Since an electrical outlet might be used for any size appliance it must contain a full/max current and then the appliance only uses what it needs... right?
Does the appliance then reduce it? A simple lamp lightbulb uses very little but doesn't contain any electronics that would do this. So how does it use only a few watts and what happens to the rest?
Secondly, the electric meter and bill indicates watts used. How does this work? This seems to imply that the current is always flowing in and out like a two-way road and the meter measures the difference (unlike all the water analogies that flow into a dead-end).
Think of the power coming into your house as a rotating shaft. (Factories actually used to have one big rotating shaft from a water wheel or steam engine, and it ran everything.) If it spins freely with no load, no energy is taken and the power bill is zero. Any device can be connected to the shaft (they used to use belts or gears) and it can use all the horsepower it wants or needs. A mechanical device uses torque, and the power it gobbles is torque times speed.
An electrical system has wires (== shaft), voltage (== rotation of shaft), and loads take as much current (==torque) as they need. The price you pay is voltage * current * time * some_dollar_factor, because that quantity represents how much fuel the utility had to burn to make that much energy.
A low resistance load is like a high-torque load. It may even pull the line voltage down a bit, just like a big load might slow down the drive shaft some.
I like that better than the water pressure analogy.
Right, it's not a great mathematical analogy to AC. And a shaft has "inductance" (torsional flex) and "capacitance" (mass) but no equivalent of resistance, unless you make it out of taffy.
If you apply a sudden twist to a long shaft, it propagates just like a step on a transmission line.
I did design a mechanical full-wave rectifier once, so a ship shaft rotation indicator would count revs in both directions. It used a couple of shafts and some belts, and some really cool one-way mechanical couplings that look just like bearings and act like diodes. The MEs were impressed.
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Yeah, me too.
The only thing that isn't taken care of is the oscillatory nature of
the AC, which would correspond to an oscillating shaft coming into
your house. For heaters and lamps it wouldn't matter, you just grab
the shaft and friction does the trick, no matter which way it's going,
but to get the unidirectional rotation you need to run compressors and
simulate motors you'd need some kind of a mechanical converter. Maybe
like those little manually propelled railroad cars with the push-pull
bars used?
That is, voltage is the cause and current is the effect.
When you apply voltage to anything, the amount of current that flows depends on the resistance of that thing. That's why a big light bulb consumes more current than a little one. It has a lower resistance and lets the electrons flow through it more easily (thus grabbing more of them per second and giving off more heat and light).
Voltage = the pressure that makes electrons moved.
Current (amperage) = a measure of the number of electrons actually going by per unit of time.
The same thing that happens to the water that isn't coming out of your faucet when the faucet is turned on just a little bit. Those other electrons aren't flowing. Pressure is available to make them flow, but pressure is just pressure -- not flow -- if you don't let many of them move.
It indicates watt-hours. That is voltage times current times time. I.e., pressure times number of electrons that were actually moved through your house at that pressure.
It's as if the water company were charging you for the pressure of the water as well as for the quantity of it. That would be a reasonable way for them to charge you if you were using to turn waterwheels (rather than just consuming the water). The power company is charging you for the energy of the moving electrons, rather than for the electrons themselves, because you give them all back, exactly as if you were using water to turn waterwheels and then giving it back. They'd charge you for pressure and for the volume that flows by, because the product of these is the amount of energy you've received. (Not the amount of water.)
So an appliance built with low resistance takes more current and an appliance like a light bulb contains some material causing high resistance.
Regarding the meter... it's not measuring the difference between what came in and what's going out, but simply the flow into the house caused by some applicance usage.
If yes, then why do we need the neutral wire? Whats the extra wire leaving the house for? I thought I understood the loop concept.
Right. A light bulb with a fat filament will conduct a lot of amps (let a lot of electrons rush through) so use a lot of power and get very bright. A skinny filament throttles down the current to a trickle, so uses less power. If you weld ten skinny filaments together side-by-side, you make a fat filament that conducts 10 times as well. That's "putting resistors in parallel." Weld them end-to-end, and the current really trickles down, resistors in series.
Right. Actually it integrates the product of voltage * current. The voltage isn't supposed to vary much from 120, but the meter accounts for it anyhow, just to be accurate.
Current needs a loop, just as a shaft needs a foundation connecting the motor and the load to return the torque. Without a shared mechanical anchor for both ends, the motor or the load housing would just spin and no power would be delivered. We use the neutral wire as the reference or foundation to conduct the return current. We could (electrically and mechanically!) use the earth (ground) as the return path, but it's safer to use a neutral wire, and use the third (ground) wire as a safety shield.
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Don't you have it backwards?
That is, since mass fights anything trying to make it, or stop it,
from moving, isn't that like inductance, which fights tooth and nail
to keep any change of current through it from happening?
And isn't torsional flex like capacitance, which will absorb as much
energy as you can push into it until it starts to fill up and fight
back?
Also, doesn't it have resistance? No matter what you make it out of
it'll still get hot if you flex it, I think. Just like a cap has ESR
and a choke has winding resistance to contend with, a shaft has grain
boundaries which rub against each other and and spoil what would
otherwise be a perfect Q.
I just thought of another analogy... If you had a well connected to your water heater... you would be paying to heat the water, but not for the water itself.
My real objective was to understand enough to hook up a generator to the breaker box and reduce my bill. Transfer switches do the opposite of what I need... they work when the utility power is off and disconnect when the power comes back on.
I've also read someplace that home generated power isn't pure (?) enough to blend with the power company's. If so my only alternatives would be to use extension cords or a sub-panel for the few circuts I could feed (yes/no).
You MUST NOT connect your local generator in parallel with the power company!!!
You will need a manual transfer switch to transfer those circuits you want to power from your generator between the generator and power company.
"purity" isn't the problem. AC power is continually varying in voltage, so, if you want to connect two AC sources in parallel, you must ensure that both sources are "in phase" (varying exactly in step with each other) and of the same voltage.
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Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
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Actually, it's backwards from that in that when the utility power is
ON, that power actuates the switch and causes it to connect power to
the loads in your house. When the utility power goes off, the
transfer switch reverts to its de-energized position and a set of
normally closed contacts connect the alternate power source to the
loads in your house.
It's because your home service has *two* 110-volt circuits, which can be used individually for 110V, or combined for 220V. The neutral is the return for either/both of the 110V legs, and is not necessary for 220V.
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John Miller
Email address: domain, n4vu.com; username, jsm
Life is like an onion: you peel it off one layer at a time, and sometimes
you weep.
-Carl Sandburg
The electricity doesn't pile up at your house like water, or go into the light bulb and dissipate as light or anything like that. (not the electricity itself - its _energy_ comes out as light.) For the water model, it still comes in one pipe and goes out the other.
The energy gets transferred by the movement of the water. How hard does the power station have to push it (the pressure, or voltage) times how much it has to push (the flow == current). That force times motion is the work done, or energy transferred, and the power is the rate at which that energy is getting transferred. The water, or electric charge, is just the medium for moving that energy from one point to another.
What that probably meant is in connection with those systems that actually send power back into their system from your remote location and that in these cases the power company needs your generation facility to be "compatible" with theirs. Some power companies will make the meaning of "compatible" to be a nearly impossible goal to reach, just to be a pain. Some will encourage you and help you understand the details. But you can't just hook a generator up and start feeding power back into the lines without synchronizing up and without the right pieces in place. If all you are doing is to use your locally generated power to defray your own use and are NOT trying to push power back into the system of your provider, these issues don't arise.
I was working at a temp job as a document coder for big litigations. One of the litigations was about some company who was going to make a big profit that year that the government mandated that the power companies have to buy power from the customers. They had all kinds of schemes for excuses to generate power, like gas turbine generators with the exhaust used to heat a greenhouse, and crap like that.
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