VOLTAGE IS PRESSURE?
Then how many ATM equals One Volt?
2004 W. Beaty
If voltage is like pressure, what pressure is it?
Let's make a bunch of assumptions. Looking around on various pages of
hydraulic backhoe pumps, I find that a
30 cubic in/sec flow rate pump can run at 1500 psi, transferring about 5
kilowatts. What are the typical hose diameters like? Maybe 1" inside?
So, if a 5KW DC motor runs at 240v and 20 amps, and if the wires are
equal in size to the hydraulic hoses above, then what hydraulic pressure
"equals" one volt of potential?
The speed of the "electron fluid" is slow, but the speed of the hydraulic
fluid in the hoses is fast. Pressure will have an inverse change (since
watts is proportional to fluid speed times pressure diff.: we must raise
while slowing the flow, so that power remains constant.) The speed of
fluid in the above example is about 30 in/sec. Using
/miscon/speed.html, the speed of charge carriers for 20
amps in 2cm solid copper "hoses" is around .0002"/sec.
Therefore, if a hydraulic system was flowing at .0002" per second
rather than 30" per second, yet was still delivering 5 kilowatts, the
pressure would have to be proportionally higher than 1500 psi.
I make it out to be...
Very rough calculations, lots of weird assumptions, might be off by 2x or
- 1 volt potential "equals" a hydraulic pressure of 1,000,000 psi
Huh. So that's why electrons can flow so slowly in everyday circuitry.
The "workng pressures" in simple electric circuits are
astronomical when compared to the hoses in industrial hydraulics. And the
resistance of wires is
terrible, it's huge: like pumping hydraulic fluid through packed sand or
Even worse than that! Electric circuits are like
pumping warm tar through pipes full of packed sand. If it moves fast
enough for humans
to notice the motion, it would char itself from the frictional heating.
Circuitry has high pressure, slow flow, and not much heating caused by
fluid-flow in the mile-long tubes of sand, tubes called "the power grid."
And think about AC power systems. It's not just one volt anymore.
Sending megawatts down an AC line is like sending 60Hz sound waves along a
long column of fluid, with the sound pressure being hundreds of billions
of PSI, and the fluid inside the pipes only vibrating microscopically back
Now if only hydraulics behaved like wires! In that case a hydraulic
motor could still turn at a decent speed, even when supplied with extreme
mega-PSI pressure and almost no flow rate. The oil could move at 1mm per
hour, while the oil-motor spun at 1000RPM. With a setup like that, the
losses in miles-long hoses would be tiny, and we could replace all of our
power technology with "hydr-icity pipes" instead of "electr-icity" pipes!
Separate topic. In some pop science book (perhaps "Time Travel and Papa
Joe's Pipe," the author mentioned a question asked by his aging father.
The father had had lots of experience in heavy machinery, and knew just
how many maximum watts of mechanical power could be sent down how large a
particular driveshaft. But the father was always confused about
How could megawatts be sent down a half-inch aluminum cable by an
electrical generator? Why are wires so small when compared to the
equivalent steel drive shaft?
The above hydraulic analogy supplies the answer: "pressures" in
electrical circuits are stunningly huge! One volt equals a million pounds
per square inch! The "electrical pipes" don't burst until you reach much
higher pressure than that; the analogous giga-torr levels. And even the
simplest tiny "electricity pump" can easily produce such "pressures."
With such things attainable, huge wattage can be sent down a long "hose"
where the fluid in the "hose" need only crawl along imperceptibly, and the
"hose" can be extremely narrow, yet deliever relatively huge energy-flow.
Yet at the same time, wires have enormous frictional problems, and if the
"electron fluid" should ever be pumped at a speed humans can see (say a
few cm per second,) the wire quickly heats up and melts!
As a hydraulic system, electric circuitry is very strange: it uses the
analog of gigantic pressure, yet at the same time it's not practical to
pump the "fluid" in the pipes any faster than a snail's pace.