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VFD or Phase converter

brncofan

Plastic
Joined
Oct 15, 2023
good evening i just purchased a bridgeport mill with 1 hp motor and a Grazioli Lathe with a 2HP motor iwas wondering what would be better a rotary phase converter or VFDs ? im kinda leaning towards a American Rotary rotary phase converter anyone here help me decide or should i go VFD ? if so what brand? appreciate any feedback Mark
 
Those are small enough motors that'd I'd buy individual drives. The 1hp unit can even be purchased with 115v input, then your wiring costs basically amount to an extension cord.

The RPC is nicer in some aspects, but aside from purchase cost the wiring can really add up.

For a brand, there's tons of options in that size but I'd go with a TD200 from Factorymation or a Durapulse from Automation Direct. Both companies have been very easy for me to deal with over the years.
 
Just an FYI but there is a subforum for VFDs and such.

For me since I only use one machine at a time I have a Hitachi WJ200 series sized for the largest motor and use twist-loc plugs to switch to the one needed.
 
I am a rotary phase converter fan myself. I have American Rotary units and they have been problem free. FYI if you go that route.
Same. My AR phase converter works great for me but I have a 1.5HP J head, 3HP hydro power pack for the mill and a HLV lathe running in it. I went 10HP which is overkill for my current needs.
 
One 5 Hp RPC is all you need. The simple one you can make yourself is a 5 HP 3 phase motor and a 2 pole switch for the incoming AC.
When you buy a RPC and open the panel up you will see how simple this all is and regret buying instead of building.
If you can drive a car then you can connect a few wires. Later on you can add a start switch and a couple of capacitors.
 
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good evening i just purchased a bridgeport mill with 1 hp motor and a Grazioli Lathe with a 2HP motor iwas wondering what would be better a rotary phase converter or VFDs ? im kinda leaning towards a American Rotary rotary phase converter anyone here help me decide or should i go VFD ? if so what brand? appreciate any feedback Mark
"Best" is heavily dependent on what you want.

"Simplest" is another way to look at the issue.

A VFD is not going to be the simplest, because you will need to completely redo the machine controls, unless you are willing to ignore the original controls, and do everything via a new control panel, or with the buttons on the VFD.

The "simplest" (or "easiest") is something you can connect the machine to and run it as-is with no changes.

Some form of RPC, will be the simplest/easiest as far as the machines. No modifications to the machine are required. You just plug in the machine to the RPC and go. No features are added, but the machine runs as-is, just as it was designed to do.

You can buy an RPC complete, or you can put one together from a "kit" (normally the controls only, you supply the idler motor). You can build it from the motor plus purchased parts. The simplest RPC is just an oversized 3 phase motor with some mechanical means for starting.

Then there is is a VFD. Going that route will mean at least some modifications and re-wiring of the machines. The amount of modification depends on whether the original machine controls are used. It does give you variable speed, which you may consider to be a benefit if the machine has no provision for that already.

Your choice may depend on how much you want the variable speed that the VFD can provide, and how much hassle you are willing to put up with to get it.
 
I recently finished building my second rotary phase converter. This one was for a friend of mine.
Here is an approximate itemization of the costs.
5 hp motor off of Craigslist - $50
Phase converter kit with the capacitors and contactors from the outfit at the link below. $80
A 12x16 enclosure box. $40
Some scrap metal, screws, bolts, welding rod, wire, electrical connectors and paint/primer, etc. $30
Total - about $200
The first one that I made for my own shop about 2 years ago has a 7 1/2 hp motor and cost me less because I got the motor for free.
The instructions I got with the kits were clear and simple - and I'm no electric guru. I now have six 3 phase machines in my shop and it will run any of them.
And as a test I have idled my 3 hp lathe, 1 1/3 hp mill and 1 hp bandsaw all at the same time.

 

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I suggest AC servo motors with timing belt transmissions.

It´s what I did to my 2 HP lathe with outstanding results, after trying pretty much everything else.
Bad:
It´s expensive.
A HTD-8 belt at 30 mm wide, is not cheap, nor are the pulleys.
The 2.5 kW servo system runs about 1500€.
(1:3 pulleys 8x30 mm - 24:72) 200€).

Good:
1. Endless torque.
About 90 Nm from 0-1000 rpm.
(peak, 3 secs, plenty).
1.1 !! Much more torque than original very good, 1.5 kW industrial motor with belts.

2. FANTASTIC surface finishes with variable surface speed.

3.
No crash.
The servo faults before breaking anything.
About 0.008 seconds.
Seen many (5) times.

4.
No belt changes.
Adjustable surface speed, feeds, rpm.

The best things are the crash protection, and surprisingly to me the torque.

I never thought I wanted more torque, but it´s about 3x faster and better than it was, to my great surprise.
The no-belts and any-rpm are wonderful.

The HAAS ST10 lathe, 40.000€, 10 kW, has about the same torque (102 Nm peak, 1200 rpm) as my 1.5 kW-original or 2.5 kW-AC-now servo lathe.

VFD.
A VFD is wonderful for soft-start and wide rpm, and low noise, especially with a biggish quiet motor.
Nice reverse, soft starts/reverses, pretty good stability normally.
Can give high rpm, when needed.
Not expensive upto 3 kW or so.

RPC.
An rpc with a quiet biggish industrial motor is wonderful for torque, low ripple, good surface finish.
Cheapish, reliable, simple.

AC servo is by far the best, but the most expensive.
It´s also a bit noisy, if using timing belts, but these give spindle encoder, rigid tapping, c axis positioning, perfect sfm (electronics needed, $$$).

For limited budgets I would probably recommend an oversize 3-phase motor, and a VFD.
The motors cost almost nothing extra, and the extra torque and any-rpm via potentiometer are extremely useful.
So is soft-start, and soft-reverse, and estop.
And less or perhaps no belt changes.

Here in the EU a 3-5 kW motor for a lathe is not really much more expensive than 1.5 kW.

5.5 kW, very high torque.

350 €, 1500 rpm.
You can run them at 3000 rpm for reasonable times/loads.

Perhaps 300 € for a VFD, box, switches, cabling, stuff, mount.
Around 800€ in materials.

The bigger motor of lower rpm is likely to be quiet, will last a long time, with low/no heat, and will give excellent surface finishes, typically.
It´s a bother to do the mount, and figure out the wiring.
So is anything else.
It´s also likely 3x better than the original motor.

My *experience* and opinion is that a VFD with industrial motor is vastly better than the homebrew stuff sold for "lathes" from typical chinese importers.
(mine).
An industrial motor like a Bridgeport original 3-phase with belts is also very good.
(mine).
And industrial motor for a "proper" lathe with belts is also very good.
(mine).

An AC servo drive, 220 V, driving a good transmission via timing belts, is the bees knees.
It makes the lathe very very much better.
But it was very expensive, all-in, (expensive electronics), and worth it for me but probably not for many users.
And very heavy mounts, stuff, 100+ hours, for the belt drive.
 
One 5 Hp RPC is all you need. The simple one you can make yourself is a 5 HP 3 phase motor and a 2 pole switch for the incoming AC.
When you buy a RPC and open the panel up you will see how simple this all is and regret buying instead of building.
If you can drive a car then you can connect a few wires. Later on you can add a start switch and a couple of capacitors.
IMHO, you highly overestimate the abilities of most people that drive.

That said, a very basic rotary is pretty simple to wire up.
 
People mess up 2-way/3-way lighting, too. That's only five wires. You're also omitting a starting method.

I don't think a VFD is really any simpler, though, even disregarding the controls.
 
Do you need to have an Isolation Transformer between a RPC and a CNC machine?
1) Do you need a neutral? 2) Does the machine have MOVs or other similar overvoltage protection on the mains input?

If yes to # 1, then yes you need a transformer, with wye output.

If yes to # 2, then a wye output transformer is one way to fix the issue, but it depends on how the voltage protection is connected.

If it goes to ground or neutral, then either use a transformer or disconnect the voltage protection.

If it is only line-to-line, then you can probably get away with leaving it and not using a transformer.

It would be a good idea to check with the manufacturer. They know more than we do about their product.
 
1) Do you need a neutral? 2) Does the machine have MOVs or other similar overvoltage protection on the mains input?

If yes to # 1, then yes you need a transformer, with wye output.

If yes to # 2, then a wye output transformer is one way to fix the issue, but it depends on how the voltage protection is connected.

If it goes to ground or neutral, then either use a transformer or disconnect the voltage protection.

If it is only line-to-line, then you can probably get away with leaving it and not using a transformer.

It would be a good idea to check with the manufacturer. They know more than we do about their product.
Thank you.
 








 
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