Posted by amdx on April 3, 2010, 11:47 pm
> > Bob F wrote:
> >
> >> m II wrote:
> >>
> >>> If the voltage polarities were 180 apart, the neutral would carry the
> >>> SUM of the load currents. It doesn't.
> >>
> >> Really???
> >
> > This is the CORRECT web page. The author has easy to read and non
> > confusing markings. This will clear things up for everyone involved.
> 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.
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
>>wave is peaking at the top the other is at zero.
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.
> Bob F wrote:
>> m II wrote:
>>
>>> If the voltage polarities were 180 apart, the neutral would carry the
>>> SUM of the load currents. It doesn't.
>>
>> Really???
> This is the CORRECT web page. The author has easy to read and non
> confusing markings. This will clear things up for everyone involved.
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.
> 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
Posted by m II on April 2, 2010, 2:18 am
Bob F wrote:
> m II wrote:
>
>> If the voltage polarities were 180 apart, the neutral would carry the
>> SUM of the load currents. It doesn't.
>
> Really???
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
>> >
>> > So, I have three-phase power in my store and the voltage across any
>> > two hot lines is about 209. BUT, the voltage between any hot line and
>> > ground or neutral is 120 volts. SO, since I'm not going to be running
>> > any 240 volt motors etc, and the pump is running from 120 volts
>> > anyway, can I simply connect the vacuum-heat press to two legs of the
>> > three-phase plus neutral and ground? As far as I can figure I will be
>> > supplying the pump and heating elements individually with 120 anyway.
>> > Unless for some reason the heating elements require 240 but that seems
>> > like it would be an unbalanced load with the pump drawing only 120
>> > from one of the lines.
>> >
>> The reason that two legs of a 3-phase supply read 208 volts is because
>> they are 120 degrees out of phase. A single phase 240 volt (residential)
>> > supply comes from a single transformer with a a 240 volt center tapped
>> secondary. The two legs are 180 degrees apart.
>>
>> So on a 3 phase supply, one leg will rise up to 120volts, but the other
>> leg will not be at -120 volts. It will be at about -88volts (if i did
>> the head math correctly).
>>
> Your math is ahh, hmm, depends how you think about it :-)
> You almost need to think in peak and peak to peak terms when you
> are discussing 3 phase and measuring phase to phase.
> When one phase peaks it is 169.68 volts above ground, (1.414 x 120V)
> The other leg must be -124.43V, because 124.43 + 169.68 = 294.11 Vpp.
> And 294.11V x .707 = 208 V
> And yes you're correct 88V x 1.414 = 124.43Vp
> What I'm a bit puzzled by is I can't find a proper graph.
> The negative leg is never at the correct point to show what I have said.
> Mike
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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> >
> >> m II wrote:
> >>
> >>> If the voltage polarities were 180 apart, the neutral would carry the
> >>> SUM of the load currents. It doesn't.
> >>
> >> Really???
> >
> > This is the CORRECT web page. The author has easy to read and non
> > confusing markings. This will clear things up for everyone involved.
> 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.