How can I convert a three phase to single

[Pa19331247]

My neighbor offered my nice three phase ten horse air screw compressor for under a thousand bucks. The thing is spotless, however I don't know how many hours are on it. I only have 60 amps and single phase 220. Is there a reasonable way to convert it. Would a 10 horse single phase work. Thanks D

 

[Spyider]

get a converter or a new motor.. im in the same boat as you right now but i bought it as it was too good a deal to not..

 

[bczygan]

Rpc...............

 

[Charles (in GA)]

Not sure of the power that a RPC large enough to run a 10 hp 3 ph compressor would require, but its almost certainly more than the OP has available, and unless the OP has a real use for it, probably should let the idea pass.

 

[CNGsaves]

What country are you in ??? Update GJ Profile with City/State/Country.

What is CFM of the 10 HP screw compressor ?? How can you possibly use even a fraction of that capability ?? What will you use it for ??

Better solution is buy compressor for $1K and thank him. Then after researching best places to sell, cash in on $3K to $5K value and SELL it.

Then buy yourself a 60 gal 5 HP 2 stage compressor that will run in your garage and any airline system of copper or black pipe steel you want to install !!

 

[macgyver37]

10 hp single phase will work just fine, finding one that you can afford will be the issue, it will also need alot of juice to kick it on at start, may be over your 60 amp capacity.

Now that I think about it, look into the controls closely to make sure that they aren't 3 phase as well, the screw compressors will typically go into a standby mode when up to pressure, so the controls etc may be 3 phase, or you might get lucky and they have a transformer in there and it is 24v. Just have to look.

 

[zkling]

Most screw units have hour meters.
Phase conversion on a compressor is one of the most difficult machines to convert, especially on a reciprocating unit. Ideally a single phase motor would be the way to go, but that can get very expensive. A large rotary phase converter can work.

I'd seriously ask myself if it is really worth the hassle/expense. Do I really need the air output and is the rest of the unit in good enough condition to put the time and money in on. Should be in the ~40CFM @90psi neighborhood.

 

[930dreamer]

When testing a 10hp three phase compressor setup a while back, I believe the inrush current was over 200 amps. This was done on true off the pole three phase power.

 

[justanengineer]

Cant say Ive ever worked on a screw compressor but my first thought would be to simply swap the motor to a single phase motor.

 

[Dagny]

pretty much would use up your entire electric supply.

 

[James-W]

I think the best idea is to go with the "buy it and then sell it" plan. It is a lot of compressor and unless you have a need for it I doubt it is worth the cost to get it running in your shop.

 

[A_Pmech]

I was all for it until I read "60 amp service."

That's cutting it a little tight!

 

[jeff000]

When testing a 10hp three phase compressor setup a while back, I believe the inrush current was over 200 amps. This was done on true off the pole three phase power.

This. Even spending 600+ on a 10hp single phase motor your service will never hold it.
And what could you possibly need that much air for?

 

[sberry]

This is not for you.

 

[banditbigdog]

The screw compressors I've had experience with were all direct drive and the motors were made specific to that application when it comes to the output shaft and flange mounting.

If this is the case finding a drop in single phase motor with the exact
same mounting dimensions (output shaft profile / shaft dia. /shaft length / mounting flange) could be tricky.

 

[BigNuge]

What country are you in ??? Update GJ Profile with City/State/Country.

What is CFM of the 10 HP screw compressor ?? How can you possibly use even a fraction of that capability ?? What will you use it for ??

Better solution is buy compressor for $1K and thank him. Then after researching best places to sell, cash in on $3K to $5K value and SELL it.

Then buy yourself a 60 gal 5 HP 2 stage compressor that will run in your garage and any airline system of copper or black pipe steel you want to install !!

^^This^^

I am in the Commercial/Industrial boiler business. I deal with motors of that size and bigger all of the time. I also deal with phase inducers (which is what you'd need) all the time. This is just far too much compressor to try and operate on a single phase residential service. I'm setting up to run a 7.5 HP @ 240 on a 60 amp service, and thats tight. 10 HP....no way.

Buy it, make sure its nice and clean, then sell it. You'll have to get it marketed right, but you'll have plenty of $$ to buy the right size machine.

 

[Stuart in MN]

For a motor that large, besides having to deal with your 60 amp service and the three phase conversion issue, you should also check with your local electric utility - they may or may not be interested in providing power for a non-commercial application like that. I was just looking at the handbook for my local power company (Xcel Energy, in the upper Midwest) yesterday and read this section:

6.4.5. Horsepower Rating
Motors rated 5 horsepower or smaller shall be single-phase unless an established three-phase service exists. Single-phase motors larger than 5 horsepower will not be permitted on services supplied on a residential rate schedule without permission of the Company. Single-phase motors larger than 5 horsepower may be permitted on services supplied on a non-residential rate schedule with Company approval. Larger motors may require starting compensation to limit voltage variation on the system - consult the Company if there is any doubt. The Company will not be held responsible for, nor continue service to, motors with unacceptable starting characteristics.

Different utilities have different regulations, so this is just an example. You need to confirm how they do things in your area.​

 

[theoldwizard1]

Buy a 5hp single phase motor and change the pulley size.

You should be able to sell the 10hp 3 phase motor and make $$$.

 

[930dreamer]

Without being able to power the compressor, selling it might be a problem.

 

[Thumper68]

I would pass on this one, just to much trouble for not enough gain. I passed on a very clean newer dual motor, dual pump commercial 3 phase compressor at an auction a few months ago I could have gotten it for less than $100 but without 3 phase power and a real need for that much compressor it was not worth it to me, even to maybe find a buyer that was willing to take a chance on a used unit that they could not hear/see run.

 

[justanengineer]

JMO but I'm not seeing what the big deal is. The OP said it was an industrial unit not phony Chinese power, 60 amps should handle the compressor fine either re-motored or via a VFD ($$$ unless used) and I wouldnt expect much in the way of a starting surge with a quality compressor connected. If for some reason the inrush current starts tripping breakers a programmed (VFD) soft start or soft starter would take care of it. Granted, I wouldnt expect more than ~10 amps excess with the compressor running, but in a hobby shop that could be overcome by either adjusting the pressure switch or by simply turning the compressor off when not needed.

If it was my shop, I wanted to be overkill on air, and had excess money Id buy it, but I have 60 amps @ 220V on a dedicated line as well as two separate circuits for 110V @ 20, one for lights and the other outlets. I also live in the midwest and can get 10 hp single phase motors for ~$100 used from several sources given a week or so.

 

[jeff000]

JMO but I'm not seeing what the big deal is. The OP said it was an industrial unit not phony Chinese power, 60 amps should handle the compressor fine either re-motored or via a VFD ($$$ unless used) and I wouldnt expect much in the way of a starting surge with a quality compressor connected. If for some reason the inrush current starts tripping breakers a programmed (VFD) soft start or soft starter would take care of it. Granted, I wouldnt expect more than ~10 amps excess with the compressor running, but in a hobby shop that could be overcome by either adjusting the pressure switch or by simply turning the compressor off when not needed.

If it was my shop, I wanted to be overkill on air, and had excess money Id buy it, but I have 60 amps @ 220V on a dedicated line as well as two separate circuits for 110V @ 20, one for lights and the other outlets. I also live in the midwest and can get 10 hp single phase motors for ~$100 used from several sources given a week or so.

A 10hp 230v motor will draw 41 amps at full load. Starting I would expect at least 150 amps.
You are going to need to have a motor rated for the same RPM, I've never seen a 10hp for 100$ they are worth more as scrap. Expect 600+.

A VFD for phase conversion is going to run 800+ for a 20hp unit.
It's still going to be a 25a draw on a 60a service.

He could buy it and try and resell, but may end up trying to pawn it off to a neighbor when he can't sell it for what he thinks it's worth.

 

[A_Pmech]

JMO but I'm not seeing what the big deal is.

If he soft starts it with a VFD, he could probably get by on the 60A service if that's all he's going to run besides some lights.

I doubt a 60A breaker would hold for an across-the-line start on single-phase though. It might work with a rotary phase converter as the converter moderates the inrush current, but that's an "if".

I got by running 10+ HP machines on a 50A service though a rotary converter until I could afford to upgrade (and now I need to upgrade again), but I had the breakers on the pole pegged closed with bits of dowel rod.

 

[Pa19331247]

Thanks again guys, I think you have all convinced me to let this one go. It was tempting to have all the air i could ever hope for, but it looks like far to much trouble and expence. I will see if a 7 1/2 hp single phase will work. Thanks. D.

 

[sberry]

How can I convert a three phase to single

I like these questions, you always get some good answers. A more appropriate question would be,,, is all this a good idea for me? Buy sell equipment you are not familiar with, cant use, need complicated conversion and additional layer of wiring, change a motor on a unit too big for my service etc and etc.
I can and don't how is that. I got a live in tech can build any kind of watt or ohms I want and still have it all I can run from 50A service, most things 30.
I do have 400 and do have a 300 synch but I don't use it so it really don't count as I use a buzz box and 30A wire feed.
I live rural and just font happen to have 3 ph, I may have got machine tools if I had it. In the end I really don't want to do that anyway and maintenance has changed dramatically in 30 yrs. Its rare I got to run down to neighbors for actual machine work. Used to be so much equipment was built that way, not so much today.
We resemble more of a racing crew than machine shop in nature as ours isn't heavy equip type but more specialized or tuned to be lighter. I can haul my largest tractor on a single axle flatbed.
50A welding service is adequate. Find pieces you can run from that max that take the same 3 wire cord in life and make it easy. No matter how good this deal let him sell to someone that wants or needs it before you got something you got a grand in to and even if you were Edisons nephew is gonna go another 1K somehow with free parts to end up making air you could have got the need for fulfilled for 500$ new in box to a common circuit with a common wire.

 

[sberry]

Asking how to do is one thing,,, what you may need and is practical is another. Just like asking whats the best?

 

[sberry]

That comp is ideal for an addition to a multi man body shop. It is not for a home shop, its not for a hobby shop, its not even good for a small body shop. It is cheap enough it could be dedicated to sandblast if you needed it but not great for standby air.
Again subject to practical need and power from poco ideally.

 

[BigNuge]

I like these questions, you always get some good answers. A more appropriate question would be,,, is all this a good idea for me? Buy sell equipment you are not familiar with, cant use, need complicated conversion and additional layer of wiring, change a motor on a unit too big for my service etc and etc.

I can and don't how is that. I got a live in tech can build any kind of watt or ohms I want and still have it all I can run from 50A service, most things 30.

I do have 400 and do have a 300 synch but I don't use it so it really don't count as I use a buzz box and 30A wire feed.

I live rural and just font happen to have 3 ph, I may have got machine tools if I had it. In the end I really don't want to do that anyway and maintenance has changed dramatically in 30 yrs. Its rare I got to run down to neighbors for actual machine work. Used to be so much equipment was built that way, not so much today.

We resemble more of a racing crew than machine shop in nature as ours isn't heavy equip type but more specialized or tuned to be lighter. I can haul my largest tractor on a single axle flatbed.

50A welding service is adequate. Find pieces you can run from that max that take the same 3 wire cord in life and make it easy. No matter how good this deal let him sell to someone that wants or needs it before you got something you got a grand in to and even if you were Edisons nephew is gonna go another 1K somehow with free parts to end up making air you could have got the need for fulfilled for 500$ new in box to a common circuit with a common wire.

??what??

That is the most confusing read ever....lol


Sent from Taptalk

 

[gorilla]

I bought a 10HP rotary phase converter for my shop almost 20 years ago. It cost about $1700.00 I think you could buy a nice air compressor for less than the cost of a RPC.

 

[wyliesdiesels]

Id be surprised if a 60a breaker would hold with a 10hp motor starting across the line.

Typically the breaker would be in the 100a range for a motor that size...

The wire for that motor would have to be #6 THHN or #4 NM-b.

If the OP had anything else running at the same he would be chapped!!

60a is really not enough for that since continous loads are sized @ 125% which would be 62.5a for a 10hp motor.

Honestly its not worth the hassel for a small shop...

??what??

That is the most confusing read ever....lol


Sent from Taptalk

Thats how sberry rolls. I think his english is a little poor, but he does know what he is talking about for the most part and has the experience.

Over time u learn how to read his posts...

 

[sberry]

??what??

That is the most confusing read ever....lol


Sent from Taptalk

Yeah, the point is as a couple others have made is that they could have nice plug and play for a reasonable cost.

 

[LS6 Tommy]

You're looking at somewhere between $1-2k just for a motor IF you can match the NEMA frame size...

Tommy

 

[930dreamer]

Any pics of the compressor?

 

[Alan Douglas]

That is the most confusing read ever....lol

Not really. Reminds me of the quote attributed to Pascal: I apologize for this long letter; I didn't have time to write a shorter one.

 

[sberry]

Its no worse than taking 20 responses to a question to find out that this is some speculative good deal scheme involving a neighbor for an item I cant even use.

 

[sberry]

The first response to the op should have been a question,, why you want to do this?

 

[Ross/Kzoo]

6.4.5. Horsepower Rating
Motors rated 5 horsepower or smaller shall be single-phase unless an established three-phase service exists. Single-phase motors larger than 5 horsepower will not be permitted on services supplied on a residential rate schedule without permission of the Company. Single-phase motors larger than 5 horsepower may be permitted on services supplied on a non-residential rate schedule with Company approval. Larger motors may require starting compensation to limit voltage variation on the system - consult the Company if there is any doubt. The Company will not be held responsible for, nor continue service to, motors with unacceptable starting characteristics.

Different utilities have different regulations, so this is just an example. You need to confirm how they do things in your area.​

Stuart has it nailed pretty well. I worked in the engineering dept at the power co for 40+ years and ran across this occasionally. In a residential area if you have a load that noticeable/objectionable to the neighbor you would need to pay to isolate your load. could be $400 to thousands of dollars. Also the 80% rule holds for your 60 amp service, 60 amps x 80%= 48 amps of continuous load.

 

[sberry]

I use a 3 hp on air and do have a backup of 5 and a lot of tank on but the 3 is really kind to the electric system and is my primary. I can barely tell it starts. I am probably the only motor load over 3/4 hp on 4 miles of line.
I have 400A service equipment, new ****** but small and a 5 will flicker lites as to notice on a compressor.