Base single to 3phase system

[JP McG]

Hello,

Just managed to score a SAG12 lathe in great condition for 1k and wanted to ask folks opinion on what you think the best system to run the 3 phase motor on is? I have 220V power run to the workshop. I believe the motor is a 3hp looking at details online from others that are for sale. I'm a tad (well totally) lost when it comes to Variable Phase Drive or Rotary/static converters. I've been reading up and it seems like there might be an issue running the coolant off VFD as it might fry the motor.

Does anyone have any recommendations on what makes sense to install to get her up and running, (I don't have other three phase tools so the cheapest system that works is what i'm after).

Thanks for your time!

JP

[John Hasler]

Get a VFC.

[SteveM]

Run the spindle motor off the vfd.

Separate anything else, e.g. coolant pump, and run them off something else, be it 1 phase or a static phase converter if the pump is 3-phase.

You don't want your coolant pump speed changing with the spindle speed.

Steve

[JP McG]

Thanks for the replies. I'm realizing I have to up the voltage to 440 from my 220 supply. Would something like the phase converter/transformer in the link below deal make the most sense? and avoid having to have two setups for the spindle and coolant motor?

https://www.wholesaleweldingsupplies.ie ... ct_id=4072

[SteveM]

Not being an expert in motors, despite sounding rational in my prior post, the only question I would have on that converter is that it outputs 415 volts and not 440.

This also appears to not be a VFD, so no speed control.

The VFD will vary the frequency of the output, so turning it down to 30Hz will run your lathe at half speed.

You could use a phase converter to give you the three phase without the speed control. You would then have the speed control that the lathe has. You would first need to get the voltage up with some form of transformer.

Steve

[Steggy]

Hello,

Just managed to score a SAG12 lathe in great condition for 1k and wanted to ask folks opinion on what you think the best system to run the 3 phase motor on is? I have 220V power run to the workshop. I believe the motor is a 3hp looking at details online from others that are for sale. I'm a tad (well totally) lost when it comes to Variable Phase Drive or Rotary/static converters. I've been reading up and it seems like there might be an issue running the coolant off VFD as it might fry the motor.

Does anyone have any recommendations on what makes sense to install to get her up and running, (I don't have other three phase tools so the cheapest system that works is what i'm after).

Thanks for your time!

JP

I'm not entirely clear on something. You mention a coolant pump. Is that pump a single-phase or three-phase device? Also, what is the operating voltage for the machine (208, 220, 440, etc.)?

As for powering the lathe itself, I'd recommend using a digital phase converter (also referred to as a static phase converter to distinguish it from a rotary converter) or a variable frequency drive. The former generates three-phase power using a double-conversion process that produces balanced output, which is essential for good motor performance. In general, the output frequency is 60 Hz, same as the power line frequency, which means the lathe's motor will run at the same speed it would if it were powered directly from a three-phase line.

A variable frequency drive (VFD) combines digital phase conversion with the ability to vary the output frequency. As the speed of an induction motor proportionally varies with frequency, having a VFD connected to your lathe will allow you to run it at wide range of speeds by merely twisting a knob or pushing a button. In the case of a lathe in which spindle speeds are changed by messing with V-belts, this is a very convenient feature.

Now for the caveats. Use of digital phase conversion in any form can give rise to several motor problems, especially with older machines. The conversion circuitry may generate high frequency electrical "hash" that older motors may not handle well, resulting in insulation breakdown and internal flashover, which will destroy the motor.

Using a VFD to run a motor at low speed may cause overheating, since most motors are fan-cooled and the output of the fan greatly diminishes at low RPM. Typically, this problem is dealt with by rigging up an auxiliary electric fan to supplement cooling air flow.

Most VFDs make it possible to run the motor faster than its rated RPM (nominally 1750 for a four pole motor on 60 Hz). In order to do so, the output frequency must be increased above nominal, and a corresponding increase in output voltage is required to maintain rated current flow under load (a goal of most VFDs is to maintain constant motor horsepower over a range of speeds). As the frequency increases, eddy currents in the rotor become more intense, leading to a dramatic rise in rotor temperature. The temperature rise, when combined with the mechanical effects of being overdriven, may cause the bus bars in the rotor to dislodge, ruining the motor—in some cases, such a failure may cause the motor to abruptly seize, possibly causing machine damage as well.

A special class of motors referred to as "inverter-rated" is designed to tolerate operation with a VFD. Typically, such motors have greater-than-normal cooling capacity, are wound to accommodate the wide frequency range at which they will be powered—especially when the voltage is increased to run above nominal speed, and have a reinforced rotor to tolerate being overdriven. Such motors will also have a speed range specification, usually expressed as a ratio, e.g., 10:1.

Before you invest in any phase conversion hardware you need to know if your lathe's motor can safely be operated at other than standard line voltage and frequency. If it can, then a VFD is practical. If not, fixed-frequency phase conversion is required. Incidentally, home-made rotary phase converters made from three-phase motors are not ideal by any means—most such arrangements suffering from phase imbalance and poor efficiency.

[SteveM]

Good information, dinosaur.

I learned something new today.

Problem is, every day, I forget two things.

Steve

[liveaboard]

On the other hand, I just slapped a modern VFD onto 2 antique 3-phase motors and they're working just fine.
If they die, I'll replace them.
I run from 30% to 200%.
I don't load the motor too much at low speed and high speed makes me a bit nervous.

[Bill Shields]

coolant motors on a VFC running at 100% speed are generally not a problem...and a low HP VFC is the cheapest way to go for that.

even if you have to purchase a couple of VFC drives and use them to do nothing except run the motors at 100% -> it is probably the least expensive option....just don't be tempted to vary speed...

I have been (still am) running my entire shop from a rotary phase convertor for 30 years and a good rotary convertor is just fine.... but not cheap...including a pair of CNC milling machines.

Although I have to admit that it does not like running from my Generac whole house generator...things act funny when I start the lathe...generator droops, phase convertor droops - lathe droops....generator catches up, phase convertor catches up - lathe catches up

eventually all stabilizes and I can get back to work...but it is something of which to be aware.

[John Hasler]

Add a flywheel to the phase converter.

[Steggy]

On the other hand, I just slapped a modern VFD onto 2 antique 3-phase motors and they're working just fine.
If they die, I'll replace them.
I run from 30% to 200%.
I don't load the motor too much at low speed and high speed makes me a bit nervous.

It will almost always work. The problem is antique motors' insulation sometimes doesn't handle the noise and hash on the VFD's output very well and eventually breaks down. You'll have no trouble telling when that happens.

Add a flywheel to the phase converter.

That should help, up to a point.

[armscor 1]

My circa 1955 Dean Smith & Grace had a 5 HP Crompton Parkinson 3 phase motor, heaps of iron, drove the guts out of it nearly everyday with a VFD for 6 years and never had a problem.