Single, 2 or 3 phase -- what's it mean?

[sheslostcontrol]

I'm looking at air compressors and keep seeing references to "3 phase" or "single phase" in the listings.

What is phase and how does it affect performance, reliability and usability?

 

[Mike83]

I'm not an expert, so folks please correct me, but generally most people do not have access to 3 phase which is 480volt power. 3 phase makes motor brushes unneccesary because it provides a more continuous source of power. This in turn will eliminate that wear item and increase reliability. Generally household power is single phase 110 or 220V.

Again, just my unprofessional take on it.

 

[jwx]

I'm not an expert, so folks please correct me, but generally most people do not have access to 3 phase which is 480volt power. 3 phase makes motor brushes unneccesary because it provides a more continuous source of power. This in turn will eliminate that wear item and increase reliability. Generally household power is single phase 110 or 220V.

Again, just my unprofessional take on it.

Pretty much a easy way of putting it. This wiki page looks like it has a better, more technical explanation on it, http://en.wikipedia.org/wiki/Three-phase_electric_power

 

[mtwaterguy]

The lighting and electrical forum would probably get you more responses.Good luck.

 

[rsanter]

3 phase is when you have 3 individual electric 'legs' or sign waves. these are operating 120 degrees apart from one another.
think of the 'legs' as the pedals on a bycycle. 3 phase would have 3 pedals spaced equally apart. 3 phase is more efficient and will make the same HP in a smaller package because there is always one pedal or 'leg' in a position to be pushing down.

I have always thought that 220 should be called 2 phase because you have 2 'legs' located 180 degrees apart. just like a bycycle you will have a short period where the momentium of the motor will carry it or coast over the top and then the phases will push the pedals again

single phase is a single sign wave and is just like a bycycle with only one pedal

for residential with a compressor, go 220v if you can
if you go with 3 phase you will need a converter. this can work fine if you get a good enough deal on the compressor

bob

 

[Nealcrenshaw]

Yeah, What Bob said!!

 

[Rigmaster]

Not a technical or in-depth description, but I once heard it explained like this:


Imagine needing to drive a train track spike into a railroad tie.

Single phase is like 1 guy swinging a sledgehammer hitting the spike- he hits it, then rests a bit, then hits it again.

3 Phase is like 3 guys of similar size/strength as the single phase guy- but they're standing in a circle around the spike, first one hitting it, then the next guy, and so on.



Not sure if this is a great example, but it helped me with my admittedly VERY limited understanding of 3ph vs 1ph.



One thing to consider if you buy any 3phase equipment for your home and you do not have access to 3ph power- you will need a converter to make the equipment work on your single phase power. The good ones can be VERY expensive. There are some DIY solutions, but you really have to know what you're doing to make them work- and even then they can cost $$$ if you have to buy the parts to make a converter.

 

[Zrexxer]

Simplest answer: If you have to ask, you don't have three phase power.

 

[84scrambler]

Look at this link as well. This is the way residential power is run in the United States.

http://en.wikipedia.org/wiki/Split_phase

 

[Dan0myte]

Here's my crappy MS Paint visual of what the previous posters are talking about.

Your +Vpeak and -Vpeak remain much more consistent with 3 phase than when you have single phase power. The power efficiency results in electric motors that can be more powerful, more efficient and cheaper to produce than single phase motors.

 

[Mickey O]

3 phase is when you have 3 individual electric 'legs' or sign waves. these are operating 120 degrees apart from one another.
think of the 'legs' as the pedals on a bycycle. 3 phase would have 3 pedals spaced equally apart. 3 phase is more efficient and will make the same HP in a smaller package because there is always one pedal or 'leg' in a position to be pushing down.

I have always thought that 220 should be called 2 phase because you have 2 'legs' located 180 degrees apart. just like a bycycle you will have a short period where the momentium of the motor will carry it or coast over the top and then the phases will push the pedals again

single phase is a single sign wave and is just like a bycycle with only one pedal

for residential with a compressor, go 220v if you can
if you go with 3 phase you will need a converter. this can work fine if you get a good enough deal on the compressor

bob

They are not not 180 degrees out of phase, they are polar opposite on the same phase.

 

[Nealcrenshaw]

They are not not 180 degrees out of phase, they are polar opposite on the same phase.

HUH?? They're 120 degrees apart.

 

[woody 73]

Hi Ringmaster got it right...I have asked several electricians over the years to help me with 3-phase and they all talked me out of it... I have passed up many great machines due to three phase motors. Stick with single phase because most people will buy it. On the other hand you will get fewer taker's when you try and sell your three phase machines.

I have been told that because three phase motors have fewer moving parts they tend to last longer , well that's what people tell me.

 

[Mickey O]

HUH?? They're 120 degrees apart.

No they are not, single phase 220~240 is two 110~120 volt legs in the same phase, polar opposites.

Take a look at the three phase sine wave below, along 0, there you can see the phase shift.

 

[bosskong]

They are not not 180 degrees out of phase, they are polar opposite on the same phase.

Isn't that like saying "it's not 50%, it's half"? i.e. aren't they the same thing?

 

[Mickey O]

Isn't that like saying "it's not 50%, it's half"? i.e. aren't they the same thing?

Not even close, take a good look at the two sine waves, we're talking about two completely different things. And there's a whole lot more to it, delta, WYE, 208, 277, 240, 480, etc.

I think the original poster is just wondering if he should buy 3 phase equipment, if it's 480, no, if it's 240 and he wants to invest in a phase converter you can get some real good deals on great equipment. But compressors with real large motors may draw too much current for most home services.

 

[lametec]

Take a look at http://en.wikipedia.org/wiki/Phase_(waves). It might help explain it.

 

[WVU Tuba Dale]

Not to be picky, just wanted to add a little to the conversation, but it is a sine wave, not a sign wave. No hard feelings.

 

[Mickey O]

Not to be picky, just wanted to add a little to the conversation, but it is a sine wave, not a sign wave. No hard feelings.

What if you paint the sine wave on a sign? Then it would be a sign wave. The real question is if you eat fried chicken in Kentucky is it Kentucky fried chicken?

 

[WVU Tuba Dale]

Only if the fryer is a "Kentucky" brand, and it is made in the USA.

 

[rsanter]

They are not not 180 degrees out of phase, they are polar opposite on the same phase.

I understand what you are saying
I was simplifing it for understanding
although if you look at it and shift one wave by 180 or half a cycle, you will have them on the same path

bob

 

[sheslostcontrol]

Ok so I need to look at a 2-phase 220v compressor. What's the best I can buy for $1500? I would want to sandblast, paint, use air wrenches, ect. I strongly prefer buying something manufactured and assembled in America even if I get a little less compressor vs. Chinese harbor freight imports. Thanks.

 

[930dreamer]

For a garage a single phase 240V air compressor would be best. I built a Rotary phase converter for almost free and run a IR compressor with two 3hp 3phase motors. This is in the crude phase.