1 phase vs. 3 phase motor choice

M

mark thomas

Titanium

Joined

Dec 15, 2004

Location

SF Bay Area

• Dec 26, 2008

• #1

I have 3-phase power (via a Phase Perfect), and now I am wondering about new motors/tools that I can get in either single or 3-phase. For example, I need to replace a motor on a saw, and I can get a 1-phase or a 3-phase motor. Is there any reason to go with single-phase, other than things like ease of reselling, or should I just use 3-phase for everything now that I have the capability?

 

Forrest Addy

Diamond

Joined

Dec 20, 2000

Location

Bremerton WA USA

• Dec 26, 2008

• #2

No reason to change unless something happend to the single phase motor. Even then if you change out you have to change whatever electrical switching ran it. Can mean some bucks. No good deed (or idea) goes unpunished.

 

9100

Diamond

Joined

Nov 1, 2004

Location

Webster Groves, MO

• Dec 26, 2008

• #3

It probably doesn't make much difference on a saw, but I have sworn an oath to never run a single phase lathe again. In an emergency, sometimes you slap the switch and go over to reverse unintentionally. On a three phase machine, the motor reverses and starts to unroll you, as well as giving you time to get the switch back to neutral as it decelerates and starts up the other way. If a single phase motor is running fast enough to be off the starting winding, it just keeps going forward, compounding the damage.

Bill

 

B

Billiam

Aluminum

Joined

Dec 15, 2008

Location

Orange, CA

• Dec 27, 2008

• #4

Less vibration with 3 phase.

Fast reversing is good too, especially on a manual mill.

 

gwilson

Diamond

Joined

Oct 1, 2006

Location

williamsburg va

• Dec 27, 2008

• #5

Definitely use 3 phase on any machine like a lathe or other machine that you want to generate the smoothest possible finish with. Makes a big difference.

 

Bobw

Diamond

Joined

Feb 8, 2005

Location

Hatch, NM Chile capital of the WORLD

• Dec 27, 2008

• #6

I'd stick with single phase on the saw. In this shop we are still running phase converters, and at night we might be out back drinking a few beers and keeping the saw going(single phase) after all the machines are shut down. It would be a pain to keep a phase converter going for just that(that fricken' noise), or if you need a quick bracket or even a paint stirring stick cut off, or making some welded stupid thing, like a tractor or wind chimes, machines are shut down, phase converters off, the saw is going(and the welders).

 

The real Leigh

Diamond

Joined

Nov 23, 2005

Location

Maryland

• Dec 27, 2008

• #7

The comments regarding vibration and surface finish all relate to a fundamental characteristic of single-phase power.

The voltage at the load (the motor) goes to zero 120 times every second. So the motor exhibits a constant cycle of acceleration and deceleration. The inertia of the system minimizes this effect, but cannot eliminate it completely.

In a three-phase system, there is always non-zero voltage present on at least two of the three wire pairs. Although the magnitude of this voltage does vary with time, the fact that it never goes to zero greatly reduces the cyclic changes in motor power.

- Leigh

 

Spencer in NH

Stainless

Joined

Jan 22, 2007

Location

Southern New Hampshire

• Dec 27, 2008

• #8

I have been thinking along the same lines, in that I want to replace the single phase motor in my JET 13x40 with a three phase motor on a VFD. Anyone ever do that?

 

P

Pierce Butler

Hot Rolled

Joined

Jun 28, 2007

Location

Texas

• Dec 27, 2008

• #9

Spencer in NH said:

I have been thinking along the same lines, in that I want to replace the single phase motor in my JET 13x40 with a three phase motor on a VFD. Anyone ever do that?

Click to expand...

I replaced the 1ph motor on my 12x36 Grizzly with a 3 ph motor and VFD. I couldn't stand the 1 ph motor for several reasons.

1 - no instant reverse - try doing an instant reverse on a single phase. It just keeps on going forward.

2 - 1 ph motor noisy

3 - Locked to the gearbox speeds. Metric threading without a VFD is a real PITA.

 

Spencer in NH

Stainless

Joined

Jan 22, 2007

Location

Southern New Hampshire

• Dec 27, 2008

• #10

Pierce Butler said:

I replaced the 1ph motor on my 12x36 Grizzly with a 3 ph motor and VFD. I couldn't stand the 1 ph motor for several reasons.

1 - no instant reverse - try doing an instant reverse on a single phase. It just keeps on going forward.

2 - 1 ph motor noisy

3 - Locked to the gearbox speeds. Metric threading without a VFD is a real PITA.

Click to expand...

How does the VFD allow metric threading? The feed speed is a function of the spindle speed via the gearing. You can hand crank it, and still make threads.

???

 

9100

Diamond

Joined

Nov 1, 2004

Location

Webster Groves, MO

• Dec 27, 2008

• #11

After reading Billiam's comment about reversing a manual mill, I realized that I have been doing it for so long that I never even think about it. Especially on through holes where I can use a spiral point tap that pushes the chip out in front, I run the tap in on forward, then hit reverse when it has gone far enough. Trying this with a single phase spindle motor just means a scrapped part and broken tap.

I went for 9 years running a mill on a static phase converter in my basement, then for a couple more with a RotoPhase converter when I got my shop. I have no experience with a Phase Perfect, so I can't comment there, but neither of the converters I used came close to the performance of the three phase line I finally lobbied Union Electric into installing.

Bill