It wasn't my idea to start with you idiot, it was
a discussion about possibilities. I'm so glad that
a world leading expert such as yourself would chime
in and share your dearth of knowledge. *snicker*
On Sun, 04 Oct 2009 18:22:56 -0500, The Daring Dufas
You sure "helped" it along.
It doesn't take a "world leading expert" to see that you're full of
shit. Common sense is enough. Like I said earlier, try thinking for
yourself sometime. Your neuron might be scared at first, but it'll
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.
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
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.
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
From my reading, the problem of capacitive reactance is also minimized
with the DC transmission lines. When I was at Kwajalein Missile Range
during the late 80's, I got the chance to explore the old phased array
radar installation on Meck Island. It had a room we called the
Frankenstein room which was the power supply for the old radar. From
what I was told, the way they were able to make that monster scan, was
to change the phase angle of the microwave beam. The Frankenstein room
looked just like a prop from a science fiction movie. I wish I still
had the pictures. Here's a link, look for Meck Island an you can see the
big building in the upper right. There are two pictures, one showing a
view of the missile silo or silos. I don't remember if there were two.
That too, and that is a major benefit. However, there is still a reactive
problem at the receiving end where it is necessary to have the capacity to
supply reactive. This will be dependent on load and the particular control
of the system as a whole. For long lines this will be less than what would
otherwise be needed to compensate for line capacitance.
YOU ARE SOUNDING LIKE AN IDIOT
HOW DO YOU SUUPLY REATIVE ?
YOU SHOULD COMMIT HAIKIRI
IT'S CALLED REACTANCE
AND I AM NOT GOING TO SHOW YOU HOW TO ACHIEVE THAT HERE NOR ANYWHERE
YOU WILL HAVE TO PAY THE PIPER DONKEY LIKE EVERYONE ELSE
OR JUST SHUT THE FLUX UP
I AM PROTEUS
Only the Navy with their ships and submarines make use of DC well. That
still doesn't mean that it wasn't one hell of a costly implementation.
DC is great... on anything miniature, like a scooter, or model
Supplying DC feeds that can push as much power as we are used to with
current AC settings in the home would not be easy, and homes are low
Even if we had compromised, and made AC to the pole, and DC into the
house, the DC part has a lot of pain in the ass required maintenance that
AC does not suffer from. Galvanic effects being the first one I think
OK, so we drop the HV down to about 600V on the local poles, and then
we rectify that and feed the homes? Sounds like a very high
maintainence/service oriented method.
Maybe if we could make a nice DC chopper that would let us step off DC
highs and Gnd lows.. kind of a psuedo-alternation.
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
On Fri, 09 Oct 2009 09:04:47 -0700, windcrest wrote:
Hmm, that triggered a memory. I used to have an AC/DC one from the '60s -
manual switch, and you could feed 12V DC in on the same power socket as
AC. I doubt something like that would pass H+S these days, never mind the
amount of people who'd try to feed it domestic AC with the switch on the
DC setting and fry the thing ;)
That's actually a bit different. The AC/DC radios he refers to use a
transformerless power supply with the tube heaters wired in series.
Yours likely wires the tube heaters in parallel with a vibrator to
supply B+ to the plates when running from batteries.
The worst offenders for radios being plugged into the wrong voltage are
32V farm radios. The old 32VDC rural systems used the same plugs and
receptacles as the 110VAC systems standard elsewhere, so it's common for
someone unknowledgeable to plug a farm radio into a 120V receptacle and
blow all the tube heaters.
On Fri, 09 Oct 2009 23:49:42 -0700, James Sweet wrote:
For sure - it just stirred some braincells, that's all. The particular
radio I remembered was an early (ish) transistor design - I think it may
have been a Grundig, but I can't be certain now. The 12VDC ability was
just to allow it to be run from a car battery whilst camping - I seem to
recall my folks having a (black&white) TV that could run from a car
battery, too, but I don't recall if it had a manual voltage switch like
the radio did.
Just struck me as interesting that it was (in theory) so easy to plug in
to AC (via the same connector) with the voltage on the wrong setting and
presumably cook the thing!
Well, I grew up in the UK, and it's been 240VAC as standard over there in
just about forever (well, near enough, Google tells me 1916) - although I
think some DC via private generation in big, isolated houses survived into
the 1920's. The historical picture in the US is a lot more diverse, it
seems (and more interesting because of it :-)
AC/DC radio sets were still commonly available into the 50s though, in the
The Mullard valve amplifier circuits book, 2nd edition 1960, had a
circuit for a 7W AC/DC amplifier, which was first published in 1957.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.