dumb question about quick charging

lorenfb · Jul 1, 2019

LeftieBiker said:
Probably the easiest way to explain it is that if you "split" something, there is only one of it.

What? And how would you "split" a sine wave voltage source? Maybe use another tap on the line transformer which is 180 degrees
out of phase? And call that the out-of-phase 120V RMS line relative to the neutral line input.

LeftieBiker said:
You then end up with two halves that together still add up to just one.

Right, two voltage phases when measuring between the two phases that add up to just one phase. You do understand,
and no need for wiki!

smkettner · Jul 2, 2019

lorenfb said:
smkettner said:

Homes in the US are generally 240v, split phase. This is single phase service. Commercial or industrial may have three phase.

No two phase. Fun to argue though because 'phase' has two different meanings that apply. Wiki explains it better than I can.

Click to expand...

There are two phases or a split phase for those that like to parse words and need to refer to wiki
i.e. each line is 180 degrees out of phase (an angle):

Vphase1 = Vrms x sin (A)
Vphase2 = Vrms x sin (A+180)

Vphase3 = Vphase1 - Vphase2 (any phase other than 180 degrees results in less than 240V RMS)
A three phase system has three phases, each 120 degrees out-of-phase with each phase.

And for those that must always refer to wiki; https://en.wikipedia.org/wiki/Phase_(waves)

In physics and mathematics, the phase of a periodic function F of some real variable t is the relative value of that variable within the span of each full period.

Click to expand...

Should we continue parsing terms?

OK skip Wiki. There are plenty of electricians pages and blogs that explain single vs three phase.
None that explain two phase. Maybe because ?????

https://www.elprocus.com/difference-between-single-phase-and-three-phase-ac-power-supply/

LeftieBiker · Jul 2, 2019

https://www.elprocus.com/difference-between-single-phase-and-three-phase-ac-power-supply/

I was squirming at the grammar and syntax in the above, when it occurred to me that this is probably a European article, written by someone for whom English is a second language. European grid power is at least almost universally single phase 230 (?) volts. There is no 120 volt grid to speak of, so they don't talk about split phase 240 volt systems. The piece thus describes single phase as having 230 volts. At least that's my take on it...

Nubo · Jul 2, 2019

lorenfb said:
Should we continue parsing terms?

No need for parsing. It's a matter of convention. Electrical engineers have decided what "multiphase" and "single phase" mean for electrical distribution. I'm guessing they're more concerned with the "phase" running to the local transformer, and the split there is more of a niggle.

And in fact, per the wiki:

Since the two phasors do not define a unique direction of rotation for a revolving magnetic field, a split single-phase is not a two-phase system.

Seems like the output waveform(s) from the generator are what the semantics are based upon.

SalisburySam · Jul 2, 2019

RustyShackleford said:
lorenfb said:

That's the best you can contribute, parsing words?

Click to expand...

You're wrong, period. In science/engineering, specific words are very important, such as the difference between 90 degrees and 180 degrees. I don't want to "pull rank", but I am imminently qualified on electrical matters.

Agree words are important. Which is why being imminently (happening very soon) qualified is very, very different from eminently (to a notable degree) qualified.

RustyShackleford · Jul 2, 2019

SalisburySam said:
RustyShackleford said:

lorenfb said:

That's the best you can contribute, parsing words?

Click to expand...

You're wrong, period. In science/engineering, specific words are very important, such as the difference between 90 degrees and 180 degrees. I don't want to "pull rank", but I am imminently qualified on electrical matters.

Click to expand...

Agree words are important. Which is why being imminently (happening very soon) qualified is very, very different from eminently (to a notable degree) qualified.

Touche'.

GlennD · Jul 2, 2019

Agreed, ,. Most houses have a center tapped single;e phase circuit. From both legs ignoring the neutral is 240vVAC

lorenfb · Jul 3, 2019

GlennD said:
Agreed, ,. Most houses have a center tapped single;e phase circuit. From both legs ignoring the neutral is 240vVAC

So there're really two phases 180 degrees out of phase, referenced to the neutral (the transformer's center tap), at the house's
main panel. Most couldn't care less what happens at the power compamy's line transformer. When I put my dual trace scope probes,
on each line referenced to neutral, the display indicates two sine waves 180 degrees out of phase.

Hardly that complex! Some still failing to understand the issue?

SalisburySam · Jul 3, 2019

lorenfb said:
GlennD said:

Agreed, ,. Most houses have a center tapped single;e phase circuit. From both legs ignoring the neutral is 240vVAC

Click to expand...

So there're really two phases 180 degrees out of phase, referenced to the neutral (the transformer's center tap), at the house's
main panel. Most couldn't care less what happens at the power compamy's line transformer. When I put my dual trace scope probes,
on each line referenced to neutral, the display indicates two sine waves 180 degrees out of phase.

Hardly that complex! Some still failing to understand the issue?

No difficulty understanding the aspects of phasing. There is also no difficulty understanding that there is really no two-phase terminology convention used in the US for home power. The convention, regardless of if technically a two-phase scenario exists, is the home power is single or split-phase.

I agree that few care about what goes on at the transformer, even less care about the technical distinction of power phases.

lorenfb · Jul 3, 2019

SalisburySam said:
lorenfb said:

GlennD said:

Agreed, ,. Most houses have a center tapped single;e phase circuit. From both legs ignoring the neutral is 240vVAC

Click to expand...

So there're really two phases 180 degrees out of phase, referenced to the neutral (the transformer's center tap), at the house's
main panel. Most couldn't care less what happens at the power compamy's line transformer. When I put my dual trace scope probes,
on each line referenced to neutral, the display indicates two sine waves 180 degrees out of phase.

Hardly that complex! Some still failing to understand the issue?

Click to expand...

No difficulty understanding the aspects of phasing. There is also no difficulty understanding that there is really no two-phase terminology convention used in the US for home power. The convention, regardless of if technically a two-phase scenario exists, is the home power is single or split-phase.

Good, so you're beginning to understand! When wiring a house, most (not brain dead) think in terms of two phases and how to
distribute/load the two phases at the main panel. Thinking in terms of a single phase at the main panel provides no insight whether
installing new breakers or solving a partial power failure in the house. Ever attempted to determine which of the two phases powers
what areas of your house? Maybe do a wiki search, right?

Still having a problem?

SalisburySam said:
I agree that few care about what goes on at the transformer, even less care about the technical distinction of power phases.

Wrong!

SageBrush · Jul 3, 2019

lorenfb said:
Ever attempted to determine which of the two phases powers
what areas of your house?

No, but as one of the brain dead I'd like to know the answer without the aid of a scope.
Any chance one phase goes to the left side of the panel and the other phase to the right ?
Addendum: Nope.
http://www.oempanels.com/208v-single-phase-and-208v-3-phase
Sheesh

And while I am on a roll of ignorance ... I'd like to understand 208 volt from a 120 volt WYE config (two phases connected)
I calculate it as 120 + 120*cos(pi/3) = 180 volts. Why is that wrong ?

Peace

lorenfb · Jul 3, 2019

SageBrush said:
lorenfb said:

Ever attempted to determine which of the two phases powers
what areas of your house?

Click to expand...

No, but as one of the brain dead I'd like to know the answer without the aid of a scope.
Any chance one phase goes to the left side of the panel and the other phase to the right ?
Addendum: Nope.
http://www.oempanels.com/208v-single-phase-and-208v-3-phase
Sheesh

And while I am on a roll of ignorance ... I'd like to understand 208 volt from a 120 volt WYE config (two phases connected)
I calculate it as 120 + 120*cos(pi/3) = 180 volts. Why is that wrong ?

Peace

Calculate Vrms = Vin (peak) x sqrt (1/2) x (1/pi) times the integral of: (sin(X) + sin(X+120) dx) |0 to 2pi

where Vin(peak) = Vrms X sqrt (2 )= 120 X 1.414 = 170 volts

If the phase angle were 180 degrees then the result is 240 versus 208.

Sorry for not being able to have the scientific keyboard characters. You'll get the idea.
Just a little integral calculus is all you need to remember.

lorenfb · Jul 3, 2019

For those that think that they understand residential power systems, consider what happens when the neutral power
line loses connection at the power pole, and your residence truly has a single phase (240 RMS, 340 PEAK) connected
to all your internal electrical devices, e.g. that switching power supply in your desktop PC, TVs & other electronics.

SageBrush · Jul 3, 2019

lorenfb said:
Calculate Vrms = Vin (peak) x sqrt (1/2) x (1/pi) times the integral of: (sin(X) + sin(X+120) dx) |0 to 2pi

Oh ... I see. Thanks!

lorenfb · Jul 3, 2019

SageBrush said:
lorenfb said:

Calculate Vrms = Vin (peak) x sqrt (1/2) x (1/pi) times the integral of: (sin(X) + sin(X+120) dx) |0 to 2pi

Click to expand...

Oh ... I see. Thanks!

Correction:

Vrms^2 = Vin (peak)^2 x (1/2pi) times the integral of: (sin(X) - sin(X+120))^2 dx |0 to 2pi
A book of math tables can be used to solve the above.

The simple case of being 180 degrees out of phase is; Vrms = 2 x Vin (peak) / sqrt (2) = 2 x Vin (RMS)

SageBrush · Jul 3, 2019

lorenfb said:
SageBrush said:

lorenfb said:

Calculate Vrms = Vin (peak) x sqrt (1/2) x (1/pi) times the integral of: (sin(X) + sin(X+120) dx) |0 to 2pi

Click to expand...

Oh ... I see. Thanks!

Click to expand...

Correction:

Vrms^2 = Vin (peak)^2 x (1/2pi) times the integral of: (sin(X) + sin(X+120))^2 dx |0 to 2pi
A book of math tables can be used to solve the above.

The simple case of being 180 degrees out of phase is; Vrms = 2 x Vin (peak) / sqrt (2) = 2 x Vin (RMS)

When I looked at a picture of two vectors at 120 degrees to each other representing the voltage of each line I decided that the vector sum would remain constant. It still looks that way to me but it cannot be right and be AC :| so your integral is the way to go.

As for the details of calculating RMS of a waveform ... it is a distant memory.
When a multimeter measures 120 volts on an AC leg, is that an RMS value ?

GerryAZ · Jul 4, 2019

Sagebrush,

Multimeters are generally calibrated to display RMS voltage for sine waves. Depending upon their measurement methods, they may display incorrect voltages for other waveforms. True RMS meters will display RMS voltages for any waveform. For a sine wave, the RMS value is the peak value divided by the square root of 2. You are looking at the vectors correctly--line-to-line voltage between two phases (on a wye-connected transformer secondary) is the vectorial sum of the line-neutral voltages of those phases. The line-to-line voltage is the square root of 3 times the line-neutral voltage (120 Times Square root of 3 equals 208).

lorenfb · Jul 4, 2019

SageBrush said:
lorenfb said:

SageBrush said:

Oh ... I see. Thanks!

Click to expand...

Correction:

Vrms^2 = Vin (peak)^2 x (1/2pi) times the integral of: (sin(X) + sin(X+120))^2 dx |0 to 2pi
A book of math tables can be used to solve the above.

The simple case of being 180 degrees out of phase is; Vrms = 2 x Vin (peak) / sqrt (2) = 2 x Vin (RMS)

Click to expand...

When I looked at a picture of two vectors at 120 degrees to each other representing the voltage of each line I decided that the vector sum would remain constant. It still looks that way to me but it cannot be right and be AC :| so your integral is the way to go.

As for the details of calculating RMS of a waveform ... it is a distant memory.
When a multimeter measures 120 volts on an AC leg, is that an RMS value ?

The RMS voltage calculation determines what power will be developed from a particular voltage waveform.
RMS - root mean squared - the sqrt of the time average of the integral of the squared voltage function

SageBrush · Jul 4, 2019

GerryAZ said:
Sagebrush,

Multimeters are generally calibrated to display RMS voltage for sine waves. Depending upon their measurement methods, they may display incorrect voltages for other waveforms. True RMS meters will display RMS voltages for any waveform. For a sine wave, the RMS value is the peak value divided by the square root of 2. You are looking at the vectors correctly--line-to-line voltage between two phases (on a wye-connected transformer secondary) is the vectorial sum of the line-neutral voltages of those phases. The line-to-line voltage is the square root of 3 times the line-neutral voltage (120 Times Square root of 3 equals 208).

Thanks for chiming in !

Would you mind showing the vector math that results in 120*sqrt (3) ?

I came up with 120 + 120*Cos(pi/3) = 120*1.5 but that is incorrect. I suppose it means that I cannot simply take the vectorial sum of the two RMS voltages

SageBrush · Jul 4, 2019

This (mostly) brain-dead person just had one cell light up.
208 volts it is on a WYE when measured between two 120 volt legs. All I needed was to add vectors correctly

Thanks to Gerry for the kind redirection.

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