Rotary or frequency drive phase converter?

Fred.Rowe

Fred.Rowe

Knifemaker / Craftsman / Service Provider
Joined
May 2, 2004
Messages
6,848
I am in the process of upgrading my 2x72 grinder, by adding a 3hp, 3phase motor, replacing a 1 1/2 horse, single phase, motor with step pulleys.
I would like to get two things in the switch; more SFM[ I am currently running 3750 SFM] I would like to run 5000+ and more torque.
I understand that if I purchase a frequency drive VFD to run the new 3phase motor, I will also get variable speed with this type. Is there any down side to this type of converter?
If I purchase a rotary converter, I will not get the variable option and so will have to run, step pulleys. Is the rotary converter a better unit in the long run?
I will be getting a 3ph surface grinder next year and will power this through the same converter as the one operating the belt grinder.
If you can give me some insight, I would be most appreciative, Fred
 
Fred,
Better ask Rob over at Beaumont. He has this stuff down. From what I can recall, he advised me that VFD's can get quirky above 2 HP. I have been researching this subject quite a bit, because I want to throw a 5 HP on a KMG that I'm just setting up. If I have to go with a 3 Phase 5 HP motor, I'll be getting a rotary phase converter....I heard that they are much better than the "static" ones.
- Mitch
 
why buy a new motor for 3 phase and a convertor? why not just buy a single phase motor with the speed and HP you need?
 
sunshadow said:
why buy a new motor for 3 phase and a convertor? why not just buy a single phase motor with the speed and HP you need?
Click to expand...

That is exactly what I'm going to do; the only thing with a 3 phase motor, is that there are more models available.
- Mitch
 
Troop, I have a 5 HP single phase 220 motor on my metal lathe it works beautifully, I have it supplied through a 3o amp 220 receptacle. I would never buy a new 3 phase motor and try to convert single phase to operate it, the only reason I could see for converting (and the inefficiencies and losses involved in converting) is if you buy something that already has a 3 phase motor and converting is cheaper than buying a new motor.

-Page

Seems troop and I were replying to each other at the same time :)
 
sunshadow said:
Troop, I have a 5 HP single phase 220 motor on my metal lathe it works beautifully, I have it supplied through a 3o amp 220 receptacle. I would never buy a new 3 phase motor and try to convert single phase to operate it, the only reason I could see for converting (and the inefficiencies and losses involved in converting) is if you buy something that already has a 3 phase motor and converting is cheaper than buying a new motor.

-Page

Seems troop and I were replying to each other at the same time :)
Click to expand...
Page, what brand would you recommend? I've been looking at Weg's. I hear down in South Africa they like them.:D They're pretty reasonably priced, although I think they're made in South America.
- Mitch
 
sunshadow said:
why buy a new motor for 3 phase and a convertor? why not just buy a single phase motor with the speed and HP you need?
Click to expand...

I will be getting a 3phase 3hp surface grinder in Feb. The converter will supply power to both grinders. I also have a supply of three phase motors.

Fred
 
Troop said:
Fred,
Better ask Rob over at Beaumont. He has this stuff down. From what I can recall, he advised me that VFD's can get quirky above 2 HP. I have been researching this subject quite a bit, because I want to throw a 5 HP on a KMG that I'm just setting up. If I have to go with a 3 Phase 5 HP motor, I'll be getting a rotary phase converter....I heard that they are much better than the "static" ones.
- Mitch
Click to expand...

I figure Rob will give me his input on this when he logs on. I'm running a KMG grinder.

Fred
 
My LeBlond lathe has a GE, I'd imagine they're not cheap! Everyone on this list seems to source their motors from surplus center since I haven't had to purchase anything over 1 HP recently I'm probably not the best one to ask about brand. When I needed big motors in the past I usually went to a local shop that rewound electric motors and bought used/rebuilt. Never had any problems, and I saved big bucks. The shop I used to deal with in Ithaca is out of business, but I'm sure that it shouldn't be hard to find a similar shop near you (I know Syracuse has an electric motor repair shop and I am sure you are close enough to downstate that there should be one in your area)

-Page
 
sunshadow said:
My LeBlond lathe has a GE, I'd imagine they're not cheap! Everyone on this list seems to source their motors from surplus center since I haven't had to purchase anything over 1 HP recently I'm probably not the best one to ask about brand. When I needed big motors in the past I usually went to a local shop that rewound electric motors and bought used/rebuilt. Never had any problems, and I saved big bucks. The shop I used to deal with in Ithaca is out of business, but I'm sure that it shouldn't be hard to find a similar shop near you (I know Syracuse has an electric motor repair shop and I am sure you are close enough to downstate that there should be one in your area)

-Page
Click to expand...

Page, Ya know...I never thought of that. Good idea..a rebuilt motor shop! Why not, right? Thanks.
- Mitch
 
Fred

I would suggest you go the VFD route. As you have already figured out, you get variable speed with the VFD, not with the rotary converter. The rotary converter will be much larger and heavier than a VFD with the same rating. I had asked the Motor R&D Manager here at work about rotary converters for a previous thread. He said that the output from a rotary converter is not a proper three-phase, decreasing the efficiency of the motor that you are trying to feed. Also, the input power to output power efficiency of the rotary converter is likely to be something like 60-75 % vs well over 90% for a VFD. This reduces the amount of electrical power available to your motor, assuming the same input power capacity. Cost-wise, VFD prices are continually falling due to technical advances. Rotary converters consist of a big three-phase motor with a couple of capacitors and the only way to reduce costs is to cut corners on quality. Lastly, since the rotary converter contains an electric motor, you have the mechanical maintanance issues to deal with. I would expect rotary converters to dissapear from the market in the next few years.

It should not be difficult to use the same VFD to run more than one piece of equipment. Make up a distribution panel with a breaker for each motor you are going to feed.


Troop

The WEG motors are made in Brazil. Our Motor R&D Manager thinks they are of good quality, comparable to the brands made in the US. Yes, you can get VFDs rated above 2 hp. I am currently designing a range with ratings between 150 and 500 hp.


Phil
 
Fred,

VFD is the only way to go! Rotary converters will cost as much or more than a good VFD and won't give you the speed/directional control that is so nice to have and as Phil said the VFD's are much more efficient.

You can easily run multiple motors off one VFD (one at a time) and have speed/directional control as needed on each. I am curently running two belt grinders, one disc grinder, and my surface grinder on one VFD. Works GREAT!

PSO,

Don't know about the quality of WEG motors now but a few (10??) years ago we tried them at work and found them to be junk. They were not allowed back onto the plant site. May well be better today.......

-Mike-
 
Guys, I've been looking around at some sites and haven't seen too many VFD's that run with a single phase 220 input above 3 HP. Could you guys recommend some sites that have these? I sure would appreciate it.:thumbup: Thanks.
- Mitch
 
Mitch

Go and read M Spangler's thread about Rotary Phase Converters for an explanation.

http://www.bladeforums.com/forums/showthread.php?t=513096

Here are a bunch of 3 hp VFDs, some with single-phase inputs. The more expensive ones have control schemes built into the software that you probably will never use.
http://www.driveswarehouse.com/show...Horsepower=3.00&IVoltage=&OCurrent=&x=16&y=12

Otherwise, get a VFD rated for at least 5 hp, with a 3-phase input, to run your 3 hp motor. Set the current limit levels on the VFD to the motors nameplate current. They have ratings that are 67% higher than the 3 hp VFDs but only cost about 20% more.
http://www.driveswarehouse.com/show...&Horsepower=5.00&IVoltage=&OCurrent=&x=20&y=6

I have no direct experience with the Hitachi and LG brand VFD's sold by driveswarehouse but I would expect them to be solid products based on the manufacturers reputations in the industrial world.

Phil
 
pso said:
Mitch

Go and read M Spangler's thread about Rotary Phase Converters for an explanation.

http://www.bladeforums.com/forums/showthread.php?t=513096

Here are a bunch of 3 hp VFDs, some with single-phase inputs. The more expensive ones have control schemes built into the software that you probably will never use.
http://www.driveswarehouse.com/show...Horsepower=3.00&IVoltage=&OCurrent=&x=16&y=12

Otherwise, get a VFD rated for at least 5 hp, with a 3-phase input, to run your 3 hp motor. Set the current limit levels on the VFD to the motors nameplate current. They have ratings that are 67% higher than the 3 hp VFDs but only cost about 20% more.
http://www.driveswarehouse.com/show...&Horsepower=5.00&IVoltage=&OCurrent=&x=20&y=6

I have no direct experience with the Hitachi and LG brand VFD's sold by driveswarehouse but I would expect them to be solid products based on the manufacturers reputations in the industrial world.

Phil
Click to expand...

Hey Phil, Thanks for the reply. That is exactly the problem that I was having while searching for a 5 HP compatible VFD.....Most, if not all, require a 3 phase input.::grumpy:
- Mitch
 
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