Center-tap Transformer Voltages

[pfalcon]

That is not the answer. I want to know the magnitude and phase of Vx1x2 and Vx4x3 in a split phase system.

Staying with the picture RonaldRC provided, since I often can't see yours.

Presuming the standard convention of + to - being <0; Presuming V12 therefore to be +120<0; We now have two cases:

1) As pictured with a primary coil V34 = +120<0 and therefore V14 = V12 + V34; Placing you leads backward to get V43 fails to match polarity with your circuit. Therefore you fail your quiz.
2) Ignoring the presence of the primary coil; What would you like? V34 = +120<0 or V43 = -120<180? So V14 = V12 + V34 = V12 - V43. Your choice. Have fun. Don't be an engineer.

 

[rattus]

Staying with the picture RonaldRC provided, since I often can't see yours.

Presuming the standard convention of + to - being <0; Presuming V12 therefore to be +120<0; We now have two cases:

1) As pictured with a primary coil V34 = +120<0 and therefore V14 = V12 + V34; Placing you leads backward to get V43 fails to match polarity with your circuit. Therefore you fail your quiz.
2) Ignoring the presence of the primary coil; What would you like? V34 = +120<0 or V43 = -120<180? So V14 = V12 + V34 = V12 - V43. Your choice. Have fun. Don't be an engineer.

I want to know the phase angles seen on L1 and L2 of a split phase system! Voltages measured relative to the neutral.

 

[gar]

111121-1953 EST

What happens when you add two sine waves of equal magnitude together where one sine wave is 180 degrees out of phase with respect to the other?

Get a two input analog adder circuit with equal gain on both inputs. Connect the adder's common to the transformer center tap. Connect one adder input to one end of the secondary, and the other adder input to the other end of the secondary. What is the output of the adder?

.

 

[mivey]

Anything else gets a big fat F on your test...In engineering we're taught not to abuse circuit equivalencies. So both <0 or both <180 will get you a pass on the test while one of each will get you an F.

Then we must be talking about two different things because I usually aced mine.

...Unless you're designing transformers this thread is irrelevant. +<0, -<180, it all works out the same if you're working exclusively on one side or the other of the transformer, or even with a virtual transformer.

ONLY if you're going to include the physical transformer does the polarity of the secondary voltages matter. Then based on the actual physical turns in the transformer the secondaries will both be <0 or both be <180. Nobody reverses the turns midway through the windings.

You are trying to tie absolutes into some neat little knot but it is just not that way. Little snap-shots in time do not paint the complete picture.

Consider the battery that keeps being used as an example:
Do you realize that there is bi-directional flow inside the battery, and that the electrons are not flowing in the battery? On the other hand, we have electrons as charge-carriers in the wire. But that does not paint the complete the picture of what is going on in the circuit. Also, the charge carriers are flowing against our current direction.

But what does all that have to do with our use of taking our current direction to be from the positive terminal to the negative terminal of the battery through the load? We could focus on the one physical aspect, then ignore the other, then claim someone is going against some physical reality. That is what you are doing.

 

[rattus]

111121-1953 EST

What happens when you add two sine waves of equal magnitude together where one sine wave is 180 degrees out of phase with respect to the other?

Get a two input analog adder circuit with equal gain on both inputs. Connect the adder's common to the transformer center tap. Connect one adder input to one end of the secondary, and the other adder input to the other end of the secondary. What is the output of the adder?

.

Gar, Are you using Philbrick op-amps?

 

[mivey]

Isn't a difference in phases a difference in time also?

That is a fair question and the problem is there are too many varied uses of the word phase.

The technically-correct definition is that the phase is any point on an AC wave. With that, the phase difference on a single wave is a time difference, either expressed in time or degrees. But we also may compare the phase of one wave with the phase of another wave and these can represent (among other things):
1) The same physical condition at a difference in time.
2) A physical difference at the same instant in time.

Given the technical definition of phase, single-phase implies one AC voltage or current in a circuit. By definition, a two-wire circuit has one voltage and one current and must be single-phase. Polyphase voltages or currents have more than one phase at any instant, so a polyphase circuit must have more than two wires. Now comes the argument: when we have more than two wires.

One issue is that there are multiple uses of the word "phase". In addition to the technically-correct one I gave above, we also see (among others): "phase" conductor (or "phase" for short), phase referring to a pair of wires from a polyphase circuit, "phase" referring to a voltage in general.

 

[mivey]

The equations you're using are ONLY true when the PHYSICAL transformer is neglected...
Yes, because without the specifics of a transformer, the equations promoted by rattus et al are absolutely correct.

No one is ignoring any physics. You are trying to say there is only one way and it is absolute.

Consider a voltage difference between two points:
Is it more correct to say that one point has an excess of electrons, or that the other point has an excess of protons, or that there is a charge imbalance between the two points? Is it more correct to say there is a rise from a reference to one point, or a fall from a reference to the other point? Taking one viewpoint does not negate the others and make them not a physical reality.

 

[mivey]

On where you can and can't connect ground clips...Luckily, the voltmeter was fused on both sides at 2A. One of them blew, that's all.

Keep your differential probes with you as they come in handy and can keep you out of trouble. Sometimes.

 

[mivey]

Just that opposite polarity , I said from day one a few yrs. back that I don't think
polarity and Phase are the same thing.

Polarity and direction are not the same thing either.

 

[gar]

111121-2329 EST

rattus:

Vacuum tube in the 50s, Philbrick P65 in 62, 709, misc others of that time, 741, 725, OP7. The capability has really improved.

About 1949 a classmate's father was head of research at Ford Hospital. The desire was to build an oxyhemograph (not sure of the spelling, yes it is correct, but spell checker does not think so). This would require a low level DC amplifier. I started work on this but in 50 I went to Colorado, then in the fall quarter got called to active duty in USNR. Never heard what may have resulted. It would have been a chopper from DC to AC, and then rectification, but not synchronous.

.

 

[gar]

111122-1047 EST

Consider a single phase source, a single secondary winding with no taps, and labeled X1 and X2.

Connect two loads.

Load 1 is a series string of one inductor and one resistor, R1. The free end of the inductor connects to X2, and the free end of the resistor to X1.

Load 2 is a series string of one capacitor and one resistor, R2. The free end of the capacitor connects to X2, and the free end of the resistor to X1.

Do the two output voltages, the resistor voltages, constitute a two phase system? If not, then why not?

.

 

[rattus]

111121-1953 EST

What happens when you add two sine waves of equal magnitude together where one sine wave is 180 degrees out of phase with respect to the other?

Get a two input analog adder circuit with equal gain on both inputs. Connect the adder's common to the transformer center tap. Connect one adder input to one end of the secondary, and the other adder input to the other end of the secondary. What is the output of the adder?

.

Not much!

 

[ronaldrc]

Polarity and direction are not the same thing either.

No they aren't they are indicators of the direction of flow, So?

Some use Electron flow and some the conventional flow and they are opposite of each other.
Now less see how complicated you can make that statement.


Why is it there are a few EEs on here that try to trash everything we where ever taught about basic electricity just to make simple tools we use to seem more complex than they really are?

We can't even use a simple equation like ohms law without you always having to drag pf.or
capacitance into it every time we bring it up just to make it more complex.

Sorry about the rant, but my gosh. :rant:

 

[gar]

111122-1303 EST

rattus:

Do you think anybody will say it is double the voltage of one side of the center tap?

.

 

[rattus]

111122-1303 EST

rattus:

Do you think anybody will say it is double the voltage of one side of the center tap?

.

Someone, somewhere, because it is after all, an adder.

BTW, I was taking an analog computer course in 1960 and we used the Philbrook op-amps in the lab. And, about 10 years later someone designed an analog calculator and wanted us to build it. Bad idea.

 

[rattus]

No they aren't they are indicators of the direction of flow, So?

Some use Electron flow and some the conventional flow and they are opposite of each other.
Now less see how complicated you can make that statement.


Why is it there are a few EEs on here that try to trash everything we where ever taught about basic electricity just to make simple tools we use to seem more complex than they really are?

We can't even use a simple equation like ohms law without you always having to drag pf.or
capacitance into it every time we bring it up just to make it more complex.

Sorry about the rant, but my gosh. :rant:

Now simmer down ronald. What you have learned has served you well for 40 years hasn't it? We are just pointing out that there are other ways to look at a problem.

 

[gar]

111122-1436 EST

rattus:

I was working on the development of an electronic circuit breaker in 62 and purchased two of the Philbrick amplifiers and neither worked on receipt. Called them and they guaranteed to me that every unit was tested before shipment. That was nonsense. Sent those back and later received good units. This was not the first or last time that I have been told that products were OK on shipment, but in reality could not have been.

In the early 1970s I was using a dual 22 pin card-edge connector from Cinch. These had been perfectly good until a batch in early 72. Then, with high probability, these were splitting down the middle of the connector back, and thus greatly reducing contact pressure. I tried to convince Cinch these were defective, and they said my boards were too thick. Or I was doing something else wrong. My only solution at that time was to pretest sockets before installation by inserting a board and then bending it back and forth to apply substantial stress on the connector. If it did not fail it was used, otherwise scrapped. About 3 months later Cinch found they had a problem and 100,000 bad units in their warehouse. The problem was in the molding formulation and process. Somewhat after this I ceased using Cinch connectors.

In the 1950s a company, Applied Dynamics, was started in town by the Gilbert brothers to make analog computers. This company still exists and now makes a combination analog and digital computer. The Gilberts were very bright students and professors in the Aero department. Never used one of their computers.

.

 

[ronaldrc]

You're right Rattus but theres to much nitpicken


I mean polarity isn't the same thing as direction
really

 

[pfalcon]

Wow! The things that proliferate while I'm gone.

I want to know the phase angles seen on L1 and L2 of a split phase system! Voltages measured relative to the neutral.

sigh. You're question here presumes the use of an apparent measurement technique. Measured from the neutral the two apparent voltages will be |120 Vac| and 180 degrees out of phase.

Then we must be talking about two different things because I usually aced mine. ... Consider the battery that keeps being used as an example: ...

And if you'd listen to me you'd ace the rest of the exams! Sorry, just had to say that. Ya kinda walked into it.
And no, DC batteries have nothing to do with transformers and are therefore irrelevant to the discussion and I have therefore never used it.

No one is ignoring any physics. You are trying to say there is only one way and it is absolute. ...

Let's try to keep this simple. And I'll type real slow so you can understand :angel:

Without consideration of the primary coil: A.L.L Y.O.U.R E.Q.U.A.T.I.O.N.S A.R.E V.A.L.I.D

So you can stop asking me what I would measure with a meter or a scope. I've never claimed you would measure otherwise under the conditions you've stated. Nor have I ever stated that your equations, based on an equivalent circuit would ever produce an incorrect answer.

What I am claiming, is that if you are creating an equivalent circuit that includs the transformer primary then both secondaries must be marked with the same phase and polarity. Otherwise it doesn't correctly model the transformer.

 

[rattus]

sigh. You're question here presumes the use of an apparent measurement technique. Measured from the neutral the two apparent voltages will be |120 Vac| and 180 degrees out of phase.

What is apparent about scope traces? What you see is what is there!