2 phase electric motor

Discussion in 'General Electronics Chat' started by electronis whiz, Nov 26, 2011.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    we just got an air compresor from an old body shop. it sounds like it is 2 phase. is this 120 hot- 120 hot for 220 wirth no nutral? if not how is it setup. somthing i read said most american houses only have single phase service however i think thats wrong. at least in our area there are 3 wires to most every house. 2 insilated hots and a bare nutral. is'nt this 3 phase? so 2 phase should just be 120-120 with no nutral.
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    In North America the electricity is delivered to your home as 240V with a grounded center-tap (neutral) . The electric clothes dryer and electric stove use 240V. Some electric outlets use one of the 120V wires and neutral and other outlets use the other 120V wire and neutral. In the kitchen a dual receptacle will have 120V plus 120V, each with a neutral.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    3-phase has three hot wires with the phase of each wire 120 degrees from the other two.

    2-phase has 4 hot wires with the phase 90 degrees between them.

    As AG stated the 3 wires into the home is single-phase 240V with a center tap to give 120V to the center-tap. Each hot wire appears to be 180 degrees out of phase with the other when measured to the center-tap common.
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I seriously doubt it's "2-phase". As far as consumer products go, there are only single phase and 3phase motors. 2-phase motors exist but their use is quite limited. they were the predecessor of 3 phase motor, and were used in a few dams and such, but really aren't used anywhere else. a 2-phase motor has 4 wires; 2 seperated isolated single phase windings.

    if its 240V, its probably 240V single phase.
     
  5. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    thanks for the help. the person we got it from said it was 2 phase i kind of thought that was odd. turns out i read the label and it was only a single phase. got it wired up yesterday and worked fine.
    why is 2 phase called that if there are 4 hot wires? seems it would be 4 phase
     
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  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    single phase has 2 wires. 2phase is simply 2 isolated (from eachother) single phases, so 4 wires. Imagine you take a single phase motor and add another single phase motor coupled to it; now you feed to seperate isolated single phase supplies, 90 electrical degrees out of phase. this negates the need for start/run caps; it was the precursor to 3phase, before 3phase was fully understood.
     
  7. jimkeith

    Active Member

    Oct 26, 2011
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    A little trivia...
    I think the last place 2 phase was used in the US was Niagara Falls. Its 2 phase generator was installed in 1895--at the time it was the largest in the world.

    http://en.wikipedia.org/wiki/Two-phase_electric_power
    http://www.3phasepower.org/2phasesystems.htm

    When 3 phase came of age (about the same time), a bright engineer named Charles F. Scott came up with the Scott transformation or Scott T transformer that converted 2 phase to 3 phase. In this way, the old 2 phase generators could be connected to the 3 phase grid.

    Today about the only two phase motors used are stepper motors.

    Back in the 70's, I worked with Precise Rockwell who manufactured 64,000 RPM direct drive spindles that used 2 phase motors--initially, they were driven by Motor-Generator sets--later by 3 phase inverters utilizing a Scott T transformer. Very noisy!
     
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  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    This is commonly known as "split phase" or "split phase 220", left half of breaker panel is the "top part" of the transformer, right half of breaker panel is the "bottom half" of the transformer, with neutral being the center tap. The idea is to load the left and right sides of the breaker panel as evenly as possible.

    Since they are out of phase by 180, either hot wire to neutral is single phase 110V, but there is single phase 220V between the two hot wires as well. Some appliances, such as electric dryers, use a 220V hookup, but are 110V inside, as one 110V side drives the tumbler motor, and the other 110V side drive the heating elements.
     
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  9. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    As I am working toward a two phase motor project I've done some research on it. Heres a good link if anyone is interested; http://www.3phasepower.org/2phasesystems.htm

    The new motors in the Chevy Volt car are two phase, although their listed as three phase on some web sites. Most of the literature on the Volt just says "poly-phase motor"

    Tesla's original poly-phase induction motors were two phase. That was what he worked with and maybe the secret to unlocking his experiments that everyone says don't work. From what I've read people are trying to duplicate his work by using either single or three phase. Or I'm wrong :)
     
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  10. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I read also that someone is doing a 2phase EV motor project. it seems like a plenty good idea to me for an EV. I think the only reason why 3 phase won out for power distribution is because the expense of the 4th wire. in an EV thats not a big issue.
     
  11. jimkeith

    Active Member

    Oct 26, 2011
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    @ shortbus: Love the link--and the photo of the big, ugly transformer.

    Hilarious, the reference to the 2 phase 'clock' used in AMD CPUs...
     
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I thought we've duplicated and improved on all of Tesla's useful work, from induction motors to radio?

    Don't tell me you are going....there.?:eek:
     
  13. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    @thatoneguy- no not going there. but maybe if someone did with two phase they could replicate it. Still think that it will happen some day. Not in my life time though.
     
  14. BillB3857

    Senior Member

    Feb 28, 2009
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    The radar antenna(s) used on the plane in my avitar used 2 phase motors driven by magnetic amplifiers. One phase excited by a reference voltage (400hz) and the other by a variable voltage from the magamp. The magamp had the ability to flip the phase of its output 180 degrees for reversal of the motor. The variable amplitude out of the magamp controlled the torque (speed) of the motor. Haven't heard of many magamps in use today.
     
  15. Audioguru

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    Dec 20, 2007
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    A Super Connie? I was in one about 56 years ago.
     
  16. shortbus

    AAC Fanatic!

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    @BillB3857 - one place that mag-amps are used is in amperage control of tig and mig welders. A DC coil around a AC coil to control the out-put amperage.
     
  17. BillB3857

    Senior Member

    Feb 28, 2009
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    Thanks for the info, Shortbus. Never too old to learn something!
     
  18. jimkeith

    Active Member

    Oct 26, 2011
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    @shortbus & BillB3857: As late as about 1980 or so, Fincor manufactured DC drive control mag amps in the order of 60 to 100HP. Of course, these were manufactured as replacements or add-ons to existing systems as all cataloged DC drives were at that time thyristor controlled. Now this was true 'solid state reliability' --these boat anchors were rugged and ugly and noisy as they sang out many strange audible harmonics... They maintained their own magnetics shop for many years after this stuff became prohibitively expensive and obsolete to retain this manufacturing capability.

    They utilized large cut-core magnetics that were characterized by 'square loop' saturation of the B/H curve. They also utilized selenium rectifiers--I can still smell the odor they emitted when the smoke escaped...

    Some of the smaller stuff was developed during WWII and used for shipboard gun turret controls etc.

    I was never involved in this stuff and considered this technology a black art as my understanding was abysmal. This generation of bright engineers are all gone now, but I had the privilege of rubbing shoulders with a few of them.
     
  19. shortbus

    AAC Fanatic!

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    People also say there are no two phase motors in use today. But a capacitor start - capacitor run motor is in effect a two phase. The run capacitor puts a set of windings 90* out of phase, thus a "two phase" motor, running on single phase.
     
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