VFD help!

T

The Fool

Joined
Feb 3, 2004
Messages
3
Hi everyone,

I've been looking for a variable speed AC motor setup to power a KMG that I'm planning on ordering. I found a used Baldor Industrial 3 HP, 3 phase motor for cheap.

However, when I called a local company to ask about VFD's, they said that since I would run the vfd off of a single phase, 220V source, I would actually need a VFD that was rated for double the horsepower, 7.5 HP, and that would cost me over $700. They also said if I had a single phase motor, then I could use a VFD rated for 3 HP, but definitely not for a 3 phase motor.

Is this true? I was searching through old threads on Bladeforums about this subject and nowhere could I find anything that said I needed a VFD rated to twice the HP. If so it seems like all you guys with 3 HP motors would be spending obscene amounts of money on VFD's.

Also, I was wondering what manufacturer makes the best quality VFD, I've found a couple new rated for 3 HP from Hitachi, Leeson, Teco, and LG for around $280. I would probably get the Leeson since I like to buy from US companies. And, is this a good price? If not, where can I get them cheaper? I've checked dealerselectric.com, e-motorsonline.com, and driveswarehouse.com.

Thanks,
Robert
 
I looked at dealer's electric, but I don't want the complete package - only the drive - since I already have the motor.
 
Hello Robert

Here's my 2c worth from the perspective of someone who has not used VFD's with any knifemaking equipment but has designed VFD's at a company that manufactures VFD's. I have been doing all my work with files and sandpaper.

The prices that I have seen at Dealer's are pretty good. I am sure that they will sell you just the VFD.

I had posted a (non-exhaustive) survey of different VFD's available back in Oct. 2002 where I show which product families will work from single-phase 220V supplies:

http://www.bladeforums.com/forums/showthread.php?t=222749

You may also try contacting some manufacturers of VFD's, directly, to see if they have refurbished units. I know that Toshiba sells some of them for about $200. They probably have a "reduced" warranty and they should come with a manual.

I believe that Ron Frink, maker of the KMG also sells VFD's and motors.

I also posted some safety precautions and some comments relating to potential problems with your motor in the following thread:

http://www.bladeforums.com/forums/showthread.php?t=221286

It is great that you want to "buy American". Unfortunately, it may be difficult to know if the VFD that you are buying was really made in the US since many of the manufacturers have operations all over the world and certain product ranges may be produced only in one plant, say in Germany. Toshiba VFD's sold in the US and some of the Schneider (Square-D) models are made in Houston Texas. I think that TB Woods and Allen Bradley are based in the US but I don't know where their manufacturing is done. Many of the makes/models are "private labelled" and are really manufactured in plants in Taiwan and China (quality is still OK) or are the result of some joint venture (GE & Fuji).

For the best quality, go with the bigger and more recognizable names. The intended market for VFD's are industrial plants. Reliability and low cost are the two main selling points. The ones that you mention are probably all OK, though I have never heard of Teco.

Sorry for the long post. Just unwinding after helping count inventory here at work.

Phil
 
I was going to recommend that you look at the Phase Converters & VFD forum over at www.practicalmachinist.com, but then I read phil's thread and It seems to answer a few questions I've had as I've been considering a VFD for my Bridgeport mill.

Thanks Phil

John
 
Robert

Oh yes, I forgot. It is true that you will have to use a VFD with a rating that is 1.5 to 2 times greater than the rating of your motor if you are going to use it with a single-phase supply. The design of the VFD's is typically optimized for operation from a three-phase supply. To operate from a single-phase supply, some components (input rectifiers and DC-bus capacitors) would have to be larger (by about 1.5 to 2 times) and hence more expensive. I would suggest contacting the manufacturer's directly and ask to speak with an Applications Engineer. They should have extensive knowlege about their products and should be able to help you select an appropriate model. You may find that many of the distributors and re-sellers are not that well educated about VFD's, since they probably also sell all kinds of other equipment, and may not have much experience with VFD's running from single-phase supplies. You may still have to buy your VFD from a distributor, but you can then give them the exact model number and be confident that it will work for you.


John

I think that you will enjoy using a VFD on a milling machine. I used a drill press with one and it was really nice. Continuously variable speed, smooth start up and instant stop. You are probably best off to spend a bit more and get one with an alpha-numeric display that shows the motor's rpm so that you can do things more repeatably on your mill.
 
Phil,

Thanks for all the advice.

After checking the Dealer's Electric drives, I noticed they say that the 1-3 HP Teco-Westinghouse FM 100 VFD they sell is rated for full HP running off of 220V single phase. I'll probably go with them if that is the case - I don't want to risk buying a derated drive.
 
Robert

Derating a drive means to use it at less than rated capacity. The drive is not physically altered to be different or inferior to the original. You will just be paying more for a 7hp (nominal) drive to use with a 3hp load than if you could use a 3hp (nominal) load. Many pieces of equipment are derated for reasons such as altitude, ambient temperature and supply voltage.

The price for the single-phase rated Teco-Westinghouse FM100-203-N1 looks pretty good. The beefier components needed to allow it to do this are probably only worth about $20-30 but that is probably a large portion of the manufacturer's profit.

Phil
 
I'm not sure how I got to this thread & PSO's other thread (very informative post). It's very good reading. I got to the industry in 2007. I have seen lot of changes in VFDs in 3 years. There are lot of choices now. The prices seem to have gone down even further. Like Phil mentioned one cannot really pinpoint if a VFD is made in a particular country. It seems like everybody is private labeling for somebody else. The cheapest made in USA (not really sure) drives that I know of are made by AC Tech in Massachusetts. I know for sure they private label for Leeson.

I'm sorry that I posted on this thread. I didn't mean to resurrect a 6 year old thread. It was very interesting to read posts by Phil.
 
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No, you do NOT have to use a VFD rated higher than the motor, if the VFD is designed for single-phase input.

Dealers Electric and Automation Direct both sell single-phase VFDs- if you have a 2HP 3~ motor, buy a 2HP VFD that takes 220V 1~ input. Easy as that.

The confusion comes from the fact you can, in most cases, use a 3-phase input VFD with single phase in. Some people do this because you can find 3Ph-in VFDs for somewhat cheaper than single-phase ones, and sometimes a good deal makes it worth it.

In that case, yes, you have to derate the VFD by half. If you have a 2HP motor, you'd need a 5HP VFD. (Only because they don't make a 4HP VFD.)

But again, if you're buying new, buy a VFD designed to take single phase in, for the motor's rated HP, and call it good.

Doc.
 
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