Electric costs: 220 vs 3 phase with converter

[Clarence Martinn]

Seeing a lot of tools made these days with 3 phase motors with added converters to run on standard 220 Volts. What is the advantage of a 3 phase motor with a converter, vs a standard 220 Motor ?

[Mike Henderson]

I assume speed control. If that "converter" is a VFD it will use a certain amount of power which would add to your electric costs. Probably not enough that you would notice on your electric bill.

One advantage of a three phase motor is greater reliability compared to a single phase motor. The three phase motor doesn't have a starting capacitor or a centrifugal switch, both of which are common maintenance issues.

Mike

[Frank Pratt]

3 phase motors are cheaper to buy & last longer because of no start capacitor or switch. With a VFD the speed can be controlled & they can be programmed to soft start & braking on shutdown.

As far as efficiency goes, there is no reason why is necessarily more efficient than the other. That's down to the motor design. As Mike said, the VFD will introduce some losses, though not significant.

BTW, utility supply voltage for the single phase motor will be 120V or 240V. Three phase will be 208V, 480V, and in Canada, 600V as well. No such thing as 110V or 220V in Canada or USA.

[Bill Dufour]

Three phase motors almost never go bad except the bearings unless the cooling vents get plugged. With a VFD you get soft start, dynamic braking, instant reverse, variable speed, etc.
Bill D.

[Wes Grass]

Here in Calif we've got 240 3P. 2 120's, and a 220 'stinger'. But I've heard you can spec different on an install.

[Andy D Jones]

Three phase motors also have constant torque over the rotation of the armature.

Single phase motors' torque varies with the rotation of the armature. This causes "torque ripple" when running.

Thus a three phase motor runs more smoothly, with less vibration. That could translate into longer bearing and drive-train life (or same life from cheaper components), but may not be observable in many applications. It can provide improved surface quality in some metal machining operations.

-- Andy - Arlington TX

[Frank Pratt]

Three phase motors almost never go bad except the bearings unless the cooling vents get plugged.

That's just not true. Particularly when a motor is sized to work at or close to capacity. We regularly service machinery with burned out 3 phase motors. Not a rare thing at all.

[Mike Kees]

Clarence I run a rotary phase converter at my shop to power three phase machines. My converter will start up to a 10 h.p. three phase motor and run up to 30 h.p. of machines at the same time.My power bill has gone up at my shop mostly because I work there way more than I used to.

[Matt Day]

Seeing a lot of tools made these days with 3 phase motors with added converters to run on standard 220 Volts. What is the advantage of a 3 phase motor with a converter, vs a standard 220 Motor ?

And what hobby level machines (mostly what’s used on this site) are you seeing with 3 phase?

3 phase was and is the industry standard, for industry. It’s not new.

I’ve got 6 or so VFD’s on old machinery.

[Rollie Meyers]

Here in Calif we've got 240 3P. 2 120's, and a 220 'stinger'. But I've heard you can spec different on an install.

No 220V in California, but the high leg is 208V for 240V 3Ø. PG&E loves 120/240V Delta for AG services.