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[#] Tue Jul 31 2007 15:11:19 EDT from Peter Pulse @ Uncensored

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Well, the losses they are talking about with distance to the ground etc is the capacitance between the power lines and the ground, which isn't really relevant to DC but is for AC. Also inductance of the lines becomes a factor in AC. Then there are probably radiation losses even though the frequency is low. The wavelength of 60Hz is measured in miles but with long distance lines that becomes relevant. But even with all these things taken into account, the regular rules of Ohms law still applies so to send the power long distances you need to jack the voltage up and then bring it down at the other end, whether it's AC or DC. But AC uses very simple technology to di it (simple enough that it was possible over 100 years ago) and DC can't. Right now the way DC - DC converters work (eg switching power supplies) is to convert the DC to AC at a high frequency, send it through a transformer (so they still use a transformer, just a smaller one) and then convert back to DC. Or they use a voltage multiplier circuit with capacitors, but that also involves switching.. so basically all these circuits involve using transistors to make the DC into something that isn't DC anymore...

[#] Sun Aug 05 2007 17:42:43 EDT from dothebart @ Uncensored

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 U=voltage (V) ,I =flow(A); r = Resistance(Ohm);  p = Power (W) 

u = r * i

p = u * i

and... p you can combine with t, than you have Ws or kWh in larger scales. 



[#] Sun Aug 05 2007 17:56:14 EDT from dothebart @ Uncensored

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also creating DC voltage by rotation is real error prone. while ac generators / motors don't have any electric contacts with rotation, dc ones must have. Converting Power in the size of MW from ac do dc or vice versa is technically impossible atm afaik.
 Electronic scales to trains atm. i think. So, a linear engine train like the Transrapid or conventional ones like the ICE or TGV can control their engine by electronic. Thats why they started to be able to cross european country borders in the 90'ies. German trains go by 15kV 15 2/3 Hz, french ones by 50 afaik. the 15 2/3 is 50/3 to make sense to the europeans using 50Hz AC allmost everywhere. I think till the late 80ies you had to have two engines to cross the border to french by train, or they swapped it at the border and pushed over by diesel engines.

[#] Sun Aug 05 2007 18:27:08 EDT from Peter Pulse @ Uncensored

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DC to AC requires an inverter or rotary converter. Not too simple. AC to DC used to be a problem but isn't anymore, because of advances in solid state rectifiers. For example the NYC subway system when first built used a system of rotary converters to go from AC to DC, strategically located along the train routes. But now those are all being replaced (or maybe, have all been replaced). At first they used tube rectifiers, now they are using solid state.

[#] Sun Aug 05 2007 20:15:24 EDT from dothebart @ Uncensored

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yes, a subway should be comparable to an ICE, though it won't go 300 km/H ;)

puting an engine/generator couple inbetween can't be that efficiant? 



[#] Mon Aug 06 2007 00:08:05 EDT from Peter Pulse @ Uncensored

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A rotary converter (motor-generator) is how they did it for over 100 years.

[#] Mon Aug 06 2007 10:40:13 EDT from Ragnar Danneskjold @ Uncensored

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Speaking of trains, I noticed that when the temps were in the 90's last week Metro North was running diesels..... I can only guess that it was to reduce the load on the grid....

[#] Tue Aug 07 2007 01:33:36 EDT from mightbme @ Haven BBS

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That explains an old photo of subway works I once saw. They didn't explain what the equipment was, but it was rotary and huge.

[#] Tue Aug 07 2007 09:25:40 EDT from IGnatius T Foobar @ Uncensored

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Here's a pretty good writeup (with photos) of rotary converters in use at the New York City subway system.

http://www.nycsubway.org/tech/power/rotary.html

(As a side note: nycsubway.org happens to be a site run by Dave Pirmann, who for a decade or so maintained the now-defunct "DaveCode" variant of our Citadel software. Small world...)

[#] Tue Aug 07 2007 10:21:56 EDT from dothebart @ Uncensored

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hehe, that subway article spawned an interesting discussion about CPS'es

which are motor/generator/flywheel/diesel combinations. but they can fail:

 http://valleywag.com/tech/breakdowns/365-mains-credibility-outage-282257.php



[#] Wed Aug 08 2007 03:53:40 EDT from 2Dog @ Uncensored

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Just confirmed: A new 32cc weed-whacker is in transit and should be here this Thur.

What happened to the first one? I dove into a patch of serious vines that wrapped
around the line head and stopped it cold at full throttle. The torque was enough to snap
the shaft and break the clutch. I called and said all I was doing was trimming the grass along
the sidewalk.

Since it was still in the unconditional 90 day money back guarantee period they sent UPS
out to pick it up and a new one is now on its way, and with no shipping charges either way.

I don't know if this belongs here or in the "Score" room. :^)



[#] Wed Aug 08 2007 13:35:31 EDT from Ford II @ Uncensored

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A rotary converter (motor-generator) is how they did it for over 100

years.

life was cheap.

[#] Wed Aug 08 2007 23:12:22 EDT from IGnatius T Foobar @ Uncensored

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Not that cheap. Rotaries required a paid staff to keep them running. Solid state AC-DC converters are a lights-out operation.

[#] Thu Aug 16 2007 14:15:48 EDT from Ford II @ Uncensored

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I bought a bottom freezer french door fucking huge refridgerator and a stove yesterday.
The fridge is fucking huge. It monopolizs my kitchen. But you can put tons of stuff in it.

[#] Thu Aug 16 2007 14:39:59 EDT from wizard of aahz @ Uncensored

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ford - How much Quick goes into that fridge??

[#] Fri Aug 17 2007 09:46:48 EDT from IGnatius T Foobar @ Uncensored

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None. Quik goes in the cupboard.

[#] Fri Aug 17 2007 10:11:22 EDT from Ford II @ Uncensored

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yeah, I've accidently put the quik in the fridge at times, doesn't help it any.

[#] Thu Oct 11 2007 16:29:28 EDT from IGnatius T Foobar @ Uncensored

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ummm... the right thing to do would be to dig around it, then cut it a couple of inches below grade. At that point you can attach a short length of new pipe with a joint on one end and a screw-on cap on the other. Then you put a box around the whole thing with an access plate at grade level.

Or you could just say "fuck it" and weld the whole thing shut and bury it.

[#] Thu Oct 11 2007 16:37:26 EDT from Ford II @ Uncensored

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I was going somewhere closer to option b.

A few months ago, I unscrewed the cap, went inside the house and flushed every toilet, turned on every sink and spigot in the house, and nothing went through that pipe.
It doesn't smell bad, so there's no noxious fumes coming out of it...
At the moment there's a sliver of cut around it, yes there's a hole, but it's not big, and I was too tired last night to do anthing about it.
I woke up this morning to happily find out there wasn't spooge all over my driveway.
So today I will cut off the rest except it's raining, and seal it over and be done with it.
I'm not going to weld it though, just epoxy or something I can pop off if I have to.

[#] Sat Oct 13 2007 23:21:22 EDT from IGnatius T Foobar @ Uncensored

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Today I decided to investigate a drip that's been coming from the gutter in front of the main part of the house ever since we had the roof replaced on that section.

There was a lot of water in there. And no wonder -- the stupid monkeys reinstalled the gutter with the slope pointing *away* from the downspout. And to think -- this contractor wanted to sell me new gutters.

The roof is fantastic, but there's no way I'd buy gutters from this guy now.

Actually, he spent a considerable amount of time trash-talking the PVC gutter we have in that location. Hate to say it but I actually like it better than the aluminum gutters -- easy to install and maintain, and it doesn't dent when you rest a ladder on it. I'll probably be putting more of them in.

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