I need an air compressor for small dive operation.

[Wookie]

For us in the "outside the US " world, it is 220V single phase or 380V 3-Phase (50 Hz). Is 220V/50Hz 1-Phase has the same issue as the 110V 1-phase?

No. Amps are what do work. Power = volts times amps times the power factor in a single phase system and volts times amps times the power factor times the square root of 3 in a 3 phase system. Assume that there is no way for you to affect the power factor. So just going from three phase to single phase lowers available hp by the reciprocal of the square root of 3. Going from 220v to 110v doubles your amps, or halves your power. If your amps double, your conductors have to be oversized to dissipate the heat from losses. It’s a losing battle.

 

[BRT]

No. Amps are what do work. Power = volts times amps times the power factor in a single phase system and volts times amps times the power factor times the square root of 3 in a 3 phase system. Assume that there is no way for you to affect the power factor. So just going from three phase to single phase lowers available hp by the reciprocal of the square root of 3. Going from 220v to 110v doubles your amps, or halves your power. If your amps double, your conductors have to be oversized to dissipate the heat from losses. It’s a losing battle.

Sorry Wookie. Power is what does work. Your math is correct. Zero amps times 1000 volts is zero work and zero volts times 1000 amps is zero work. This is why the power factor is in the equation. Going from three phase to single phase raises the amperage for the same horsepower by the square root of 3, 1.73 times. Three phase is much better for the same horsepower for wire size, starter size and motor complexity. Three phase motors have no internal start switches and no capacitors to make them start and/or run unless the capacitors are added to the system to improve power factor.

 

[Wookie]

Sorry Wookie. Power is what does work. Your math is correct. Zero amps times 1000 volts is zero work and zero volts times 1000 amps is zero work. This is why the power factor is in the equation. Going from three phase to single phase raises the amperage for the same horsepower by the square root of 3, 1.73 times. Three phase is much better for the same horsepower for wire size, starter size and motor complexity. Three phase motors have no internal start switches and no capacitors to make them start and/or run unless the capacitors are added to the system to improve power factor.

I'm trying to give the guy an understanding, not necessarily be technically correct. I'm more than happy to discuss impedance and inductive capacitance and I^2R losses and be technically correct, but for the purposes of "Why is 110 volts less desirable in a motor than 220 volts", the answer is that you can't shove enough electrons through a standard motor to get the work done.

Don't get all Navy Nuke on me.

 

[Billy Northrup]

I wouldn't be going out on a limb saying 3p is at least 10% more efficient (example 240 split phase vs 208 3p), even better at 480v. This difference can put some more money in your pocket on a slim margin product.

It's why I like regulators and allot of whips, I have better things to do with my time than tending tanks.

 

[BRT]

I wouldn't be going out on a limb saying 3p is at least 10% more efficient (example 240 split phase vs 208 3p), even better at 480v. This difference can put some more money in your pocket on a slim margin product.

It's why I like regulators and allot of whips, I have better things to do with my time than tending tanks.

I would like to see any actual data showing that three phase motors are more efficient (use less electricity to make the same amount of power)

 

[Wookie]

Navy says 3 phase motors are preferable because they are smaller, lighter, cheaper, easier to maintain, won't rust, bust, or collect dust. But power is power. I can't imagine that they use any less electricity over single phase. They just use it differently.

 

[BRT]

Navy says 3 phase motors are preferable because they are smaller, lighter, cheaper, easier to maintain, won't rust, bust, or collect dust. But power is power. I can't imagine that they use any less electricity over single phase. They just use it differently.

Three phase is way superior. I never want to own a shop without it. I've always wondered if three phase motors were actually more efficient but never had good information or a good way to make a test. I have a recording wattmeter but there are so many variables in loading that it would be hard to make sure a test was accurate.

 

[Wookie]

Three phase is way superior. I never want to own a shop without it. I've always wondered if three phase motors were actually more efficient but never had good information or a good way to make a test. I have a recording wattmeter but there are so many variables in loading that it would be hard to make sure a test was accurate.

As you said earlier and were correct, power is power. If it takes 10 Hp to run a compressor, it doesn't matter how you make the 10 Hp, it takes the same amount of power. Comparing electricity to say the power of a horse, electricity is far more efficient. Comparing electricity to electricity results in the same outcome (or input).

But for all of the reasons we have both stated, 3 phase motors are better because they are indeed smaller, lighter, easier to maintain because they use smaller lighter windings and no start capacitor. You might make an argument that a 3 phase motor is more efficient than a single phase if inrush current were factored in, but then you'd be starting and stopping every minute or so for it to be enough to make a difference, and if you were doing that, you'd use DC.

 

[BRT]

As you said earlier and were correct, power is power. If it takes 10 Hp to run a compressor, it doesn't matter how you make the 10 Hp, it takes the same amount of power. Comparing electricity to say the power of a horse, electricity is far more efficient. Comparing electricity to electricity results in the same outcome (or input).

But for all of the reasons we have both stated, 3 phase motors are better because they are indeed smaller, lighter, easier to maintain because they use smaller lighter windings and no start capacitor. You might make an argument that a 3 phase motor is more efficient than a single phase if inrush current were factored in, but then you'd be starting and stopping every minute or so for it to be enough to make a difference, and if you were doing that, you'd use DC.

I have successfully used variable speed drives on 3 phase motors for cycle times much shorter than every minute. You have to size the motors up.

 

[Wookie]

I have successfully used variable speed drives on 3 phase motors for cycle times much shorter than every minute. You have to size the motors up.

You certainly can do that, but for motors that stop/start frequently, a power source other than AC is preferred.