Can a VFD be used to just provide 3ph Power?

[macardoso]

I'm only concerned with the Lathe. The other 2 machines are on small VFD's as I want the variable speed and do not have all the start/stop needs of the lathe and it's wiring. I was contemplating a re-wire of the lathe but believe I will make my life hell trying to wire in all the braking and direction changes needed in typical machining. The hand switch on the carriage also scares me - that I'd lose that function.

The relays and switches internal to the lathe presumably work already - feeding "simple" 3 phase and using the existing wiring seems to be the most straight forward solution. At this point it looks like a rotary or (most likely) static or digital converter is what I should have gone with (already have the VFD on order, so I think it'll go back).

In hindsight, if I had seem my collection of 3ph tools growing like it did - I probably would have invested in a rotary converter in the first place.

Sounds like a good plan.

I will say that you absolutely can keep all the original switches, including the start/stop lever on the carriage. I have done exactly that. Basically you rip out all the existing wiring and bring all those switches back to the VFD as digital inputs.

Keeping the lathe as-is and going to a phase converter is perfectly acceptable as well.

 

[Eddyde]

Thanks for the insight. Given the cost, size and complexity of the rotary converters (in my case primarily the cost), and I this is purely a hobby for me at the moment, would a digital or static phase converter and take the HP reduction be a reasonable middle ground and still provide the 3ph feed the Lathe needs?

Yes, I ran my South Bend Heavy 10 on a static converter for years and never felt a lack of power, the belt would slip before the motor would stall. It only has a ¾ hp motor thus was only giving around a ½ hp.

I built my Rotary converter for only a couple of hundred bucks. You can use the static converter to eventually build a rotary converter simply by adding in a second 3 phase motor and a couple of capacitors.

 

[Assiniboine_Iron]

Yes, I ran my South Bend Heavy 10 on a static converter for years and never felt a lack of power, the belt would slip before the motor would stall. It only has a ¾ hp motor thus was only giving around a ½ hp.

I built my Rotary converter for only a couple of hundred bucks. You can use the static converter to eventually build a rotary converter simply by adding in a second 3 phase motor and a couple of capacitors.

That's my current line of thought. I'm going to build the Static converter. I don't have another 3hp 3ph motor - but if I find I'm running out of HP on the lathe I have (Taiwan version of a Victor 1340GHE), I'll dig deeper into making the rotary converter. Both are surprisingly simple and I'm not an electrical guy... though I never would have figured either out without youtoob...

 

[mksj]

A few things o consider using a static converter vs. VFD on a lathe, with the latter you get controlled acceleration and electronic braking, so much more predictable. Even with a mechanical brake, I rarely use it and let the VFD do the braking. It is often advantageous to dial in the spindle speed on the fly to decrease chatter/get more ideal chip formation. In some cases surface finish may be different, but depends on many factors. Installing a VFD with a direct connection to the motor is not much more difficult then on a mill, but there are certain recommended safety considerations so the lathe cannot restart if you have a sustained run command. How this is implemented varies by VFD and programming parameters. A static converter is a quick inexpensive approach, be sure that the generated leg is not used to power the transformer/electrics.

 

[Assiniboine_Iron]

A few things o consider using a static converter vs. VFD on a lathe, with the latter you get controlled acceleration and electronic braking, so much more predictable. Even with a mechanical brake, I rarely use it and let the VFD do the braking. It is often advantageous to dial in the spindle speed on the fly to decrease chatter/get more ideal chip formation. In some cases surface finish may be different, but depends on many factors. Installing a VFD with a direct connection to the motor is not much more difficult then on a mill, but there are certain recommended safety considerations so the lathe cannot restart if you have a sustained run command. How this is implemented varies by VFD and programming parameters. A static converter is a quick inexpensive approach, be sure that the generated leg is not used to power the transformer/electrics.

Understood on the VFD for the lathe. some of what you say is why I'd like to try the Static Converter - aside from the HP reduction the lathe with operate how it was intended. For my mill, i like that the VFD gives me speed control with out screwing around with belt changes but on the mill i only start, dial in a speed and then stop when done... with the lathe it is a LOT of starting and stopping and some of the hand controls, pump, lights etc would also need to be wired up. I'm going to give the SPC a try, if I need the full 3HP I'll look for a motor to build a rotary converter, and if all else fails I can still strip it out and re-wire with a VFD, brake resistors and 110V accessories.

 

[markba633csi]

Check what other devices need power on your lathe besides the main motor- if there is a step-down transformer see what type of power it is expecting. It may be necessary to reconfigure the input taps and/or run a separate power feed from a 120 volt outlet in some cases