"The Daring Dufas" wrote in message
...
Don Kelly wrote:

"windcrest" wrote in message
...
On Oct 6, 7:11 pm, "Don Kelly" wrote:
"The Daring Dufas" wrote in
...



Tom Horne wrote:
On Oct 4, 5:04 am, The Daring Dufas
wrote:
James Sweet wrote:

My suggestion would be for a 48 volt DC system. Plain
old telephone service uses 48 volts DC for battery and
PoE, power over Ethernet is usually 48 volts DC. The
wire size could be smaller than that for a lower voltage
system and the 78xx type regulators are very inexpensive
and come in a variety of wattage ratings for stepping
down the voltages. The technology to pull it off is not
exotic and can be done with all off the shelf parts.
Solar and wind power could integrate quite easily with
such a system.
TDD
And what would be the advantage? The 78xx series are linear
regulators,
they are in effect a regulated resistor that burns up the excess
voltage
in the form of heat. On top of that, they max out at 37V input at
which
point a substantial heatsink is required to dissipate the heat.
The end
result is FAR less efficient than even the lousy iron class II
transformers found in most wall warts and small appliances.
You could use a switchmode regulator to get decent efficiency,
but once
you've gone that route, you may as well just use 120V or 240VAC
since
the additional components required are trivial.
Solar and wind power can easily integrate with the existing grid,
with
the additional advantage of being able to sell excess capacity
back to
the utility. The cost of the special inverter is low compared to
what
the panels cost, and dropping all the time. This proposed DC
system is
just reinventing the wheel with something inferior to what we
already
have.
I was thinking about it as an off the grid system. I would
imagine that a single high current DC to AC converter in the
battery room putting out standard AC power to a home would
be more practical than trying to reinvent all the appliances
and gadgetry. Tesla won the battle for the power distribution
system and I'm glad of it. There are those very high voltage
DC power transmission lines. I'm going to have to read up on
them and find out why they're using DC. It's been 20 years
since I worked on any high voltage power distribution systems.
Have you ever used a wooden hot stick? Make sure it's dry.

TDD

DC Power transmission lines are used to rid the line of skin effect
and allow the entire cross section of the conductor to carry current.
They are as yet only practical for long haul point to point
circuits.

--
Tom Horne

That's what I read. My only experience with high voltage power
transmission has been installing buried conduit, setting transformers,
making connections and splices on 15kv coaxial underground cable.
Of course there was all of the other wiring on the low voltage side
of the transformer including the facilities wiring. What I find
fascinating about the long haul high voltage DC power transmission
systems
has to do with the changes in technology over the years to handle the
conversion of AC to DC then back again. The early mercury arc
valve systems have got to be a sight to behold. I can imagine a mad
scientist wearing super thick lensed glasses cackling in the
background.

TDD

Even a 5Kw 6 phase converter was a sight to see- looked like an octopus
with glowing arms and a bright spot dancing on a dish of mercury.
Seriously the advantages of DC transmission has relatively little to do
with
skin effect as conductors are typically ACSR with aluminum on the
outside
and steel inside- and, at these voltages are grouped in bundles. The
size
of the conductor has more to do with mechanical than electrical
properties.
DC transmission at high voltages is economical for long lines where the
reduced cost of the line exceeds the added cost of the terminal
equipment.
There are also some other technical advantages . This breakeven point is
at
a much shorter distance for underground or underwater cable. DC back to
back
terminals are often used where frequency differences (e.g. in Japan with
both 50 and 60 Hz systems) or stability concerns arise. They do have the
disadvantage that reasonable and economic circuit breakers for DC don't
exist and this means that the system is essentially point to point
rather
than through an interconnected grid. In addition, conversion from one
voltage level to the next is bloody expensive, awkward and inefficient
compared to the use of AC transformers.
At low voltages, even for relatively short distances, DC is not a viable
option.

--
Don Kelly

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Thats why Westinghouse beat Edison in the early days of deciding what
electical distribution system to use, Westinghouse (scientist) wanted
AC, Edison (who was more of an inventor than a scientist) would not
let go of his prejudice for DC. I still have an old AC/DC radio from
those days, when radios were sold to work on either distribution
system.

Westinghouse was an inventor, and entrepreneur (as was Edison) - who
recognized good ideas when he saw them and a way to get around Edison's
stranglehold on the electrical "lighting" systems. This was weakened
before Tesla, by Gaulard and Gibbs who invented the transformer (1886 or
thereabouts for the first AC transmission). - making long distance
transmission possible. polyphase machines invented by Tesla were the
icing on the cake, and 3 phase systems followed soon after. Edison
wanted to hang onto his empire- so fought tooth and nail against AC- he
had a good thing going. Tesla once worked for him but got shafted.
As for the radio- If I recall correctly, until the late 1920's all
radios were battery powered. Then AC/DC units came into use. Better
ones used transformers to get the various voltages, filament and plate
(replacing the old A and B batteries).
The typical smaller radios that were sold in the 40's and 50's would
work on DC as they did not have a transformer, and tubes operated on the
rectified line voltage, with tube filaments in series. This was done, not
with intent to use them on DC supplies but because they were considerably
cheaper to build but could have a hot chassis (safety? what's that?).

The history of those times is very interesting. An often ignored inventor
who thought things out before trying them (as opposed to the Edison
approach) , was Elihu Thompson.


When I was a kid, I got hold of an old tube type record player
that had a metal chassis, for some reason when I was playing
around with it on the back porch of our house, I got lit up. DANG!! This
was long before two wire cords had a wide bladed
neutral. With all the electrical devices I played with when
I was a kid, I'm surprised I ever survived.

TDD

---
Hey, you've got an old radio which has seen better days- maybe even missing
its case but still working - put it in the shop or better yet in the laundry
area. you might be lucky .
--
Don Kelly

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