# 2 phase motor on 3 phase



## hydro (Aug 21, 2009)

Hey boys, buddy of mine is looking at buying a jointer from an auction that has a 2 phase 5 hp motor. I know nothing about 2 phase aside from what I've read here. His shop has a single phase service and a homemade RPC for his 3 phase power. Is there anyway to run a 2 phase motor on either one of those supplies. Changing the motor isn't an option. I suppose it could be rewound if necessary. Thanks guys.


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## erics37 (May 7, 2009)

A 2-phase motor?

How old is this thing?

Are you sure?


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## hydro (Aug 21, 2009)

I thought the same thing but ya I looked at the auction listing and they made a note of it specifically. If say the machine is from the 40's. plus it's out of Pennsylvania where as I understand it they still use 2 phase systems in older buildings.


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## oldtimer (Jun 10, 2010)

hydro said:


> Hey boys, buddy of mine is looking at buying a jointer from an auction that has a 2 phase 5 hp motor. I know nothing about 2 phase aside from what I've read here. His shop has a single phase service and a homemade RPC for his 3 phase power. Is there anyway to run a 2 phase motor on either one of those supplies. Changing the motor isn't an option. I suppose it could be rewound if necessary. Thanks guys.



2 phase ? --- 2 hots , no neutral ? :001_huh:

Please explain . 

What voltage ?


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## erics37 (May 7, 2009)

hydro said:


> I thought the same thing but ya I looked at the auction listing and they made a note of it specifically. If say the machine is from the 40's. plus it's out of Pennsylvania where as I understand it they still use 2 phase systems in older buildings.


Well if that's the case I think there's a way to rig up transformers to get 2-phase out of 3-phase, but I don't think it'd work for single-phase. I don't have the foggiest idea how to do that anyway.

Why is putting in a different motor not an option?


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## hydro (Aug 21, 2009)

oldtimer said:


> 2 phase ? --- 2 hots , no neutral ? :001_huh:
> 
> Please explain .
> 
> What voltage ?


From what I understand its 4 hots sorta like a double polyphase system.


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## hydro (Aug 21, 2009)

erics37 said:


> Well if that's the case I think there's a way to rig up transformers to get 2-phase out of 3-phase, but I don't think it'd work for single-phase. I don't have the foggiest idea how to do that anyway.
> 
> Why is putting in a different motor not an option?


Ya I saw something called the "Scott system" trying to understand how I can make this work without a custom made transformer. 3 phase is available off the RPC. 

In the case of a different motor. The motor is a custom motor built right into the machine. Plus I would imagine its a high speed motor as its direct drive right to the cutter head and those cutter heads need to turn at around 5500 rpm


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## bkmichael65 (Mar 25, 2013)

oldtimer said:


> 2 phase ? --- 2 hots , no neutral ? :001_huh:
> 
> Please explain .
> 
> What voltage ?


4 hots, 2 phases 90 degrees apart


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## hydro (Aug 21, 2009)

bkmichael65 said:


> 4 hots, 2 phases 90 degrees apart


Any idea how to run that on 3 phase haha


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## Peewee0413 (Oct 18, 2012)

???????? Lol


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## Big John (May 23, 2010)

Like the other guys said, you need a Scott connection transformer. It has four windings: Two high windings that are "T" connected that you would hook your 3Ø up to, and two independent low windings that are 90° out of phase with each other. 

If this really is a 2Ø motor you'd hook it up to the 4 wire low side and it would work.

I've never had to gang a Scott connection, but thinking out loud here, it *might *be possible to build one out of a couple of single-phase transformers that had center winding taps and it could save you some money over buying one. Someone will have to double check me on that.

But personally, I'd just buy a new 3Ø 5HP motor.


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## bkmichael65 (Mar 25, 2013)

hydro said:


> Any idea how to run that on 3 phase haha


2 phase generator/phase converter?


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## Peewee0413 (Oct 18, 2012)

They sure do make em...actually Google the question and u see converters pop up...


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## Vintage Sounds (Oct 23, 2009)

Rather than convert from single phase, to three phase, and back to two phase, it seems like changing to a new, single phase 240v 5hp motor would be the simplest, most reliable and most energy efficient option if you could get it to physically fit.


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## hydro (Aug 21, 2009)

Vintage Sounds said:


> Rather than convert from single phase, to three phase, and back to two phase, it seems like changing to a new, single phase 240v 5hp motor would be the simplest, most reliable and most energy efficient option if you could get it to physically fit.


That's not an option


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## Peewee0413 (Oct 18, 2012)

Cause the motor is built inside? Don't understand how something is built with a motor that is inaccessible.


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## hydro (Aug 21, 2009)

Because its a custom mount designed for that specific machine and it's a high speed motor


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## wildleg (Apr 12, 2009)

sounds to me like a waste of money buying an outdated jointer. what about bits for the damned thing ? 

anyhow, here's a post from another forum.

http://www.practicalmachinist.com/vb/transformers-phase-converters-vfd/single-phase-two-phase-three-phase-158678/


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## Peewee0413 (Oct 18, 2012)

Pay to convert 3phase to 2 phase. .or sell it...


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## hydro (Aug 21, 2009)

Peewee0413 said:


> Pay to convert 3phase to 2 phase. .or sell it...


What are you talking about


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## oldtimer (Jun 10, 2010)

I would really like to learn more about 2 phase power ... ... What are the advantages or disadvantages ?

I must admit I know absolutely nothing about 2 phase power !

I have seen machines that have built in motors that are made specifically for that machine , and some that are impossible to replace.
I had a problem with a machine made for sharpening industrial saw blades . It was made in Italy . It was an older machine , and I do not know what happened to it , after I tried unsuccessfully to find a replacement motor .
I told the owner to try to get the motor rewired , but I do not know if he ever did.

Sometimes when people buy this equipment , they think they are getting a real good deal , but then repairs are not feasible !


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## Peewee0413 (Oct 18, 2012)

Pretty much 2 phase old and 3 phase new...??????


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## Big John (May 23, 2010)

oldtimer said:


> I would really like to learn more about 2 phase power ... ... What are the advantages or disadvantages...?


 Two phase was developed because you don't need starting capacitors to spin motors like you do with single phase: Just like three phase, it produces differing currents in the windings so that there's an attractive magnetic field that spins the rotor.

I don't know the history, but I assume that 2Ø was just discovered or made practical before 3Ø and that's why it was widely used for a while.

The disadvantage is that it takes as much copper to transmit 2Ø as single phase because you're supplying the loads with two completely independent circuits that required two conductors each, so 3Ø uses 25% less copper.


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## JRaef (Mar 23, 2009)

Big John said:


> Two phase was developed because you don't need starting capacitors to spin motors like you do with single phase: Just like three phase, it produces differing currents in the windings so that there's an attractive magnetic field that spins the rotor.
> 
> I don't know the history, but I assume that 2Ø was just discovered or made practical before 3Ø and that's why it was widely used for a while.
> 
> The disadvantage is that it takes as much copper to transmit 2Ø as single phase because you're supplying the loads with two completely independent circuits that required two conductors each, so 3Ø uses 25% less copper.


That's all pretty much correct from what I know too. Tesla's first "polyphase" motors and transformers were 2 phase, but the Europeans were already using 3 phase for transmission, so eventually the logic of getting more power with less copper took over.


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## just the cowboy (Sep 4, 2013)

I worked with an oldtime navy guy, and he said give me a bunch of single phase xformers and I'll get you any power you want, so I guess it can be done. When I was in High school in Indrustial Electric class my teacher got a lot of old 2 phase stuff for us to work on because the factories were switching over to 3 phase.


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