Single phase or three phase?

682bear said:
Please explain the meaning of 'fake 3 phase' in regards to an RPC...

-Bear
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Not supplied by the Utility Company. I know I will eventually have to get a RPC but they are very expensive and noisy.

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682bear said:
Umm... L1, L2, and L3 are just 'legs'... the 'phases' are dependant on the relationship between 2 of the legs, thus L1-L2, L2-L3, and L1-L3 are the 3 phases. Am I correct on this?

Otherwise, what we call a single phase motor would actually be 2 phase, with an L1 and L2 power wire...

Or am I completely backwards?

-Bear
Click to expand...

I suppose as long as everything is safely plugged in and a person can make it go - the details of how the energy supply system is described really does not matter. I understand that certain 3 phase supplied machines are more sensitive to the source than other 3 phase machines. Certain CNC machines may not perform well on the typical RPC phase converter, but a "better" RPC is suitable for that same machine.

A single phase motor, whether 120V (L1-N) or 208V or 240V (L1-L2) is still single phase. Strictly speaking there is no such thing as 2 phase - since the sum of 2 sine waves of equal frequency is still a single sine wave - regardless of how far the shift is (the degree of shift simply impacts the amplitude in how the two waves sum).
 
Bear: It is confusing. It's sorta like you're "dropping in" a third leg in between the two existing legs kinda sorta
I'm not that great at explaining stuff otherwise I would have been a teacher
Mark
 
Bear: Most rotary phase converters run at a compromise with respect to the generated phases. There's notheing wrong with that, but the voltages may be a little off, resulting in a little more motor heating. My friend was running a 7.5HP lathe on a 10HP rotary phase converter for 39 years without a problem. You get some problems if you are running near the stall torque of your motor.

Mans Racing: If you can afford it, go for VFD/3phase every time. If you hate wiring electrical stuff and can't afford a pro job, go 1 phase for the convenience. Why? 3 PH gives you infinite speed control from 10% rated speed to more than 120% rated speed. (on some motors, 220% rated speed) It should be a little smoother (but not enough to quibble). The range is always wider on VFD rated motors.
 
Don't know the exact details David but apparently Niagara Falls at one time generated 2 phase power. Think there may still be remnants in New York state. Read about it a while ago. Given long enough we can come up with strange scenario's.

Greg
 
Well I decided to go with a 3 phase unit so I ordered a PM1440GT Lathe.Im just going to start out with a static phase converter then at a later date when I have the time I will install a VFD.Even at 2/3 power to start with it should be just fine.I was just concerned about how smooth it would run with single phase vs three phase. Thanks for all the response and help on this matter.Being very inexperienced in being a machinist I’m sure glad I found this site.
Thanks
 
682bear said:
Umm... L1, L2, and L3 are just 'legs'... the 'phases' are dependant on the relationship between 2 of the legs, thus L1-L2, L2-L3, and L1-L3 are the 3 phases. Am I correct on this?

Otherwise, what we call a single phase motor would actually be 2 phase, with an L1 and L2 power wire...
-Bear
Click to expand...
I believe that is essentially correct, however for practical wiring purposes it doesn't really matter, the "leg" can be considered a "phase".
I think the confusion over 2 "leg" power being called "single phase" Is because a single "phase" is split at the pole transformer into two "legs" (Split phase AC) and a neutral is taped from the center, either of the legs to neutral gives 120v and the to combined yield 240v.
 
Eddyde said:
I believe that is essentially correct, however for practical wiring purposes it doesn't really matter, the "leg" can be considered a "phase".
I think the confusion over 2 "leg" power being called "single phase" Is because a single "phase" is split at the pole transformer into two "legs" (Split phase AC) and a neutral is taped from the center, either of the legs to neutral gives 120v and the to combined yield 240v.
Click to expand...
Yep, that's why it seems dumb to call it 110v & 220v, I've measured mine many times while working on wiring and It's always been 249v
 
lcrepairs said:
Yep, that's why it seems dumb to call it 110v & 220v, I've measured mine many times while working on wiring and It's always been 249v
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Bonus, 249v for the price of 220!
 
The problem: RMS vs Peak to Peak voltage abbrev. PP. Gets you every time. A true RMS meter will measure 220V at most panels, but a non RMS meter will measure anywhere from 236V to 247V. BTW RMS means Root Mean Square. In a perfect world it will be .707 of the PP voltage. a good explanation (a bit over technical) is at https://en.wikipedia.org/wiki/Root_mean_square
 
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