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Old 20-04-2010, 20:27   #1
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Watts, Amps, Volts, Ohms ?

to make electrical systems less confusing, is there a way to compare watts, amps, volts, ohms to, say, a car's; horsepower, speed, fuel burn, fuel capacity , etc ? I know usually a river is used as a simile. thanks.
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Old 20-04-2010, 20:42   #2
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I've seen it done with plumbing; Volts being water pressure, Ohms is a measurement of resistance like a partially closed water faucet, amps is a measurement of water flow, etc. Is that the type of thing you are looking for?
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Old 20-04-2010, 20:42   #3
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The pipe analogy is the one I remember learning.

Current = the amount of water moving through the pipe. So something like 5 gallons / minute.

Voltage = the pressure of the water. So let's say 5psi.

Ohms = the drag / resistance of the water. Let's say it's a dirty pipe with a bunch of clogs in it.

Watts is about power, and you can express horsepower in watts. 1HP = 745.7 watts.
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Old 20-04-2010, 20:45   #4
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Another handy tip: voltage is what you can see and hear, in the case of humming and static discharges. It's things of two different potentials equalizing with eachother.

Current (amperage) is what will kill you dead. If you've ever been electricuted you'll know the feeling of a wave of energy that paralyzes your muscles and "flows" through you. Much different than the feeling of zapping your hand because of static on a door knob (which is voltage).
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Old 20-04-2010, 20:46   #5
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Volts = RPM
Amps = Torque
Ohms = Hill incline
Watts = VXA = Horsepower
Battery = Fuel tank
Alternator = Gas station

If you've ever looked a dyno trace there is a given horsepower for every point on the RPM torque curve.

In electrical circuits "rpm" would be fixed (12V, 24V, 110V etc.)

So a for a particular "hill" you need more or less amps to run the device. increasing amps is like stepping on the throttle harder pouring more gas from the fuel tank. when the tank gets low (about 50%) you need to turn on the gas station.

Resistance should be kept as little as possible so "dirty" circuits would be like driving up hill. RPM gets dragged down so horespower is less so the lights go dim or the blender turns slower or the blender heats up.

Each "device" is it's own little hill. A 12v LED is a pretty small hill. A 20a hair drier (on a boat) is like Pike's Peak.

If you continuously drive up Pike's Peak with the gas station on and the gas station can't pump into the tank fast enough eventually the lights go out.
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Old 20-04-2010, 20:52   #6
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If you've ever been electricuted you'll know the feeling of a wave of energy that paralyzes your muscles and "flows" through you.
Actually, if you've ever been electrocuted, you are now dead, and cannot read this!
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Old 20-04-2010, 23:36   #7
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to make electrical systems less confusing, is there a way to compare watts, amps, volts, ohms to, say, a car's; horsepower, speed, fuel burn, fuel capacity , etc ? I know usually a river is used as a simile. thanks.
I use a Spark Tester.

I grab the 2 wires and touch them together. The bigger the spark the more watts, amps, and volts I have.

Better done at night and with the engine on.

Wifey said if I did it one more time I would be ohmless



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Old 21-04-2010, 00:07   #8
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Voltage (V) is a measurement of electromagnetic potential. A huge voltage means there is a lot of potential for something to happen; picture a very tall waterfall. A small voltage means there is not a lot of potential; a very short waterfall.

Current (I) (Amperes) is the rate of flow of electrons. Think about your same tall and short waterfalls. High amperage means a high-volume waterfall, low amperage means a trickle. Notice that this is independent of the voltage.

Watts are like horsepower, the units both mean the same thing. A watt is a power unit. A high wattage circuit is like a tall, wide waterfall, it moves a lot of water a large distance, fast. Low wattage is like a small waterfall, moving just a little water.

Ohms are a measurement of resistance (R) . V=IR
A low resistance circuit through a 12 volt battery will draw a lot of amps. This is why shorts kill the battery. A high resistance circuit through a 12 volt battery will draw only a few amps.

This is somewhat counterintuitive. The lower your resistance is, the sooner your battery goes dead.

Okay fine I will use the car analogy

Watts are proportional to horsepower. Fuel capacity is proportional to joules of energy, or amp hours in a battery bank.

The speed of your car is somewhat proportional to the rate at which you burn fuel but the relationships are somewhat more complicated than DC electronics.
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Old 21-04-2010, 03:45   #9
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Volts get "pushed" at devices, but devices only draw the current they need. So if you stick something into a 12V supply it is going to get 12V. If that device only needs to use 0.5A then it will draw 0.5A current from the supply.
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Old 21-04-2010, 03:48   #10
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This is somewhat counterintuitive. The lower your resistance is, the sooner your battery goes dead.
The water analogy might be better. If you leave a tap fully open there is no resistance to the water flowing through it and your tank (=battery) will soon be empty. If you just crack open the tap, resistance to water flow is high but it will take ages to empty the tank.
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Old 21-04-2010, 06:40   #11
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Actually, if you've ever been electrocuted, you are now dead, and cannot read this!
How shocking!!
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Old 21-04-2010, 07:14   #12
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Iíve never been enamoured of necessarily imprecise analogies for mathematically exact electrical relationships.

See (specifically post #1)
"Ohm's Law & Boats"
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Old 21-04-2010, 07:24   #13
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That is an easy one:

Let me google that for you
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Old 21-04-2010, 08:05   #14
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I’ve never been enamoured of necessarily imprecise analogies for mathematically exact electrical relationships.

I'm with Gord on this one.
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Old 21-04-2010, 08:58   #15
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A pressure gauge is teed into the pipeline. There is no flow through it. It measures the difference in pressure from inside the pipe relative to the atmosphere.

A voltmeter has a high resistance, so essentially no flow through it, so it is equivalent to being teed into the wire. It measures the difference in potential between where the two leads are placed. If the black lead is placed at ground, that is like the atmosphere side of the gauge.

A flowmeter is placed inline on a pipe to measure gallons per hour. It is designed to impede the flow of water as little as possible.

An ammeter is placed in series in a wire to measure electrons per second. It has as close to zero resistance as possible.

I use a water tower to describe pressure/voltage. The higher the tower the higher the pressure. Nothing is moving, pressure is the potential to do work. The size of the water tower is the amphour capacity of the battery. The size of the pipe is the resistance. Carbon zinc batteries had a pretty small pipe.

For AC a capacitor is a rubber diaphragm in a chmber that allows no flow through other than when it is stretching. (OK for an electrolytic poke a pinhole or two in it.)
An inductor is paddlewheel connected to a flywheel.

John
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