VFD, rotary phase converter or motor swap to single phase?

[rabler]

Can a VFD not be used to simply convert the single phase to three phase to power the unit without having to get into other wiring issues in the lathe? I really don‘t want to complicate the setup of the lathe.

To expand a bit on my earlier comment with a crude analogy:
A VFD is not a simple power supply, it acts a bit more like the cruise control on a car. It monitors the speed and adjusts the motor power (voltage/current) accordingly. Imagine driving on cruise control at highway speed and slipping your car into neutral unknown to the cruise control. As the car slows down the cruise control would keep giving the engine more fuel until it over revs and if left that way bad things happen.

Slipping the car in neutral is equivalent to having any sort of control or switch between VFD and motor.

VFDs are nice if you want adjustable speed. They also significantly reduce the startup current to a motor. And they are not horribly expensive. I retrofitted one on my 3HP lathe, no regrets. Plenty of help here for doing it. But if you want the shortest path to using the machine get a phase converter. I’ve done both. I downgraded my 20HP lathe to 10HP and used the 20HP motor to make a rotary phase converter.

 

[projectnut]

Simplest and cheapest is static phase converter. I bought one as a stop-gap until I got my rotary converter. Still using it 4 years later.

WNY Supply Online store for static phase converters

There is a reduction of power of about 1/3 when using an SPC.

VFDs can be had relatively cheaply but are not as simple.

I'm in the same camp. I started with a static converter on a 1 1/2 hp Bridgeport 22 years ago. I went with it rather than a VFD or a rotary converter because of cost and ease of installation. I now have 4 machines running on static converters, and a 15 hp rotary converter that's been setting on the shelf for nearly 6 years because I see no need to install it.

Static converters generate the third phase using a set of capacitors. Once the motor comes up to speed they drop out and the machine essentially runs on single phase. There is supposedly a 1/3 loss of hp, but in over 20 years I've never needed more hp on the mill or any of the other machines. They are extremely simple to install. The last couple I did took less than 15 minutes each. They also allow you to use the original machine controls without any modification.

Static converters are also inexpensive compared to the other options. The first static converter I purchased was from Phase A Matic. It's been extremely reliable, but is probably the most expensive on the market. All the converters are either from American Rotary or North America Phase Converter company. I have 2 from American Rotary and one from North America. Several years ago American bought out North America and transferred all the static converter production to that facility.

Static Phase Converters | Static 3 Phase Converters for Sale

Get consistent motor power with a static phase converter! These American-made converters are designed to operate 3 phase motors on single phase power.

www.northamericaphaseconverters.com

If you're new to the game or money is a factor I would definitely go with a static converter. Any of the other options will incur either substantial cost and/or significant time and knowledge for installation. The main reasons I haven't installed my rotary converter is the fact that all the machines run just fine on their static converters, and I don't want to spend the time and money to rewire the entire shop.

As an FYI I do use all the machines with static converters on a regular basis. The mill gets used an average of 15 hrs. a week. There have been times when I had big jobs to get out the door and it's run over 60 hrs. in a week. I also have one on My 2 hp Sheldon lathe, my 1 1/2 hp Racine power hacksaw, and my Black Diamond drill grinder. The lathe averages 10-15 hrs. per week, and up to 30 hrs. per week. The saw is about 3-5 hrs. a month, and the drill grinder is an hour or so a month.

 

[Eddyde]

Harrison M-300, Nice lathe by the way!
To reiterate what others have said, from my perspective:

1. "Simplest cheapest way" is a Static Phase Converter, which is basically a couple of capacitors wired in parallel with the motor. This gives you about ⅔ the rated hp, so for your 3hp lathe you would get about 2hp. IMHO that would be plenty of power, especially if you are starting out; I ran my South Bend Heavy 10 that only had a 1hp motor off a SPC for years and never felt lacking in power. SPC can be bought for around $100 or easily made for around $20.

2. Th next more expensive* option is the VFD. As others have said, the power output must be wired directly to the motor and the lathe's control switches, stop/start, forward, reverse and any safety interlocks, must be wired directly to the VFD's control inputs. I did this for my mill and it was a bit of work to wire it up but it functions perfectly.

3. The most expensive (*unless you build one yourself) is the Rotary Phase Converter, This will give you full power, plug in play convenience and the ability to power more than one machine. This is the option I went with when I got my 13" CC gear head, I wound up building my own and using it to power the SB lathe, a drill press and a washing machine.

You can also start out with a SPC and convert it to a rotary by adding a three phase motor.
Here's a good article on the basics.

 

[Beckerkumm]

That lathe is a pretty nice machine. When deciding on vfd vs rpc ( single phase or static is out in my world ) you also want to look at the speed options. If the changes are fairly linear with speeds where you want them, an rpc is the easiest. Some lathes have a lot of low end speed choices but large ranges at the top. Those lathes really benefit from the vfd to dial in the SFM. If you have a good machine with little wear that still cuts with some precision, be good to it and make it perform to it's capabilities. Often a vfd makes a high speed lathe better, but not always. Cost either way is in the 500-1000 range depending on how good your scrounging skills are. Dave

 

[BEI]

I do appreciate all the input from you guys which is why I posted the question. Regarding the static converter, my lathe has a speed range of 45 to 2500 which I think will be quite adequate for anything I’m likely to want to do. My reservation with a static converter is the loss of 1/3 the power and won’t I miss that if I want to make heavy cuts when turning steel? Steel is what I intend to work with the most, not aluminum or plastics. With no experience I’m going on info I’ve gathered from the ‘learning channel’, YouTube.
The variable speed option of a VFD is attractive but, to me, just icing on the cake that isn’t needed unless I’m missing something, which very well could be the case. If so, please clue me in.
The rpc is attractive for the simplicity and utility for other machines but the cost is kind of steep compared to the other options.

 

[MrWhoopee]

Something I forgot to mention is the power consumption of an RPC. You have a motor larger than the machine you are operating running continuously, plus the draw of the machine itself. I have a 7.5 hp RPC (for sale), which I used it for about a month. I objected to the continuous whine, mama objected to the electric bill.

 

[Winegrower]

There is supposedly a 1/3 loss of hp, but in over 20 years I've never needed more hp on the mill or any of the other machines.

My reservation with a static converter is the loss of 1/3 the power and won’t I miss that if I want to make heavy cuts when turning steel?

A TV lawyer might say “asked and answered.” I tell you, my 3HP lathe is on a static phase converter, which also works the Bridgeport mill, the Kalamazoo 9”x16” horizontal saw and the Jet vertical bandsaw. I cut metal a lot, and have NEVER encountered a lack of power in any operation, nor even heard the slightest audible change in power. Anything near any power limit is preceded with an incredible amount of blue hot flying chips that are too uncomfortable for me to press on harder. The tools seem to me to limit usable power before the phase converter does.

I think this loss of power point is highly overrated, at least for my reasonably aggressive use of the equipment.

 

[rabler]

The rpc is attractive for the simplicity and utility for other machines but the cost is kind of steep compared to the other options.

The budget way of building an RPC is to buy a RPC panel, and then get a used three phase motor, perhaps from Ebay, to use as an idler.

 

[Shootymacshootface]

The budget way of building an RPC is to buy a RPC panel, and then get a used three phase motor, perhaps from Ebay, to use as an idler.

This is what I did and couldn't be happier with my arrangement.

A friend gave to me, a 5hp 3ph motor from an air compressor. I build a simple non balanced RPC with a pony motor to start it. It worked, but I wanted the convenience of push button start and I felt as though my surface finishes would improve slightly if my RPC was balanced. I bought a complete control panel from WNY Supply for a little over $100, and like I said, I couldn't be happier with it. I honestly don't know why someone would spend over $1000 on an RPC when they are so easy to build like that.

Converting your machine to single phase would be a mistake. Although, not having any experience with a 3ph machine, you wouldn't miss the instant reversing and a few other benefits that I can't think of right now.

 

[BladesIIB]

I will add my two cents here. The VFD may seem cheaper but it is close to the same cost all in as a RPC for the 3HP size you are looking at. By the time you buy the enclosure and extra wiring etc. that you need in addition to the VFD you may find you are near the cost of the RPC. That said, in addition to being able to use a POT for speed control. With a VFD you also get ramped electric start up and controlled electronic braking which will stop your spindle a lot faster. You can add a switch and have a couple of different start and stop speeds as needed. For plug and play I would say your best option is the RPC. The VFD is great and I love mine but as others have mentioned the learning curve is an investment up front. I have a video on YouTube with all my learning from mksj and setting up my VFD. If you are interested you can find it in the site or PM me and I will send you a link to it. All the best.