VFD vs rotary phase converter

[johndeeregreg]

in my last post about drill presses a while back guys were mentioning using phase converters or VFD's to open the option of 3 phase equipment into our single phase shop. some said something about you need to
up size them because you loose some power in the conversion process so my question is if i wanted to run a 2 hp 3 phase motor on a drill press what would be the best route to go and what kind of specs would i
need to have? if looking at a vfd do i need to search for a 3-4hp vfd to run a 2hp motor or do they factor the drop into the rating and a 2hp motor needs a 2hp vfd? which one is easier to set up and not have
issues with? i have talked to a couple local electricians that are generally pretty helpful and they more or less said I'm on my own to figure it out and to search google for my options.

said drill press is on an auction that ends on the 14th so not a lot of time to figure out if its a feasible option or if i should keep looking.

 

[Hemmjo]

I have a 1HP 3 phase motor on my lathe, I bought a 1 HP VFD phase converter. I have been using it for about 6 years now with no problems. You do loose some torque when you slow it WAY DOWN, but that has nothing to do with the size of the converter.

 

[buickanddeere]

The solid state VFD s provide true three phase power . The rpm , torque , current and direction are all easily controlled .
A 2HP VFD supplied with single phase/two live lines . is used on a 1 HP three phase motor that is supplied with three
Live lines . Not because of " lost power " .
At the same voltage and current . Single phase can only supply 57.7% of the power that three phase does .

 

[timcasbolt]

You won't lose power using a rotary phase convertor.

 

[buickanddeere]

. Can not obtain true three phase power from a rotary . The phase vectors are distorted in angle and amplitude .

 

[Stephen Newell]

Myself, I prefer a rotary converter. I bought one because I bought a machine which a motor wasn't available in single phase. Once I got the converter I was able to purchase more machinery and run all of them off the same converter. Of course I don't run all the machinery at the same time but I can go from machine to machine as though I had three phase. With a VFD I would have to have one for each machine. The rotary converter I have is rated at 7.5 hp and one machine has two motors, 5 and 3 hp. The other three machines I have are 7hp, 5hp and 3hp.

 

[Geo-TH,In]

A farmer a mile away converted all his irrigation pumps to 3 phase and used rotary converters.

I was told, not 100% sure, the converter is only about 70% efficient.
Again, I was told, hear say.

I don't think 70% is a big deal with a drill press.

 

[Geo-TH,In]

A good chance you can buy a 2 hp 220v single phase motor cheaper than a 3 phase converter.

 

[timcasbolt]

A static phase convertor costs you about 1/3 of your power, a rotary phase convertor does not.

 

[dr sportster]

The VFD is silent The phase converter not so much .This is a major factor if you listen to music whilst working { the VFD is a pleasure}

 

[Steve@Advance]

Yes, it is advised to go up to the next size VFD when operating as a phase converter. So for a 2 HP motor, go up to a 3HP VFD. You could probably get away with a 2 HP because you will most likely never load the motor to full capacity unless you plan on doing some very heavy work.

The only disadvantage to using a VFD is it will only operate one motor at a time, where a rotary converter can be connected to a 3 phase panel and operate several machines at a time using the original machine controls. It there are more than one 3 phase motors on the drill press (coolant, up/down servo, etc) then a rotary converter would be an easier option.

When connecting a VFD, you must control the start/stop/reverse with the VFD key pad or configure the original machine controls as remote inputs. You cannot simply wire it in to the original disconnect. There is a set up procedure but for a simple drill press operation it is not difficult to program.

 

[moresmoke]

I put a VFD on my 3hp Bridgeport Clone. I would do it again if I needed to. Wired the original switch to control the VFD as reversing took a couple button presses.

 

[wp6529]

Go with a VFD for variable speed, dynamic braking and lace of the noise, bulk and inefficiency of a rotary converter.

Read the VFD specifcations carefully on sizing and single phase input operation. There are VFDs that are single phase input only and require no derating, VFDs that will accept single phase input with derating and VFDs that will not accept single phase input.

 

[buickanddeere]

(quoted from post at 17:56:42 12/12/23) A good chance you can buy a 2 hp 220v single phase motor cheaper than a 3 phase converter.

Something turned roundabout there .
The solid state VFD runs with about 95% efficiency . A rotary converter is a stretch to obtain 70% efficiency .

 

[Butch(OH)]

VFDs are a very good option if you have one or two machines and the variable speed abilities would be beneficial. The other side is if you have many tools, or expect to have and don't need the variable speed option. I have a shop full of machine tools running from one 10HP rotory that cost me $500 to build.

 

[Ultradog MN]

I'm with Butch OH.
I bought a 3 ph lathe a few years ago and that required I come up with a way to power it.
A scrapper buddy of mine got me a 7 1/2 hp motor for free. So I went with a rotary.
I bought a 12'' x 14'' x6'' enclosure box off CL for $25
I bought the 7 1/2 hp kit from the outfit below.
It was simple to follow the wiring diagram that came with the kit.
Once I opened the door to 3 phase other machines came my way and I have several now.
I can power any of them with my one rotary converter.
Phase converter kits

 

[Ultradog MN]

I put my idler motor outside on the back of my garage. Can hardly hear it there.

 

[Butch(OH)]

Having one machine tool is like having rabbits. Be ready for multipication.

 

[Paul in MN]

I know I am late to this discussion, but I'll share my experiences for further consideration on this topic. I currently have 2 drill presses, a Bridgeport mill, and a large lathe which have 3 phase motors. I first began powering only one of the drill presses with a Baldor VFD (acquired as used, from a friend). It worked for about 6 months with the mill and the smaller drill press. Then when I started it up on the mill (no load), it blew up sounding like a 12 gauge shotgun going off in my shop. Friend (an Elect Engineer) said it was likely the internal capacitors that blew. He pronounced it as non-salvagable. So I found a hardly used American Rotary brand 5 Hp rotary phase converter on CL and bought it. It is well built and has been 100% reliable. Its power output is smooth enough to run Computer Controlled machines, but for my purposes it would hold the safety start relays fully engaged on my machines. I added the bigger engine lathe to my shop and upgraded to a 15 Hp American Rotary converter, new with lifetime warrantee. Due to personal issues I have not installed the bigger one yet, but hope to soon. Look at Keith Rucker's U-Tube channel for 10% discount on American Rotary products.

 

[wp6529]

[Lto be clear, both the VFD and the RPC use large elwctrolytic capacitors that will eventually fail. You cannot reasonably compare the reliability of a barely used RPC with that of a used VFD that may have had thousands of hours of run time in industrial use before you got it. Most any quality new VFD placed in non-production machine tool service will outlive you as will a new RPC.