Should I Use A Rotary Or Static Phase Converter??

   / Should I Use A Rotary Or Static Phase Converter?? #1  

PineRidge

Super Member
Joined
Oct 8, 2003
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Location
Northeast, Ohio
Tractor
LS-MT242HC
My latest eBay acquisition is a hefty 8500 pound South Bend 17" Turn-ado lathe formerly used in a school shop, that I was lucky enough to pick up for $0.06 a pound. Yeah I know even scrap metal is going for more these days..... /forums/images/graemlins/grin.gif

Naturally a lathe this large uses a 3 phase motor and herein lies my question. When it comes to a 5 HP motor will I be better off going to a rotary or a static phase converter for my power needs?

Keep in mind that this lathe will not be used for production so it's highly unlikely that I'll ever come even remotely close to needing the umph that the 5 HP is capable of delivering.
 
   / Should I Use A Rotary Or Static Phase Converter?? #2  
Keeping in mind that I have never had to use either due to having 3-phase power on site, a friend of mine uses a rotary on his metal lathe. He was recommended to get the rotary because of power considerations with a static. Supposedly a static converter only supplies 2/3 of rated motor horsepower.
 
   / Should I Use A Rotary Or Static Phase Converter?? #3  
If cost is the issue, buy a good static converter and connect it to a spare 3-ph motor of the same or larger size as the lathe motor. This combo is then a rotary converter, and it cost you half of what they sell for. You will appreciate the increased power and if you work the motor hard, it will last longer on rotary-produced 3-ph. I am still limping along on a static converter, but keep looking for a spare 3 ph motor to add as a my rotary converter.
 
   / Should I Use A Rotary Or Static Phase Converter??
  • Thread Starter
#4  
Can I ask what one should expect to pay for a good static converter? I know the rotary's are available here for a decent price, and they charge a flat 80 bucks to ship one.

Guess at this point it's a matter of choice. I could easily get away with decreased HP from the motor since I really won't need the full 5HP anyway. Yet if the rotary makes the motor more efficient to run money wise and it's less likely to burn up an expensive 3 phase motor then I'm inclined to go rotary.
 
   / Should I Use A Rotary Or Static Phase Converter?? #5  
You also have the option of using a Variable Speed Drive(VFD) This will give soft start, variable speed, and reversing capability. I have put VFD's on my drill press and wood lathe.
 
   / Should I Use A Rotary Or Static Phase Converter?? #6  
PineRidge,
That link is where I bought mine from. They were the best price and service I could find. Go with the rotary set-up. I've had the static phase converters and they are not that good. You don't get all the hp from your machine. Another thing, you can't reverse the motor...it will keep spinning in the same direction with a static one. Another thing is the start. Some static ones will not start your lathe when in high gear or backgear.

I know this because I've had different machinery in my garage for 30 years. I now have a 16" lathe, 2 milling machines, a surface grinder and a large Lincoln TIG welder. I can run them all on a 10hp rotary converter. You will need to check with them on the size you need. Probably 10hp for your lathe. Maybe 7hp if it will start the motor.

Definitely go with the rotary. I's more expensive but you'll get more use out of your "new" lathe and be able to use it's capacity better.
 
   / Should I Use A Rotary Or Static Phase Converter??
  • Thread Starter
#7  
Rob since you already have a rotary converter can you tell me the idea behind the soft start? Is this a feature to keep starting amps at a minimum so as not to drastically swing a electric demand meter so the electric bill doesn't go sky-high?
 
   / Should I Use A Rotary Or Static Phase Converter?? #8  
Wish I could help you Mike, but i'm not sure what's behind it. When I called American Rotary, they were very informative. I think they have an 800 number. Give them a call and ask them. They'll give you the straight skinny on it.

I do know they rate machinery by easy start...medium and hard start. Your lathe is a hard start and they recommend a 2 to 1 ratio for the size motor of the rotary converter. So your 5 hp lathe needs 10hp converter for the start only.
 
   / Should I Use A Rotary Or Static Phase Converter?? #9  
Pardon my ignorance here...But I have a question to ask...

I am quite competent on 1PH AC and DC electrical circuits, but have zero knowledge of 3PH stuff.

So here is my stupid question. Would it not be easier and cheaper to just get a new 1PH motor, rather than buying a phase converter?

Mike, Do you ever sleep?
 
   / Should I Use A Rotary Or Static Phase Converter??
  • Thread Starter
#10  
<font color="blue"> Pardon my ignorance here...But I have a question to ask...

I am quite competent on 1PH AC and DC electrical circuits, but have zero knowledge of 3PH stuff.

So here is my stupid question. Would it not be easier and cheaper to just get a new 1PH motor, rather than buying a phase converter?


Mike, Do you ever sleep? </font>

Kenny you need to factor in the running amps or the cost of running a 220v single phase compared to a 220 volt 3 phase motor. Not only will the motor be more efficient in running but a lot cheaper overall to run.

5 HP motors aren't cheap to purchase new or used.

One neat thing about 3 phase motors is that you can reverse any two of the three hot wires suppling it with power and it will reverse rotation of the motor.

And yes, I do sleep, with one eye open. /forums/images/graemlins/wink.gif
 

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