single phase to 3 phase converter

Status
Not open for further replies.
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
If a 3 phase motor is rated 40 amps and the building only has single phase then you can use a phase converter. I have never wired a phase converter but I was wondering since there is only single phase feeding the converter would you need to upsize the wire or would you still pull a 40 amp 220 single phase circuit to the converter? If you do upsize how does one figure this?
 
Dennis Alwon said:
If a 3 phase motor is rated 40 amps and the building only has single phase then you can use a phase converter. I have never wired a phase converter but I was wondering since there is only single phase feeding the converter would you need to upsize the wire or would you still pull a 40 amp 220 single phase circuit to the converter? If you do upsize how does one figure this?
Click to expand...

Watts is watts :smile:, disregarding converter losses the motor will require the same KW from the single phase line as the three phase line.
 
iwire said:
Watts is watts :smile:, disregarding converter losses the motor will require the same KW from the single phase line as the three phase line.
Click to expand...

Thanks Bob-- I guess I was wondering if the converter loss was significant to consider. Sounds like it is a no issue.
 
Dennis Alwon said:
If a 3 phase motor is rated 40 amps and the building only has single phase then you can use a phase converter. I have never wired a phase converter but I was wondering since there is only single phase feeding the converter would you need to upsize the wire or would you still pull a 40 amp 220 single phase circuit to the converter? If you do upsize how does one figure this?
Click to expand...
Dennis, 40A at 208/3/60 will be probably 15HP. To get that from single phase will be a big converter. I'd pursue a 3 ph service. _I_ would use an inverter for the conversion. I'm not sure the single phase in go that large.
 
GeorgeB said:
Dennis, 40A at 208/3/60 will be probably 15HP. To get that from single phase will be a big converter. I'd pursue a 3 ph service. _I_ would use an inverter for the conversion. I'm not sure the single phase in go that large.
Click to expand...

That was purely hypothetical. A cabinet shop called me and asked about it. I suspect the unit is 5 hp or so but I don't know.

I suggested changing the service bt he said he could get an inverter for this unit for $500--- He was renting and doesn't want to go the service change route.
 
Dennis Alwon said:
Thanks Bob-- I guess I was wondering if the converter loss was significant to consider. Sounds like it is a no issue.
Click to expand...

Dennis I really don't know but I imagine that info would be provided for each converter.

There are motor/generator converters, rotary converters and some VFDs can be used to do it.
 
080521-1627 EST

Dennis:

If your 3 phase motor is really 40 A per leg at 220 leg to leg, then my rough calculation is 3 * 40 * 127 = 3 * 5100 VA = 15,300 VA. There is some inefficiency in the rotary converter so you would need to figure more, but lets just use 15,300, then the 220 single phase has to supply 15,300 / 220 = 70 A.

Edit: A rotary phase converter, an induction motor with capacitors, only supplies the 3rd leg deriving power from the first two legs.

.
 
Last edited:
gar said:
080521-1627 EST

Dennis:

If your 3 phase motor is really 40 A per leg at 220 leg to leg, then my rough calculation is 3 * 40 * 127 = 3 * 5100 VA = 15,300 VA. There is some inefficiency in the rotary converter so you would need to figure more, but lets just use 15,300, then the 220 single phase has to supply 15,300 / 220 = 70 A.

Edit: A rotary phase converter, an induction motor with capacitors, only supplies the 3rd leg deriving power from the first two legs.

.
Click to expand...

So you are saying that I would need to supply 70 amps for that 40 amp 3 phase load? I assume the converter will give this info????
 
Dennis sticking with the 40 amp load.

40 amps at 208 3 phase is 14,300 watts

14,300 watts with 240 single phase will be 59 amps or so.

So the supply would have to provide a minimum of 59 amps single phase to the converter in order for it to output 40 amps 3 phase 208. plus any losses in the converter.
 
Last edited:
Bob pretty much hit on the spot with the figures and for 40 amp 3? load to order run from 1? phase supply it will use at least 70 amp 1? load to the converter.

But becarefull if that equiment do have 1? load for some reason like L-N load do not hook up to C phase due oddball voltage will show up on C phase L-N leg.

Merci,Marc
 
iwire said:
So the supply would have to provide a minimum of 59 amps single phase to the converter in order for it to output 40 amps 3 phase 208. plus any losses in the converter.
Click to expand...
Bob, won't the output also be 240v, since two of the three lines are simply the supply lines fed through?
 
080521-1952 EST

Dennis:

I believe a lot of rotary converters, meaning a normal induction motor with some phase shift capacitors, are homemade or by small companies that may not provide much information about the drive. It seems that some users have to play with capacitor values.

Note: a normal induction motor is not a very good generator (alternator) and there is a moderate loss in the converter. A lot of the energy is thru the capacitors. Often times to get good voltage balance one has to adjust the capacitors, and this is load dependent.

Whatever the single phase input voltage is will be the desired leg-to-leg voltage for each of the three phases. To repeat the single phase legs are simply a pass thru to the load.

If the motor is not too large, 5 HP is probably the limit, then I would favor a single phase input vector drive control. You get variable speed, torque limiting, acceleration and deceleration control. And in the future it is useful for some other application.

The long procedure that I presented above in my previous post was to illustrate a technique of converting from delta to Y for you to have an intutuive way to solve certain problems. If a delta or Y load dissipates the same power then the leg current is the same for both loads. In the case of the Y and a resistive load I know that the leg current and leg to neutral voltage are in phase. All of this assumes a balanced circuit. You know or can use a simple vector diagram to calculate the leg to neutral from the leg-to-leg voltage. Also probably it is easy to remember this ratio is very close to 120/208. So now in the Y load the power per leg for a resistive load is Ileg * Vleg-to-neutral. Total power is of course 3 times times this one leg power. Note: 120/208 = 1/sq-root of 3 = 1/1.732 = 0.577350269 .

To have a self starting motor all that is required is some crude form of a rotating magnetic field. In a good three phase motor or alternator design this is nearly a constant amplitude rotating vector.

Single phase motors, at least to get started, are some form of a two phase motor, and therefore some approximation to a constant amplitude rotating magnetic field, but not very good.

You might be able to use capacitors to get a three phase motor started and then run it single phase as a reduced output motor.

If you are in the 5 HP range look at vector drives. I haven't found a single phase 5 HP drive with a quick search, but I believe I saw one a while back. Here is one reference for 3 HP.
http://www.driveswarehouse.com/advs...Horsepower=3.00&IVoltage=6&OCurrent=&x=29&y=7

I believe there are some phase converters that use only capacitors and maybe some inductors.

.
 
That you all for the incredible info you have given me. As many of you know I am a resi guy so this stuff is totally new to me. Not sure I will even take the job but I was very interested in understanding it. Thanks again.
 
phase convertors

phase convertors

It has been many moons ago since I installed a phase convertor. The requirement was for an embroidery business. Rented commercial space. building had single phase service. Machines required 3 phase power. These were basically $90,000 sewing machines(15 heads). What made it easy was that the manufacture of "stich" machines had provided the phase convertors(ended up doing 2).Pulled circuit to starters and mounted convertors on pads.Art. 455 covers what you need as far as install. As gar noted in his post, a lot of these convertors are pretty simple, that appear "homemade"!
 
LarryFine said:
Bob, won't the output also be 240v, since two of the three lines are simply the supply lines fed through?
Click to expand...

I would say that would depend on the type of converter used. :smile:

A motor / generator could have entirely different input and output voltages.
 
LarryFine said:
Bob, won't the output also be 240v, since two of the three lines are simply the supply lines fed through?
Click to expand...

Larry.,,

Hate to step in but yes ., most low to med grade converters are used the two incomming line from supply while the thrid phase is " manufactered " by either capaitors or combation of useing a " idler " motor with capaitors.

That reason why most peoples were not really aware with third phase have oddball action sorta like wild leg if you get my point. and that the whole moot point when someone hook up equiment and not aware with single phase load reqirement that part useally catch someone off guard if not paying attetion on this one.

Merci,Marc
 
frenchelectrican said:
Larry.,,

Hate to step in but yes ., most low to med grade converters are used the two incomming line from supply while the thrid phase is " manufactered " by either capaitors or combation of useing a " idler " motor with capaitors.
Click to expand...

I agree when we talking about standard rotary converters. :smile:

Here is a Rotary phase converter, basically it's just a three phase motor you supply single phase and you use the 'extra' conductor along with the two from the supply as the three phase supply. As Marc pointed out this manfactured phase can not be used for line to neutral loads.

Rotary_Converter_3_Phase_Power.jpg



Here is a motor - generator converter, the input voltage, frequency, phase has absolutely no influence what output voltage, frequency or phase could be.

TEMCoMGSet.jpg


I have helped install a unit like this for frequency conversion (60 to 50)
 
Status
Not open for further replies.
Top