Phase Converter

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jerjwillelec

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Nevada, IA
I haven't ever dealt with phase converters and would value everyone's wisdom and opinions. I need to provide power to a piece of (wood working) equipment 230 volt 3 phase 10 HP and we only have 120/240 volt 1 phase available. He is a smaller shop so not looking for top of the line equipment. What brand and model would you recommend? Anything out of the ordinary I would need to know sizing this?

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ActionDave

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I haven't ever dealt with phase converters and would value everyone's wisdom and opinions. I need to provide power to a piece of (wood working) equipment 230 volt 3 phase 10 HP and we only have 120/240 volt 1 phase available. He is a smaller shop so not looking for top of the line equipment. What brand and model would you recommend? Anything out of the ordinary I would need to know sizing this?

Sent from my SM-G920R4 using Tapatalk
For a motor that size I would look hard at the cost of a new single phase motor. I bet the cost won't be much higher than a phase converter.

If you simply must convert any rotary phase converter is fine. Don't use a static converter. VFD is another option.

I would swap the motor.
 

yanici

Senior Member
Location
Atlantis
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Check to be sure whether the motor needs to be reversible while in use as part of its normal function, if you're going to change to single phase.
 

iceworm

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EE (Field - as little design as possible)
For a motor that size I would look hard at the cost of a new single phase motor. I bet the cost won't be much higher than a phase converter.

If you simply must convert any rotary phase converter is fine. Don't use a static converter. VFD is another option.

I would swap the motor.
Why not? I'm okay either way. I just don't know much about phase converter applications. (I think) I understand the basic physics of both, but nothing past that. So, why wouldn't one want to use a static converter?

ice
 

ActionDave

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Why not? I'm okay either way. I just don't know much about phase converter applications. (I think) I understand the basic physics of both, but nothing past that. So, why wouldn't one want to use a static converter?

ice
They are basically just a way to get the motor started spinning and the motor runs single phased. They are okay for light duty.
 

iwire

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Location
Massachusetts
10 HP is 10 HP single or thee phase. You just need the same frame. Look on the motor nameplate, somewhere it will say Frame or FR.

Won't a single phase 10 HP be much larger than a 10 HP in three phase?

My point is a single phase motor might not fit in the space of the three phase.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
They are basically just a way to get the motor started spinning and the motor runs single phased. ....
Did not know that. Maybe I don't understand the physics as well as I thought

They are basically just a way to get the motor started spinning and the motor runs single phased. They are okay for light duty.

So the load can not be set up to pull 100% motor rated horsepower? That sounds awkwardly phrased. I'm thinking even a 1.0SF motor, operating on normal 3phase, will stay alive at 100% loading. But you are saying - on a static phase converter, can't get there? If it is operating single phase, so two legs at say 140% FLA and one at near zero? (This is a question - not a statement.) Am I getting it?

ice
 

ActionDave

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Did not know that. Maybe I don't understand the physics as well as I thought



So the load can not be set up to pull 100% motor rated horsepower? That sounds awkwardly phrased. I'm thinking even a 1.0SF motor, operating on normal 3phase, will stay alive at 100% loading. But you are saying - on a static phase converter, can't get there? If it is operating single phase, so two legs at say 140% FLA and one at near zero? (This is a question - not a statement.) Am I getting it?

ice
I'm just a wire pulling grunt. All I know is with a roto phase you are generating a real third phase, with a static you are not.
 

Jraef

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A 3 phase motor will operate (meaning spin) with single phase, but will not START spinning, because there is no relative rotation direction, so it just shakes back and forth, or if it does start turning, the direction is unpredictable.

So a Static Phase Converter (SPC) at it's basic form just uses capacitors to create a phase shift in the beginning that tells the motor to start spinning in your desired direction. Once it IS spinning, then the power capacity is effectively reduced, because all of the work will be done by only 2 sets of windings. So if the motor were to be fully loaded, the current on those windings would increase by the square root of 3, or 173% and the motor would be overloaded. So if you want to use it, you must de-rate the motor by the inverse, to 58% at least, and even then the unbalanced current will cause added heating in the windings by virtue of what's called "negative sequence currents", so further de-rating is necessary. The generally accepted rule is 50% de-rate for things like tools that are not used continuously, but I always tell people if it is going to run for 3 hours or more at a time, de-rate to 33%.

A Rotary Phase Converter (RPC) takes a larger 3 phase motor that is driven by a single phase motor (Pony Motor RPC), or in some cases people use an SPC to start the 3 phase motor of the RPC so it is self contained, and uses the 3 phase motor to "generate" a voltage on the unused leg by induction, thus making it useful to other motors connected down stream. But from an energy standpoint, that second (or 3rd) motor represents energy consumed to create the 3 phase power for the tool motor, so the overall energy efficiency is quite low, in the neighborhood of 60-70%. Again, for a tool running occasionally, that might not be a big deal but for something that needs to run a lot, it adds up fast in terms of cost of ownership. It also means having to start the RPC first, THEN start the tool, every time, or leave the RPC running continuously, which is a total waste of energy.

A VFD works by converting AC to DC, then back into what the motor thinks is AC. So the incoming AC can be single phase or 3 phase, it doesn't matter because it's just rectified to DC anyway. But to feed the VFD with single phase, again that current increases by 1.732, so the front end components need to be larger, plus there is more undesirable bus ripple from rectifying single phase, so you need more capacitance on the bus and the caps will run hotter. So the rule there is at least a 50% de-rate of the VFD, IF you also de-rate the operating temperature by 50%, or if you want rated operating temperature, de-rate the VFD to 35%. So for a 10HP 230V motor, you would buy at least a 20HP VFD if you can keep it at about 20C (68F), or a 30-40HP VFD is you want to use is at up to 40C (104F). If the VFD has DC Bus Chokes you can usually get away with just the 50% de-rate without the temperature de-rate, but of course that means the VFD costs more.

Another alternative is an Electronic Phase Added system that uses the equivalent o a VFD only to create the 3rd leg. They are made by a company called Phase Perfect. That might be a viable option for you here.

I would just replace the motor if it were me...
 

norcal

Senior Member
The only problem with swapping the motor is if it's proprietary, direct drive, or something like that, otherwise it's the simplest solution to go with a single phase motor.
 

ActionDave

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A 3 phase motor will operate (meaning spin) with single phase, but will not START spinning, because there is no relative rotation direction, so it just shakes back and forth, or if it does start turning, the direction is unpredictable.

So a Static Phase Converter (SPC) at it's basic form just uses capacitors to create a phase shift in the beginning that tells the motor to start spinning in your desired direction. Once it IS spinning, then the power capacity is effectively reduced, because all of the work will be done by only 2 sets of windings. So if the motor were to be fully loaded, the current on those windings would increase by the square root of 3, or 173% and the motor would be overloaded. So if you want to use it, you must de-rate the motor by the inverse, to 58% at least, and even then the unbalanced current will cause added heating in the windings by virtue of what's called "negative sequence currents", so further de-rating is necessary. The generally accepted rule is 50% de-rate for things like tools that are not used continuously, but I always tell people if it is going to run for 3 hours or more at a time, de-rate to 33%.

A Rotary Phase Converter (RPC) takes a larger 3 phase motor that is driven by a single phase motor (Pony Motor RPC), or in some cases people use an SPC to start the 3 phase motor of the RPC so it is self contained, and uses the 3 phase motor to "generate" a voltage on the unused leg by induction, thus making it useful to other motors connected down stream. But from an energy standpoint, that second (or 3rd) motor represents energy consumed to create the 3 phase power for the tool motor, so the overall energy efficiency is quite low, in the neighborhood of 60-70%. Again, for a tool running occasionally, that might not be a big deal but for something that needs to run a lot, it adds up fast in terms of cost of ownership. It also means having to start the RPC first, THEN start the tool, every time, or leave the RPC running continuously, which is a total waste of energy.

A VFD works by converting AC to DC, then back into what the motor thinks is AC. So the incoming AC can be single phase or 3 phase, it doesn't matter because it's just rectified to DC anyway. But to feed the VFD with single phase, again that current increases by 1.732, so the front end components need to be larger, plus there is more undesirable bus ripple from rectifying single phase, so you need more capacitance on the bus and the caps will run hotter. So the rule there is at least a 50% de-rate of the VFD, IF you also de-rate the operating temperature by 50%, or if you want rated operating temperature, de-rate the VFD to 35%. So for a 10HP 230V motor, you would buy at least a 20HP VFD if you can keep it at about 20C (68F), or a 30-40HP VFD is you want to use is at up to 40C (104F). If the VFD has DC Bus Chokes you can usually get away with just the 50% de-rate without the temperature de-rate, but of course that means the VFD costs more.

Another alternative is an Electronic Phase Added system that uses the equivalent o a VFD only to create the 3rd leg. They are made by a company called Phase Perfect. That might be a viable option for you here.

I would just replace the motor if it were me...
Right on.
 
A 3 phase motor will operate (meaning spin) with single phase, but will not START spinning, because there is no relative rotation direction, so it just shakes back and forth, or if it does start turning, the direction is unpredictable.

So a Static Phase Converter (SPC) at it's basic form just uses capacitors to create a phase shift in the beginning that tells the motor to start spinning in your desired direction. Once it IS spinning, then the power capacity is effectively reduced, because all of the work will be done by only 2 sets of windings. So if the motor were to be fully loaded, the current on those windings would increase by the square root of 3, or 173% and the motor would be overloaded. So if you want to use it, you must de-rate the motor by the inverse, to 58% at least, and even then the unbalanced current will cause added heating in the windings by virtue of what's called "negative sequence currents", so further de-rating is necessary. The generally accepted rule is 50% de-rate for things like tools that are not used continuously, but I always tell people if it is going to run for 3 hours or more at a time, de-rate to 33%.

A Rotary Phase Converter (RPC) takes a larger 3 phase motor that is driven by a single phase motor (Pony Motor RPC), or in some cases people use an SPC to start the 3 phase motor of the RPC so it is self contained, and uses the 3 phase motor to "generate" a voltage on the unused leg by induction, thus making it useful to other motors connected down stream. But from an energy standpoint, that second (or 3rd) motor represents energy consumed to create the 3 phase power for the tool motor, so the overall energy efficiency is quite low, in the neighborhood of 60-70%. Again, for a tool running occasionally, that might not be a big deal but for something that needs to run a lot, it adds up fast in terms of cost of ownership. It also means having to start the RPC first, THEN start the tool, every time, or leave the RPC running continuously, which is a total waste of energy.

A VFD works by converting AC to DC, then back into what the motor thinks is AC. So the incoming AC can be single phase or 3 phase, it doesn't matter because it's just rectified to DC anyway. But to feed the VFD with single phase, again that current increases by 1.732, so the front end components need to be larger, plus there is more undesirable bus ripple from rectifying single phase, so you need more capacitance on the bus and the caps will run hotter. So the rule there is at least a 50% de-rate of the VFD, IF you also de-rate the operating temperature by 50%, or if you want rated operating temperature, de-rate the VFD to 35%. So for a 10HP 230V motor, you would buy at least a 20HP VFD if you can keep it at about 20C (68F), or a 30-40HP VFD is you want to use is at up to 40C (104F). If the VFD has DC Bus Chokes you can usually get away with just the 50% de-rate without the temperature de-rate, but of course that means the VFD costs more.

Another alternative is an Electronic Phase Added system that uses the equivalent o a VFD only to create the 3rd leg. They are made by a company called Phase Perfect. That might be a viable option for you here.

I would just replace the motor if it were me...

Nice explanation. Thanks. While you are here, one more thing about phase converters that I have never understood: As I understand it, all phase converters (even the phase perfect ones) "pass through" the two single phase legs, and manufacture the third. So isnt the phase angle between all three NOT 120 degrees? How come the motor doesnt seem to care?
 

ActionDave

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Durango, CO, 10 h 20 min from the winged horses.
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Licensed Electrician
Nice explanation. Thanks. While you are here, one more thing about phase converters that I have never understood: As I understand it, all phase converters (even the phase perfect ones) "pass through" the two single phase legs, and manufacture the third. So isnt the phase angle between all three NOT 120 degrees? How come the motor doesnt seem to care?
There is also a stack of running caps in the roto phase. I'm sure that has something to do with making the VA all come out in sync.
 
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