Help me really understand volts and watts...

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Mbira

Well-known member
Joined
Jun 4, 2004
Messages
2,422
Location
Austin, TX
So I have been trying to get more into wrapping my head around what's really happening in these circuits. Please forgive my extreme ignorance with the foundations of the things we all love here. Reading the Art of Electronics over and over, I finally think I really understand amps. One amp equals the movement of a certain number of electrons from a negative place to a positive place in one second as measured at one point in the circuit. I forgot the number of electrons now-I don't have the book in front of me. So amps is easy for me to visualise. Watts on the other hand is hard for me to grasp. OK, it's the amount of power (in joules) to make electrons move from point a to point b, but what the heck is the power? Does that question even make sense? Is the powr based on voltage differences between point a and b? So the bigger voltage difference would make things go faster? Wait, that's watts, right? AHH! Sometimes I feel like a 4 year old in here...

Joel
 
The water analogy:

Volts = depth of the water
Amps = the rate at which the water flows
Resistance = opposition to flow
Watts = the amount of water consumed
 
hmm I'm with you on the water analogy up until the point of wattage.

energy is not consumed, but rather changed into another form. in electronics, the electron(or hole if you are one of *those* types) flow is impeded by resistance and therefor gives off excess energy as heat. this heat is what we usually consider as wattage, but remember that wattage is just a measurement tool. and forgive the layman's explaination please.

in the human body excess energy is given off as heat too, we call it a calorie.

water flows from high concentration to low concentration just like electrons do. they are both impeded by things in their way.

and another analogy that fits..

too much flow and your pipes can burst!
 
watt=current X volts and it's the total work available from the two factors.

think of two horses, on can carry 100kg and run 10kmph, the other can carry 50kg but runs 20kmph, the total work they do is the same.
 
I've always thought of it like an air compressor & a framing gun.

Current=volume of air moving through the hose
Voltage=pressure at which the volume of air is being moved.
Watts=The amount of power (ie: The product of air volume & pressure) available to the gun on the other end to work.

lower the air volume (ie: use a 1/4" hose vs a 3/8" hose), there's less power available to the gun. Lower the pressure & don't mess with the volume, there's less power available to the gun. Raise either or both & there's more power to the gun.

Impedance= the gun's trigger. Valve closed= high impedance. Pressure remains steady, airflow stopped=no work. Valve open=pressure remains steady (theoretically), airflow increases=work. Low impedance hose drives a high impedance air gun...

And hopefully throughout it all, you didn't nail your boot to your foot :green:

:thumb:

Todd
 
V(Volts) is a potential
potentially something can happen

If there is an available path and a load, then a I(Current) can flow
the amount of current is inversely proportional to the R(Resistance) of the total load

V=IR

When you have both Volts and Current there is a change is energy level of something.
That energy used is measured in W(Watts) and this is directly proportional to the total work done

W(Watts) = V(Volts) X I(Current)


The water analogy ...
the high above the work is the potential of the water to do some work
top of the mountain is a lake
size of the pipe has a bearing on the amount and speed at which the water can flow
this can influence the amount of work that can be done at the bottom of the mountain ... when turning the turbine to create an energy change.

use much energy and the speed of the water is reduced ... don't use the energy and it remains in the water ... Still at speed ... until something does something does use that energy.

all things find a way to get to a lower energy level.
:roll:

never did like water analogies ... try to think electricity.
Potential
Paths
Loads
then comes the distinction of DC and AC circuits
 
V(Volts) is a potential
potentially something can happen

So my question is potentially WHAT can happen? On the electron level, what are we saying is happening? More volts means that more electrons can move from point a to b in the same amount of time? Wouldn't that just mean more amps? What is happening on the electron level (theoretically I know) with volts?

Thanks.
Joel
 
[quote author="Butterylicious"]The water analogy:

Volts = depth of the water
Amps = the rate at which the water flows
Resistance = opposition to flow
Watts = the amount of water consumed[/quote]

This is basically how I consider all electronics.

Components become analagous too - resistors are taps, capacitors are buckets, etc.

I have a slightly different way of looking at it where the voltage is the pressure of the water, but it all works out the same for me.
 
are so you want some quantum theory stuff ?

mmm ... this one can spark (get it ?) lots of different analogies and therories

yes most would agree that more electrons leads to more current
then comes the srgument that electrons don't flow at all

Pontential for a change in Charge.
we started with Volts ... not Charge.

errr Coulomb's Law perhaps ...

this get very theoretical and largley doesn't help with DC and AC circuits
I'm probably not the right person for this one as I'll just want to head for string therory and then I'll confuse myself
This stuff is more fascinating than it is helpful for audio ... :roll:

are you sure you want to do this ... It probably won't help in the long run when looking at an EQ or a power supply ... perhaps for a Condenser Microphone.
 
Hmm...OK, so having read that coulombs law link...
So volts being 'potential' means that if you had some circuit and it was 9 volts at 100mA and it dissipated x amount of energy (watts) then if you just turned it up to 18 volts, would the amps go down?
 
No, in most circuits the current would increase. Consider a very simple circuit, a battery connected across a resistor. Compute the current in the resistor. Now double the battery voltage: what happens to the current?

The "pressure" analogy is a useful way to look at voltage. When the pressure in a water tank is too high, the tank can burst... and when voltage is high enough, it can "burst" (arc) across dielectrics--such as air--that were adequate to contain it at lower pressure.

At the electron level, voltage is simply another way of saying "charge", the amount of electrons present relative to a reference quantity.
 
In lamen's terms for electricians:
Consider a 20 amp branch circuit loaded at 75% (15 amps)
120x15=1800 watts, 277x15=4155 watts
Disregarding constant duty factors. a 3 lamp T 12 fluorescent light draws 120 watts
1800/120=15 lights per circuit, 4155/120=34.6 lights per circuit
There's your trade off right there. As voltage increases, current drops for the same amount of work. That's why in the US, they generate at 346KV nominal. could you imagine the size of the wire required to feed even a small town if generated at 120V? Wire should be sized in accordance with overcurrent protection. Over current protection should be size in accordance with load demand.

Even though pressure is a better description of voltage, I don't like to use it because people tend to think larger wire is required for larger voltages. Actually it's the insulation that needs to increase (enough insulation to contain the pressure). Wire size needs to increase with relationship to flow (current). Watts is the unit of consumption. It doesn't matter what the voltage is, a 40 watt lamp draws 40 watts.



I used T-12 wattage for simplicity of round numbers.
 
So amps is the number of electrons flowing across a specific point in the circuit.
Volts is the number of electrons sitting there on the negative rail of a battery waiting to get to the positive rail-the greater the voltage the greater number of electrons there are there.
Watts is the amount of electrons escaping when those electrons go on their trip(from resistance only?).

The trippy thing is that these three things are so related. If you had more electrons on the negative rail (Volts), then they would want to get to the positive rail therefore increasing the Amps.

Is that right?

:guinness:
 
> Volts is the number of electrons sitting there on the negative rail of a battery

No, Volts is how hard they "want" to move. Do they have a great urge to move, or are they apathetic about the idea of moving?

Volts has no meaning for a single point. Volts is always between TWO points. In the real world we often have some large sorta-conducting object around, such as a chassis or the dirt, so sometimes we simplify by making that large object one of the two points, and then forget to mention it.

Say you stand across the street from a bar with $4 Miller beer, and you are not very thirsty. You feel very little "voltage" pushing you across the street. Now say you stand across the street from a bankrupt studio, and the landlord is throwing vintage Neve modules in the trash. You feel a very large voltage urging you across the street.

> One amp equals the movement of a certain number of electrons from a negative place to a positive place in one second

Current could be seen that way, but it is usually best to draw a line across a conductor and count the electrons which cross the line. Same as the rubber hose across a highway used to get traffic-count. Main St carries 4,321 cars per hour. 1 Amp is one zillion electrons crossing the line in one second. The exact big-number is not used in practice.

Going back to the dumpstered Neves: if many geeks have easy access, there will be a large current of geeks moving toward that dumpster. If it is way out in Allice Springs behind a 10 foot wire fence with guard dogs, very few geeks will overcome the resistance in the way.

> Watts on the other hand is hard for me to grasp

The root definition is the work one horse can do. This concept comes from coal mines under the sea: to lift water out as fast as it came in, a mine might need 1, 2, 3 or however many horses working the pump, and Jimmy Watt sold engines on the basis of how many horses could be replaced. Watts are the same thing, except defined in terms of the arbitrary non-horse units Volts and Amp. A Watt is about a 1/750th of a Horse, or say a horse about 1 hand tall.

The gut-level definition of Watt always comes down to HEAT. A small car can cruise the highway with 10 horsepower or ~7,500 Watts. This power goes to move the air the car hits so it goes around the side of the car, mechanical energy. But power always ultimately appears as heat. At 60MPH, the air heat is small, but at 2,000MPH it melts metals.

Watts, Power, Horses, is always two factors. Lifting water out of a mine, you can lift 33,000 pounds one foot in one minute, or 1 pound 33,000 feet in one minute. Conversely, you could get 1 horsepower from a water-wheel if you had 1 pound per minute falling down a 33,000 foot pipe or 33,000 pounds a minute falling 1 foot over a low dam, or 330 poinds/min falling 100 feet. They are different wheel designs, but you can get the same work done.

In electricity, if you need 1,000 watts to warm a cold room, you could use 100 Amps from a 10V supply or 1 Amp from a 1,000V supply. You need different resistances, but you get the same power and the same heat. Likewise you could burn a big pile of damp wood, or a small pile of oxy-hydrogen: temperature times size is heating power.

> The trippy thing is that these three things are so related.

How big is your farm? It is so-wide times so-long and so many acres.

Perhaps a better analogy: how powerful is your farm? It is the area times the sun+rain that falls on it. Sun and rain are the "voltage" that makes plants grow: an acre in Siberia or Nevada won't grow as fast as an acre in Brazil or Florida. Even with big sun and rain, plants don't grow instantly: there is "resistance". But Volts divided by resistance gives a "current" like one foot of growth per week, or one acre-foot of produce going out your gate to market each week.
 
That just about brought tears to my eyes...

:thumb:


Thanks PRR. I'm gonna read that several more times just to let it sink in.
 
I don't know what to say
:shock:

I think I'd rather go back to the Lake at the top of the mountain analogy ...

FARMing !!
But Volts divided by resistance gives a "current" like one foot of growth per week, or one acre-foot of produce going out your gate to market each week.

so funny ... I love it

sorry
I want to do a whole bunch of NZ and sheep jokes now ...
:green:
The LAB realy is worth spending time at
:thumb:

So Joel,
it all makes complete sense now ?
 
So Joel,
it all makes complete sense now ?

Yes, as crystal clear as...err...well...yeah :green:

I'm still grocking it, man...

:guinness:

PS: the $4 Miller is what brought it all into play for me...
 
Remember that an electron sitting on one battery terminal waiting to get across to the other terminal will lose energy when it travels through the circuit . How much energy depends on how much voltage. An electron going from 12 volts to zero will only do half the work of an electron going from 24 volts to zero.

So watts is really just how many electrons and where are they sitting. If they sit high on the cliff, they make a bigger noise when they fall off and hit the ground.

A fixed amount of electrons falling from a fixed potential will produce a fixed wattage. Change either the number of electrons, or the height of the cliff they sit on, and you change the wattage.

Thus, volts (how high the cliff is) x amps (the number of electrons) = watts.

Good watts in our area of electronics is sound, bad watts is heat.
 

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