Hobby Electronics Basics Still confused with basics

>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).
>
>Thanks Jay.

>To amplify JFs comments...
>
>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.

>On Sat, 21 Aug 2004 12:02:07 -0700, John Larkin
>
>

>>To amplify JFs comments...
>>
>>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.

>
>---
>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?

>On Sat, 21 Aug 2004 15:54:54 -0500, John Fields
>

>>On Sat, 21 Aug 2004 12:02:07 -0700, John Larkin
>>
>>

>>>To amplify JFs comments...
>>>
>>>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.

>>
>>---
>>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?

>
>
>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.