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



## BEI (Mar 18, 2022)

I have been lurking on this site for a few months trying to get some understanding of what‘s involved in machining. Machining is a hobby that I am taking up in my retirement with absolutely no experience and am now awaiting the delivery of a new to me Harrison M300 lathe with a 3hp three phase motor. It is a gear head with an ample range of speeds for anything I am likely to try. Having said all that I need to know what will be the best way to convert the single phase 240v in my shop to three phase for the lathe when it gets here. Or should I swap the motor out for a single phase? What’s the simplest and cheapest way to get it up and running? Don’t think I’ll need any other options like variable speed. Some advise from some of you guys with experience would be much appreciated.


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## MrWhoopee (Mar 18, 2022)

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.


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## rabler (Mar 18, 2022)

Any of the three will work.
Buying a rotary phase converter is the simplest but probably not cheapest. It does cover other possible (future) machines.
VFDs are relatively cheap but take some work to install as all the on/off/forward/reverse control needs to be done by the VFD, so rewiring the controls is necessary.  A motor swap is usually the least desirable approach.  Single phase motors do not have uniform torque as they turn, this can impact surface finish .


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## BEI (Mar 18, 2022)

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.


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## rabler (Mar 18, 2022)

BEI said:


> 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.


In short, no. 
VFDs are meant to control a motor, completely, entirely, and with no other mechanism interfering with how they interact with the motor.  You tell the vfd what you want (via electrical inputs), it makes the motor do that.  Trying to get around that is not completely impossible but isn’t practical and can easily result in a dead vfd.


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## Dabbler (Mar 18, 2022)

@BEI @rabler  is quite right.  You have a 3 phase machine.  All of the electrics in the lathe are expecting well behaved 3 phase power. unless you want to rewire the machine.  It can take considerable effort to do so.

You can NOT just use a VFD to 'create' 3 phase power for you.  It depends on motor feedback to start (and stop) the motor.   You can also not wire it between the lathe controls and the motor.  It will not work correctly unless it is permanently attached to the motor it controls.

@MrWhoopee and @rabler have the right of it.  Go static or rotary, and your machine will work as it is intended to.  Go with a VFD and you are in for a world of work.  One of my friends converted a 1PH machine to 3PH with a VFD, and took about 80m hours to rewire it.  He is a competent electrical tech.

I have rotary converter, VFD, single phase and a static converter in my shop.  *I would choose a 5HP rotary for your lathe.*  Every time.  It will also 'future proof' your shop in case you get a 2 or 3HP 3phase mill or surface grinder.

My rotary converter is 15HP, but I have bigger machines.  I run one machine off of a VFD and have installed 5 others for other people.  I have a milling machine in another shop that is on a static, but it has reduced the torque noticeably.  Two of my machines are single phase.  (Yes I have too many machines)

A very good static converter will preserve over 70% of the torque, but a lathe needs all the starting torque you can get, hence the rotary.


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## Watchwatch (Mar 18, 2022)

Buy a rotary phase. American rotary is a great option. You’ll be able to use it to power other machines in the future.


Sent from my iPhone using Tapatalk


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## Dhal22 (Mar 18, 2022)

Yes on rotary phase.   I tried the digital converter and could not get the lathe to start.   Adding a mill soon so glad I ended up with rotary.


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## Nutfarmer (Mar 19, 2022)

If you just want to run a 3 phase motor a vfd is the way to go. I have one on my surface grinder and it works great. I have a Hartinge lathe that has a two speed 3 phase motor and I chose to use a rotary phase converter to run it. I didn't want to rewire the entire lathe. It all depends on what you have and what you want to do.


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## AGCB97 (Mar 19, 2022)

As @Nutfarmer said, A VFD is the way to go. Rewiring is as easy as cutting the plug off the machine and sticking the wires in the VFD. Put the lathe switch in RUN/FORWARD, put a bag over it or tape it so you never touch it again. Spend a little time learning to set the VFD controls (once and done forever). Lots of help on this site for that last step.

Cheap, easy and satisfying!

I have 4 of them so far. Just yesterday, I was threading a 1 1/2" - 16 shaft that was sticking out of the chuck only 5/8". Using the speed control of the VFD, I was able to speed up to get to the number on the thread dial and then slow down to watch closely the tool advancing to the chuck. Stopped less than 1/8" from crash. I don't think you can do that with an RPC or SPC.

My seasoned opinion respectfully submitted.

Aaron


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## rabler (Mar 19, 2022)

BEI said:


> 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.


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## projectnut (Mar 19, 2022)

MrWhoopee said:


> 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.
> 
> 
> 
> ...


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 | Electronic Phase Converters | NAPCco
					

Get consistent motor power with a static phase phase converter! These American-made static phase converters come with an included lifetime warranty.




					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.


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## Eddyde (Mar 19, 2022)

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.


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## Beckerkumm (Mar 19, 2022)

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


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## BEI (Mar 19, 2022)

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.


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## MrWhoopee (Mar 19, 2022)

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.


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## Winegrower (Mar 19, 2022)

projectnut said:


> 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.





BEI said:


> 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.


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## rabler (Mar 19, 2022)

BEI said:


> 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.


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## Shootymacshootface (Mar 19, 2022)

rabler said:


> 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.


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## BladesIIB (Mar 19, 2022)

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.


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## projectnut (Mar 19, 2022)

Winegrower said:


> 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.*


I would agree.  I have a static converter on my 2 hp Sheldon 13" lathe.  It has a speed range from 60 to 2,200 rpm.  I often cut mild steel with HSS tooling at a depth of .125" and have on occasions gone as deep as .187" when I'm in a hurry.  I've never had the motor even slow down let alone stall.  I have had the belts slip if I really get carried away.

I have on occasion cut 6061 aluminum at a depth of .250 just to see if it was possible.  The lathe doesn't complain, but it seems like it's beyond the practical limit.  It seems safer and more practical to limit it to .125" or less


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## BEI (Mar 19, 2022)

MrWhoopee said:


> 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.


How is your rpc configured, for outdoor running or in the shop? Does it’s control box sit on top like some American Phase machines or does it require wall mounting? Who makes it and what are you wanting for it?


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## BEI (Mar 19, 2022)

Winegrower said:


> 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.


Didn’t mean to offend. Perhaps I should have asked first if you made heavy cuts on steel before I asked. Wasn’t meaning to dismiss your input. Can you tell me which brand of static converter is the most reliable and long lasting? Thank you for your help.


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## Winegrower (Mar 19, 2022)

BEI said:


> Didn’t mean to offend.


Ha ha, is that even possible??    



BEI said:


> Can you tell me which brand of static converter is the most reliable and long lasting?



Really, I can only say that I have bought 5 Phase-A-Matics (while helping friends), and all worked fine and still do.   These were the better priced of the units I considered.
There's not that much to go wrong.


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## BEI (Mar 20, 2022)

rabler said:


> 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 sounds like a doable and less costly option. It raises a few questions though. First, can I use a 3hp motor as the idler (the same hp as the lathe) or must it be larger? Second, is the idler motor speed important? Does it need to be same speed as the lathe? And, since I don’t know what an inverter type motor is, I wonder if I can or cannot use such a motor? I took a look on eBay and there appears to be a few at reasonable cost available but what is needed?


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## Dabbler (Mar 20, 2022)

Your idler motor must be at least 30% larger in HP than your starting motor for normal applications.  For a lathe it is recommended that it be at least 50% higher, because of the high current draw associated with starting the gearbox and chuck.  My 7.5HP lathe is fed by a 15HP rotary converter.

[edit]  You do not *need* an inverter duty motor.

as I posted in an earlier post, use a 5HP rotary converter or higher.


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## rabler (Mar 20, 2022)

As @Dabbler said you need to oversize the rotary phase converter.  You’ll want a 5HP converter, (or larger) which means it uses a 5hp motor as an idler.  As long as it is a 3phase 220V motor, rpm doesn’t matter, and whether or not it is inverter rated isf also not important.  Lower rpm motors may be quieter/less of a background noise source.


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## Dabbler (Mar 20, 2022)

I honestly don't understand the problem with rotary converters and noise.  Having worked in woodworking shops over a 50 year span, they are much quieter than any cyclone dust collector, table saw or even bandsaw...

The guy I bought the converter from had it in an outdoor 'doghouse' - not the best place for capacitors to live for 40 years (we get -40 degrees here most winters).


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## BEI (Mar 21, 2022)

Thank all of you for your advise. Given what I’ve read from you, I’ve decided to go with a static converter with the option to make it an rpc if desired. The VFD option is not completely off the table but that can always be done somewhere down the road if I find myself wanting the control options a VFD offers. The North American static converter should be here by the end of the week. Again, thank you.


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