Whole house "battery" wiring/power...


On Sun, 04 Oct 2009 18:22:56 -0500, The Daring Dufas

<snip>
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 calm down.
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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.
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James Sweet wrote:

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
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wrote:

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
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Tom Horne wrote:

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
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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
snipped-for-privacy@shawcross.ca
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Don Kelly wrote:

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.
http://www.fas.org/spp/military/facility/kwaj.htm
TDD
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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.
--
Don Kelly
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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 airplane. :-]
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 consumption examples.
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 of.
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.
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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.
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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 ;)
cheers
Jules
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Jules wrote:

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.
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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 :-)
cheers
Jules
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AC/DC radio sets were still commonly available into the 50s though, in the UK.
The Mullard valve amplifier circuits book, 2nd edition 1960, had a circuit for a 7W AC/DC amplifier, which was first published in 1957.
Stuart
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The differences, both historical and current are fascinating from either perspective. I've had some extensive discussions with an EE friend over in Manchester and we're both learning something new all the time.
I don't think I've ever asked if there were ever DC rural systems over there. These were off-grid and typically had a bank of lead-acid cells which were charged by gasoline or steam driven generators or windmills. There were 32V versions of virtually every small appliance of the day. Radios, fans, food mixers, etc. They made sense when farmhouses were often miles from the next house and more miles to the nearest town.
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And most farmers were quite happy to tie to the grid when it became possible - helping to build lines as well-- lots of rural electrification co-operatives came into being in the late 40's. My father was involved (from the utility side) with the the first one in Alberta, Canada, and the farmers were more than welcoming. The old windcharger/battery systems worked reasonably well for supplying lighting and small appliances but weren't capable of handling the heavier loads around the farms.
--
Don Kelly
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On Mon, 12 Oct 2009 19:35:40 -0700, Don Kelly wrote:

Interesting stuff. I never knew they had any real off-grid networks; I'd only ever heard of local generation supplying single dwellings. Shame there doesn't seem to be much about all of this on the 'net.

Take out the 'old' and that probably still stands ;)
cheers
Jules
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wrote:

Edison went to great political lengths to discourage AC, even publicly electrocuting animals to show how AC causes heart failure where the equivalent DC voltage would not.
http://en.wikipedia.org/wiki/Topsy_(elephant)
As you know the very nature of DC required multiple grids and an endless supply of local generating plants, all of which Edison wanted to provide.
My relatives have a farm in central IL with a generating windmill, this farm only got on the grid after WW2. In the 1930's windmill manufacturers in the US were producing about 100,000 windmills a year for farms that had no access to electrical grids. It used storage batteries. Funny how the wind circle is now being repeated.
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wrote:

Edison went to great political lengths to discourage AC, even publicly electrocuting animals to show how AC causes heart failure where the equivalent DC voltage would not.
http://en.wikipedia.org/wiki/Topsy_(elephant)
As you know the very nature of DC required multiple grids and an endless supply of local generating plants, all of which Edison wanted to provide.
My relatives have a farm in central IL with a generating windmill, this farm only got on the grid after WW2. In the 1930's windmill manufacturers in the US were producing about 100,000 windmills a year for farms that had no access to electrical grids. It used storage batteries. Funny how the wind circle is now being repeated.
These farmers weren't on any off- grid network. Some had windchargers and some may have had generators but many were still without electricity of any sort. Windmills to pump water, kerosene lamps. and wood or coal for heating. The co-operative effort was to get connected to the grid at a time when there were few, if any, farms remote from towns that did have grid connections. This meant building a local distribution system and the utility providing the tie to the grid and operation of the system. The first case was in a tightly connected Mennonite "colony" and later ones were more general groups of farmers after the success of this one. In general rural (and urban) population densities were (and still are) lower than those in IL(about 1/10 the population in 5 times the area-admittedly mostly concentrated in the lower half (prairie/parkland)of the province ).
--
Don Kelly
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On Tue, 13 Oct 2009 07:59:28 -0700 (PDT), windcrest

But he was wrong, and DC kills as well. Including the onset of ventricular fibrillation.
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