AC phase questions

Discussion in 'General Electronics Chat' started by Capt-Killjoy, Jan 9, 2009.

  1. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    I am currently working on a DIY generator project but am a little confused with working with AC voltage. I have normal residential power to my home (240v 100amp service) and at the panel box coming from the pole I have 2 "hot wires" and one wire common to the neutral and ground busses. I was told this was single phase wiring. I don't have an oscilloscope yet to physically look at the waveform, but I would assume that the two hot wires will actually show different phase relationships from each other completing 2 of the 3 phase power that is actually available at the pole.
    If that is the case, then isn't the AC voltage available to my appliances causing harm by allowing the voltage to not stay constant because of missing the third phase signal? And why then, when I am under generator power (which I am assuming to be 3phase power) do my appliances and lights run differently? Thanks in advance for any help in understanding this. I have mainly worked with DC circuits and voltages. My experience with AC for the most part has been 'you plug it in, and it works.' :)
     
    Last edited: Jan 9, 2009
  2. mik3

    Senior Member

    Feb 4, 2008
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    The two hot wires coming into your home have a 120V rms voltage between each of them and neutral. Also, they are 180 degrees out of phase, thus the voltage between them is 240V rms. If your appliances are single phase they will be ok.
     
  3. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    Thanks for your fast response. I assume my appliances to be normal single phase. What is the harm to running 3phase power to a single phase appliance then?
    Or is there any harm?
     
  4. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    Also curious, if the signals are 180 degrees out of phase, then how does just bringing in the third 'hot wire' from the pole give you three-phase power? Not trying to sound argumentative, but I would think the phase difference would be 120 degrees. Could you explain further please?
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    You just use one of the 3 phases and the neutral of the three phase system to run a single phase appliance if the voltage of the system is the appropriate the appliance needs.
     
  6. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    So would I be correct in assuming then that the actual power going to my appliances drops to 0 volts once each cycle?
     
  7. mik3

    Senior Member

    Feb 4, 2008
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    Yes, the voltage is a sinewave and thus it passes through zero.
     
  8. mik3

    Senior Member

    Feb 4, 2008
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    I am not sure about the phase shift because in my country we have a different power system. I heard that it is 180 but I am not sure now:)
     
  9. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    If I am running on generator power (we lose power often here during storms) and my generator is putting out a 3phase 240v signal that I am backfeeding into my house panel box(after isolating the mains, of course) is this then causing harm to my appliances? I am not sure what the harm would be in running 3phase voltage into a single phase appliance if the voltage is correct.
     
  10. mik3

    Senior Member

    Feb 4, 2008
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  11. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    Thank you for the link....I will check it out right now. And thanks again for your help.
     
  12. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    That is an excellent link you provided. It answered almost every question I had. But under generator power, there is three phase power coming out isn't there? If that is the case, how will 3phase 240v power affect my appliances as opposed to single phase 240v power?
     
  13. mik3

    Senior Member

    Feb 4, 2008
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    The 240V on the 3 phase is between the phases or between the ground and each phase?
     
  14. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    I'm not sure I understand the question. The output from the generator is 240v or 110v. I am not sure what you mean about it being between the phases or the ground. I utilize the 240 output. On the generator output plug there are 4 wires coming out. The red and black wires are hot and the neutral (white) and ground (green) wires go to the same bus in the mains panel box. I am not sure if that means the 240v is between ground or phases. There is 120v available on each hot wire with relation to the ground/neutral wires. Almost exactly like the wiring on the house. But this doesn't make any sense to me as this generator is wired just like an alternator with three sets of windings. (Hence a three phase output signal, correct?) How can a generator wired this way put out a single phase voltage. Or am I just very confused?
     
  15. mik3

    Senior Member

    Feb 4, 2008
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    To make things clear, 4 wires are coming out

    one Red (phase)
    one Black (phase)
    one white (neutral)
    one green (ground)

    Is that correct?

    Then you have to get

    240V between red and black
    120V between white and black or red

    If this is the case the generator is not a 3 phase one. You don't know how the windings are wired so you can't tell if it is 3 phase or not.
     
  16. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    That is correct, as the wiring goes. I never really gave the winding configuration much thought as I assumed it would be a normal delta-wired type stator which would produce a 3phase output signal. (Knew there was a reason I shouldn't have assumed such things.) So if this is the case, could you explain how the stator would be configured to produce the single phase output it is producing? I am trying to relate all of this to a wind turbine project I have in mind, but I can't figure out how to wire my stator up to produce a single phase signal. All the plans I have studied, etc., all are designed to produce a 3phase signal, not single phase.
     
  17. mik3

    Senior Member

    Feb 4, 2008
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  18. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    Again, I thank you for the link. Looks like there is quite a bit of good info for me here. As for buying a ready made alternator, they all are designed for a 3phase output to be rectified into DC to feed a battery bank to power an inverter to get AC output as the end result. Seems to me that if you are producing AC voltage in the beginning, and you want AC voltage for your final output, there are a lot of unnecessary steps taken in between. Why not utilize the AC as it is being made as well as feed a battery bank for use when the wind isn't blowing? Just a idea I have been playing with. I have already made a couple of test alternators, and I know they are probably not the most efficient, but they are a good learning tool, I find.
     
  19. beenthere

    Retired Moderator

    Apr 20, 2004
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    The AC from the line is at a very stable 60 Hz - the AC out of an alternator spinning at a variable rate will be at an ever-changing frequency. Without a very expensive custom-designed variable input transmission, you can't get a stable frequency out of a windmill alternator.

    So it is easier to rectify and use an inverter for household use. Or a synchronous inverter if you can sell power to the utility.
     
  20. Capt-Killjoy

    Thread Starter Active Member

    Sep 29, 2008
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    I was thinking about the 60 Hz vs wind speed concern, and I agree there are a lot of things necessary to produce a clean 60 Hz AC signal from a wind generator. (Which accounts for why they are designed as they are.) But if the maximum speed that the alternator would be allowed to turn could be governed (vai gearing, etc.) wouldn't it be possible to produce a usable 60Hz signal? Keep in mind that at this point I am only concerned with keeping the signal at 60 Hz. The voltage issue will obviously be a separate (although connected) issue.
    Always appreciate your input beenthere.
     
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