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240VAC single phase from three-phase? - Page 10

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Posted by amdx on April 3, 2010, 11:47 pm
 




  Hi Ulysses,
 Out of phase could be only 1 degree out of phase. What you described,

 >>I  thought OUT of phase meant that when one

 The could be 90 degrees or 270 degrees out of phase, depends whether the
zero line is headed pos or neg.
 180 degrees out of phase would be if L1 is a the positive peak
and L2 is at the negative peak.
 I added some more info to support my assertion at 8:59 PM and
9:37 pm , 04-02-10.
 See if it helps or if you disagree.
                    Mike (amdx)



Posted by Josepi on April 4, 2010, 3:31 am
 


Mike has it confused in his analogy.

If you want to compare 120/240 with batteries you have to use the same
reference point

In 120/240 vac we use the common (neutral) as a reference point the two
phases are 180 deg out of phase with each other. We have 120vac and 120vac
out of phase with each other, from that reference point. We have a total of
240vac as positive one leg (+120vac) subtract the other leg (-120vac) = 240
vac (think phasors).

If we use (an say make it grounded) a 240 volt leg instead then both phases
would be in phase with each other and add to 240 vac.


To use the battery analogy we have to use the common connection between
batteries as analogous to neutral in a 120/240vac system. Now you have one
+12v and one -12v end.


So it depends where you are standing (point of view). If you stand behind
two people,  they are both in front of you,  but if you stand between them
one is in front and one is behind you.



I probably shouldn't say this but it muddies it up for me.  Without seeing
the sine waves and seeing the phases I can't tell if they are in-phase or
out-of-phase.  And aside from all of that I thought you got 240 from the two
120 volt coils if they were OUT of phase with each other, not IN phase.
Perhaps I'm just not understanding what IN and OUT of phase means.  I
thought OUT of phase meant that when one sine wave is peaking at the top the
other is at zero.  Is this wrong?  I have rewired generator heads many times
in order to either get 240 volts OR 120 volts in parallel (to balance the
load on the coils) and, in my mind (which can be a frightening place) the
sine waves were going up and down at the same time so 120 was all I was
going to be able to get.  Kinda like connecting two batteries in parallel.





I probably shouldn't say this but it muddies it up for me.  Without seeing
the sine waves and seeing the phases I can't tell if they are in-phase or
out-of-phase.  And aside from all of that I thought you got 240 from the two
120 volt coils if they were OUT of phase with each other, not IN phase.
Perhaps I'm just not understanding what IN and OUT of phase means.  I
thought OUT of phase meant that when one sine wave is peaking at the top the
other is at zero.  Is this wrong?  I have rewired generator heads many times
in order to either get 240 volts OR 120 volts in parallel (to balance the
load on the coils) and, in my mind (which can be a frightening place) the
sine waves were going up and down at the same time so 120 was all I was
going to be able to get.  Kinda like connecting two batteries in parallel.




Posted by m II on April 2, 2010, 2:18 am
 

Bob F wrote:


This is the CORRECT web page. The author has easy to read and non
confusing markings. This will clear things up for everyone involved.


http://www.allaboutcircuits.com/vol_2/chpt_10/1.html


The last posting with the wrong URL went out by mistake and I can't
cancel it.




mike


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Posted by amdx on April 5, 2010, 5:33 pm
 



 Hey guys I got this wrong, The peak of the 120 volt line is 169.68 volts,
however,
when you use two lines to get 208Vrms the 294Vpeak is 30 degrees from the
120Vrms peak. (peaks at 169.68)
At that point in the waveform one 120V line has reached +146.97 and the
other
is at -146.97 for a difference of 293.94Vpeak. This equals 208Vrms.
 Here is a very nice graph to show the relationship between the 120V 3 ph
and the
208 V line.
http://i145.photobucket.com/albums/r...3waveforms.gif
       Mike (amdx)



Posted by Josepi on April 5, 2010, 6:51 pm
 

Yup, voltages at 120 degress apart.

Vectorial total  gives us
120 x cos(30) - 120 x (cos(150) = 207.846vac




 Hey guys I got this wrong, The peak of the 120 volt line is 169.68 volts,
however,
when you use two lines to get 208Vrms the 294Vpeak is 30 degrees from the
120Vrms peak. (peaks at 169.68)
At that point in the waveform one 120V line has reached +146.97 and the
other
is at -146.97 for a difference of 293.94Vpeak. This equals 208Vrms.
 Here is a very nice graph to show the relationship between the 120V 3 ph
and the
208 V line.
http://i145.photobucket.com/albums/r...3waveforms.gif
       Mike (amdx)




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