|>| I think it comes down to a basic knowledge of physics. DC is coming
|>| into play again because people are installing solar and wind power
|>And maybe I need to consider that direction given the not so great level
|>of inverters I'm finding on the market.
| I know of lots of people, especially in the more remote and desert
| regions of the US that generate their own power. I am assuming you
| have checked out homepower magazine, which has been available on the
| web for years.
| http://www.homepower.com /
Yes. But I am doubtful of what they cover. All the systems people are
talking about in these cases are rather small. Considering the lack of
fault current issue I'm finding in inverters, it looks like I might need a
rather hefty system, even if I am going to cut back on the power actually
One target load is a full size electric cooktop with dual oven. I want to
rule out using gas on this (at least for now) because gas is a fossil fuel
and it need needs a tie-in to an infrastructure (pipes or trucks) in most
cases. Being able to do all my cooking on energy gathered renewably on the
property is a goal. Generating hydrogen to do that is a possible other
option to explore (and I would need to explore the viability and safety of
using hydrogen as a cooking fuel).
| Though I live in a suburb and will probably be tied to the grid for at
| least the next few year, I've enjoyed reading about the success
| stories that people have had with the German "Sunny-Boy Inverters" and
| others. Apparently, you can get into important but exotic subjects
| like what is the impedance of your utilities power transformer from
| the point of your service entrance.
If you want to sell power back to the grid, those might be a good choice.
But even those models come relatively small.
My original thought was to have inverters of a size needed to run the
cooking, and just duplicate that for other circuits, maybe 3 or 4 total
power segments. But with the low fault current issue, now it looks like
it might be better to gang them all together and target a very high end
level of current, at least enough to trip any branch circuit breaker.
The other extreme is to distribute DC and put inverters at point-of-use
without concern for the faults.
But in any case, an inverter must be able to survive a bolted fault,
even if it just shuts itself down.
|>So basically, it can be done for special cases, but it's not practical
|>for the common cases (at least not yet).
| Ok, I wasn't sure of your knowledge level. My background is an EE who
| works more with computers, but I've always had an interest in power
My background is CS but I took some EE classes, none of which were power
systems. My interest in power has developed over the past few years based
on sime issues that I've had with powering data centers. I found that if I
learned the electrical codes, I could specify circuits for large numbers of
computers without electricians coming back and saying something won't comply
with codes. It has expanded from there.
| Back in Edison's day, there were no sockets, dynamoes, wire,
| insulation, fuses, switches or meters readily available for sale.
| They had to practically build everything from scratch.
There wasn't a lack of knowledge. Electricity had been around for 80 years
by then, and electrical power had been commercially produced for many years
before Edison got involved in it, some AC, some DC. What Edison did was
make a big market for it. You couldn't just pick up some some insulated
wire at the corner store, but it was available from more than one
manufacturer. The science of the insulation was, though, still quite
| Yet, they were successful and the first DC Central Station came on
| line in the crowded Pearl District area of New York City in 1882. The
| voltage was 110 volts and the maximum distance for customer service
| was about one mile.
| Beyond that, you have the classic problem with DC. Even at this
| distance the mains had to use extremely large diameter wire... else
| the lights would dim out to zero output. One mile was about the
| maximum economical distance for a complete low voltage dc system and
| that is derived from the laws of physics.
It was actually a 220 volt system, in terms of how far it could be run for a
given amount of total power used.
| This leads to the story of the "Battle of the Currents", AC vs. DC.
| Tesla, Westinghouse, and the development of the electric chair which
| I'm not going to attempt to re-tell here, but you can certainly read
| about it from other sources.
Read that several years ago.
| What revolutionized AC was the invention of the transformer by Lucien
| Gaulard and John Gibbs in the early 1880's. Like the radio triode
| inventor Lee DeForest, these guys didn't really understand their
| invention very well and kept hooking them up incorrectly (in series)
| until other engineers stepped in to fix the technical problems. Like
| the birth of the electric chair, this itself is a fascinating story...
They effectively invented the current transformer :-)
Series, whether transformer connected or not, was a fundamental problem.
It did solve certain problems that make it useful in certain situations
even today. For example lights inaccessible to ordinary people can be
powered in series at an overall rather high voltage to maintain each at
the same current level. Parallel wiring leads to distant lights at a
lower voltage, so you can't just tweak the voltage to get them at the
level you want.
If you want to keep a string of lights at equal voltage over very long
runs, you might consider the method posted about half-way down in this
|>I have no such info. What I am wondering about is, if it would be possible
|>or practical to distribute power that stays DC all the way from where it
|>is generated to to the home/office. I guess the answers would be "perhaps
| Do you live within a mile of the power plant? Then the answer is
| maybe yes? Would they be willing to install DC generators just for
I think that's a "low voltage" issue rather than a DC issue. If there is a
way to step DC up to high voltage and then step it
back down, then "DC over one mile" is not an issue.
This is about low voltage ... and about DC not really being practical for
common voltage changing (yet). DC itself is not inherintly the cause of
this limitation; the fact that it can't be economically transformed is.
Solve that tranformation issue and DC works.
| Or. is your office a few miles from a coal mine or hydro plant? Then
| you could have point-to-point dc transmission at a higher voltage, but
| they might make you pay for all of the extra equipment needed.
AC is still the practical means to transmit and distribute power. That may
change some day in the future.
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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