Phase Converters

   / Phase Converters #31  
Several years ago when I was looking for a VFD I didn't see many VFDs with a single phase rating once you get over 2 HP. Maybe that has changed.
Yeh, that was one of my issues not going with a vfd at the time, I got a 5hp lathe.
 
   / Phase Converters #32  
Rotary or static converters are an obsolete design from an era where there wasn稚 much else for choice . Now a 10HP VFD on a 5HP motor is the answer.
 
   / Phase Converters #33  
A three phase VFD supplied with single phase can only produce 57.7% of it’s nameplate capacity .
Constant pressure well pumps are a common use of a VFD to convert single phase into variable frequency three phase .
 
   / Phase Converters #34  
Rotary or static converters are an obsolete design from an era where there wasn稚 much else for choice . Now a 10HP VFD on a 5HP motor is the answer.

Cool. Technology marches on.
 
   / Phase Converters
  • Thread Starter
#35  
Out of curiosity; what does a VFD that will drive a 10 HP 3 phase motor and be fed with a single phase circuit cost? I did not even know such an animal exists. VFDs to drive 3 phase motors with a 3 phase input were still becoming popular when I left the mechanical trades. Single phase to single phase was also available for small motors but not economical by any means. In my day when a 3 phase motor had to used on a single phase supply e used an open delta transformer connection. Same problem of loss as you all are discussing in this thread, just oversize the transformers and the primary circuit to match the load with the loss. Inspectors required that we well identify and have a warning label about the "wild leg" which was more than double the phase to ground voltage. You talk open delta to electricians today and they give you a blank look.

Most people do not know that a 3 phase motor will continue to run if one of the 3 legs drops out while running albeit kinda overheats. Do not try to start though. I once worked around a gippo sawmill outfit that used over size 3 phase motors for their loads (cheap on the used market) and they had a small single phase motor rigged to bring the big motor up to operating speed, unloaded, and then the switched on the 3 phase motor, then clutched in the load Burn up a motor, just go get another used one. Amazing what we ran into back in the 50s an 60s. Smaller cities did not have 3 phase power except in industrial areas.

After WWll, all of a sudden folks wanted air-conditioning. Any single phase motor over 5 HP was rare and expensive compared to 3 phase. Power companies did the open delta thing for years till distribution lines caught up. Then even 2HP and up became cheaper and more available in 3 phase. Hermetic motors then brought us a whole new set of problems. Back in those days a Refrigeration Tech had to be good electrician too.

Some day, when I feel like it, I will relate how we powered hermetic compressors for refrigerated trucks using 2 phase alternators driven off the engine and primitive speed/frequency control.

Ron
 
   / Phase Converters #36  
While on the topic, once I get my shop built I have a 3hp 3 phase 440V mill that I got cheap, my house doesn't have 3 phase... I will be getting a panel set up for the shop but I don't think 3 phase is doable, it is only a 100' run from the power pole though...

Anyone know of any options to get a VFD from single phase 220 to 440V 3 phase?
 
   / Phase Converters #37  
VFD's are cheap and give you a lot of features. The only option IMHO. But I work on them for a living so my opinion is skewed. I would go with an ABB personally. Allenbradly makes some single phase specific VFD's designed for just single phase input.

Something like a drill press it is really nice because you can get away from pully swapping for speed changes and just change the speed on the drive.
 
   / Phase Converters #38  
I bought VFDs used on Craigslist. Paid around $300 for a pair of them with breakers. Be careful buying old ones though, the capacitors can go bad if they sit unused for a long time. I ran them unloaded for a few days after wiring them up. IMG_20160204_234712.jpg
 
   / Phase Converters #39  
Out of curiosity; what does a VFD that will drive a 10 HP 3 phase motor and be fed with a single phase circuit cost? I did not even know such an animal exists.

Evidently they do and they're ridiculously cheap.
 
   / Phase Converters #40  
Out of curiosity; what does a VFD that will drive a 10 HP 3 phase motor and be fed with a single phase circuit cost? I did not even know such an animal exists.
The tend to cost about $125 to $150 per hp. Here's a website with several different sizes available from 1 hp to 30 hp. phase converter drives
 
 
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