Converting 3ph to 1ph

[Mike Cruz]

Is converting an old/older 3 phase machine to single phase as simple as replacing the 3 phase motor with a single phase one? Okay, and maybe a new switch? Or does that throw off any other electronics in the machine? I'm looking at an older lathe and I don't believe that it has a digital readout or anything like that. Thanks for your input.

[keith jensen]

Mike,
The guys at OWWM have a section dedicated to 3ph power. There are a number of ways to get from single phase to 3ph. They cover it really well.
1. Variable Frequency Drive or VFD for lower horsepower motors (3hp and under) are relatively inexpensive plus you get variable speed control and braking (with the right hardware).
2. Rotary phase converter, a second 3 phase motor with a motor starter to get it going. So you have an idler motor generating the 3rd leg of the 3ph.
3. Static converter, runs motors at 2/3 of the horsepower rating. Harder on motors though.
4. Single phase motor replacement requires a new magnetic starter (generally) as well.

I run a VFD on my PM66. Super easy, even kept the same start/stop which was rewired of course to take out the mag switch.

I know I'm forgetting one of the options....check out OWWM though.
Keith

[Darnell Hagen]

A 3 phase lathe is an ideal candidate for a VFD, converting from single phase and giving you electronically controlled variable speed, slow start, and motor braking. Unless it's 550v, then you're gonna need a transformer.

[Jonathan Spool]

You don't need to change out the motor if you get a static converter. All depends on thye HP and whether you will need to purchase the replacement motor, I guess. A Static converter for 1-3hp will run around $125

[Mike Cruz]

So, with prices being approximately 1 hp- $150 2 hp- $225 3 hp- $300, it seems as though if the lathe has under a 3 hp motor, it would be smart to put a VFD or Static converter on it.

If it has a larger motor, say 5 hp, then it might be another story...

Thanks for the info.

Oh, Keith, you mention that a new motor means a new magnetic starter. Sorry for my ignorance, but what starter?

[Logan William]

A magnetic starter is how it should be wired so that if it loses power while on(breaker, power surge etc) it will "disconnect" power due to losing the magnetic field that was generated by the current flow so when power is regained(power company fixes their end, you flip breaker) the device won't suddenly power back up.

If it was me I'd put a VFD on it. I'm going to be doing that very thing this winter on a Yates-American disc/drum sander I actually bought off the OWWM classifieds. Check out FactorMation.com, under the AC Drives section they have their line of VFD's that should fit your application, the FM50 should handle what you need.

[Stephen Cherry]

Like everything, it all depends on the details.

VFD is the easy choice, if you don't have variable speed on the lathe already, it would be a big plus. You need to be a little careful though because as the speed of a motor is reduced, the fan, if equipped, does not work as well. Also, a mechanical variable speed, such as the variable diameter pulleys, or multiple pulleys, gives a torque rise as speed is reduced. A VFD, at best, would maintain the same torque.

If the lathe has a mechanical variable speed, and a healthy motor, the static phase converter would be OK also, but you loose about a third of the motors power. You also need to make sure that the thermal overload on the motor is set to match the motors nameplate current rating, so that it is not fried. Basically, all the static phase converter does is add a capacitor from one of the two supplied legs, to the third leg of the motor, while the motor is starting. The catch is that it needs to be unhooked before it blows up. This could be actuated from another contact on the start switch.

[Bill LaPointe]

I used a RFD on my 2 hp metal lathe. Based on this forum info, I think if I had it to do over, I would go with the VFD.

[Mike Cruz]

So, by magnetic starter, you mean a magnetic switch? Oh, I knew what that was, I thought ya'll were talking about another piece between the switch and the motor or something. Got it, thanks.

[Logan William]

So, by magnetic starter, you mean a magnetic switch? Oh, I knew what that was, I thought ya'll were talking about another piece between the switch and the motor or something. Got it, thanks.

All depends on what you have for a switch, sometimes they put the magic green and red buttons on the front side of the case of the mag starter(more common on older starters), on others its a seperate enclosure due to its size.