

- HVDC allows power transmission between unsynchronized AC transmission systems

- Recent advances make UHVDC feasible (800kV+)

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#43

Post by aerovistae »

ajuc wrote: post #6

Similar prediction of ebook readers by Stanisław Lem in 1961 book "Return from the stars". He called them "optons". He also predicted audiobooks and called them "lectons". And Amazon :) > I spent the afternoon in a bookstore. There were no books in it. None had been printed for nearly half a century. And how I have looked forward to them, after the micro films that made up the library of the Prometheus! No such luck.…

That’s incredible.

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#44

Post by [deleted] »

wp381640 wrote: post #40

Bell had a video telephone demo at the 1964 Worlds Fair in NY[0] some five years prior to this NYTimes story I think a lot of public ideas of the future sprung out from that I don't think the quote refers to a portable telephone but rather of the style that was demonstrated at the World Fair [0] http://spectrum.ieee.org/geek-life/history/long-before-facet...

[deleted]

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#45

Post by yholio »

repiret wrote: post #22
garmaine wrote: post #21

Earlier quoted context omitted.

What benefits? The downsides are massive resistive losses.

That depends entirely on the voltage. AC won because transformers are relatively simple and can change AC voltage, but we can now build stuff to change AC voltage too.

Arguably, it's now cheaper in raw material terms to up-step and down step DC with high frequency transformers and buck-boost. The problems are lower efficiency than a modern, high efficiency transformer, which leads to increased dissipation and lower life of the complex electronics involved, requiring active cooling. An AC transformer is a well understood technology that can operate for decades without any maintenance. DC-DC high power convertors are exotic beasts with large downtimes and expensive to repair and maintain.

We are a long way of seeing this setup used outside very special applications, AC might no longer have a natural advantage but the benefits of DC are too small to justify the massive investments and research required.

Though, it can certainly be argued that a single home-wide rectifier and smart DC wall sockets could improve efficiency and safety. You could have things like negotiated power up, ground insulation, cheaper and more efficient light bulbs and appliances etc.

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#46

Post by devereaux »

aerovistae wrote: post #43
ajuc wrote: post #6

Similar prediction of ebook readers by Stanisław Lem in 1961 book "Return from the stars". He called them "optons". He also predicted audiobooks and called them "lectons". And Amazon :) > I spent the afternoon in a bookstore. There were no books in it. None had been printed for nearly half a century. And how I have looked forward to them, after the micro films that made up the library of the Prometheus! No such luck.…

That’s incredible.

I have always thought science is inspired by fiction.

Cellphones are nothing less than a better communicator, Bluetooth badges are even available on thinkgeek!

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#47

Post by tzs »

garmaine wrote: post #21
zuron7 wrote: post #17

Earlier quoted context omitted.

Transmission could be done via DC too, and there are quite a few benefits to it. The only field left to conquer is generation of electricity, looks like that's going to be in AC.

What benefits? The downsides are massive resistive losses.

Several are given in this Quora thread [1]. The main ones are:

• No frequency matching issues between systems.

• DC systems appears as an open circuit to AC systems, limiting the spread of faults.

• Less expensive towers and wires.

• No reactive losses.

• No line length limits. Apparently AC has problems with lines longer than half a wavelength (2500 km or 1500 miles).

[1] https://www.quora.com/When-and-why-is-DC-used-instead-of-AC-...

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#48

Post by Ruphin »

Tempest1981 wrote: post #42
walrus01 wrote: post #18

Earlier quoted context omitted.

It is, but rather difficult and expensive for short to medium distances. Submarine power cables are often HVDC. https://en.wikipedia.org/wiki/Pacific_DC_Intertie

Cool! Which led me further down the rabbit hole: https://en.m.wikipedia.org/wiki/High-voltage_direct_current - HVDC uses voltages between 100 kV and 1,500 kV. - HVDC can be cheaper for 500+ mile runs - HVDC allows power transmission between unsynchronized AC transmission systems - Recent advances make UHVDC feasible (800kV+)

Great excuse to get introduced to this wonderful engineering youtube channel (no affiliation) https://www.youtube.com/watch?v=DFQG9kuXSxg

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#49

Post by noobiemcfoob »

devereaux wrote: post #46
aerovistae wrote: post #43

Earlier quoted context omitted.

That’s incredible.

I have always thought science is inspired by fiction. Cellphones are nothing less than a better communicator, Bluetooth badges are even available on thinkgeek!

Inspired by or surfing similar waves of thought. Science fiction can just go further ahead, not bounded by the realities of science and production limitations.

Re: Some Day, You’ll Have a Telephone with a Screen and Be Able To Dial a Book

#50

Post by noobiemcfoob »

tokai wrote: post #15

I always have to mention Paul Otlet, when the topic of early predictions of technology comes up. Too bad he was all but forgotten. https://www.youtube.com/watch?v=hSyfZkVgasI http://www.doi-toshin.com/paul-otlet-s-vision-documentation-...

You should add more context to your comment
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