240v debate....

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Rick Christopherson said:
Well, that's pretty much what I've been saying from the beginning........On the same waveform, a phase shift is a time shift. Are you somehow suggesting that with a single-phase, center-tapped, common-core transformer, you are getting two different waveforms on the secondary from a single waveform on the primary? When you change (ῳt) to (ῳt+180), it's either two waveforms or an added time shift. Those two points do not occur at the same point on a waveform.
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Well of course there are two waveforms (just counting the neutral to ungrounded ones) as we have a three-wire circuit.

Rick Christopherson said:
Mathematically it is fine to say that cos(ῳt) = -cos(ῳt+180), but it is wrong to extend this mathematical interpretation into the absolute function of a center-tapped transformer. Yes, it works when you have a pure and perfect sinusoidal waveform, but that does not mean the transformer's function can be defined that way. This is why I have been trying to get you to understand the difference of putting a non-symmetrical wave into the transformer.

It's not that I am obsessed on non-symmetrical waves. I am trying to use that as a means to get you to see than there is a difference between your mathematical model and how the transformer is defined. You can mathematically model the transformer any way you wish, but some members here have made assertions that their mathematical model is absolute, which therefore defines the transformer instead of just modeling it.
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We are not modeling the transformer but we are modeling what leaves the transformer. That is not quite the same thing. Consider the unbalanced case and how the neutral current makes the currents in the two winding halves unequal.
 
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OP:
stickboy1375 said:
I wanted to run a pump at 240v vs 120v, for obvious reasons, voltage drop, wire size, etc. But... I get this a lot from people, 240v is more dangerous. So I'm looking for a better way to explain to people that its just as safe as a 120v circuit but with better benefits.
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Print this thread. It is full of valuable information. I'm sure your customers will understand much better after reading it.:lol:
 
Rick Christopherson said:
It's not that I am obsessed on non-symmetrical waves. I am trying to use that as a means to get you to see than there is a difference between your mathematical model and how the transformer is defined. You can mathematically model the transformer any way you wish, but some members here have made assertions that their mathematical model is absolute, which therefore defines the transformer instead of just modeling it.
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That is just silly. The beauty of mathematics is that it is either true or not. In transformer mathematical models it is stated that there are certain aspects ignored for simplicity sake, since their impact is insiginficant. Could you point out what competing transformer mathematical models are you aware of?
 
Rick Christopherson said:
Well, that's pretty much what I've been saying from the beginning........On the same waveform, a phase shift is a time shift. Are you somehow suggesting that with a single-phase, center-tapped, common-core transformer, you are getting two different waveforms on the secondary from a single waveform on the primary?
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Yes. That's what you get when you use the center tap as the reference point. Maybe your failure to understand this is where you're becoming unstuck

120-0-120Vrev03.jpg


It's a necessary condition for the rectified waveforms to be as they are and as I posted. And you evidently don't dispute that they are as they are.

Rick Christopherson said:
When you change (ῳt) to (ῳt+180), it's either two waveforms or an added time shift. Those two points do not occur at the same point on a waveform.
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At the risk of repetition ad nauseum, it is two different waveforms.

Rick Christopherson said:
Mathematically it is fine to say that cos(ῳt) = -cos(ῳt+180),
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I don't think anyone would dispute that. Question it's relevance to the present discussion, maybe. But dispute it? Probably not.
Rick Christopherson said:
but it is wrong to extend this mathematical interpretation into the absolute function of a center-tapped transformer.
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I don't think anyone here did......correct me if I have missed that.

Rick Christopherson said:
It's not that I am obsessed on non-symmetrical waves. I am trying to use that as a means to get you to see than there is a difference between your mathematical model and how the transformer is defined. You can mathematically model the transformer any way you wish, but some members here have made assertions that their mathematical model is absolute, which therefore defines the transformer instead of just modeling it.
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I, for one, am not modelling anything. Just presenting what you see in real life. Or at least those of us who deal with such real world stuff.

Now, maybe you could answer the questions I asked you in post #109.
 
mivey said:
Well of course there are two waveforms (just counting the neutral to ungrounded ones) as we have a three-wire circuit.
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Is this really your answer? Are you honestly confusing a waveform with a voltage? How can you possibly justify this statement with the previous statement that you made, "On the same waveform, a phase difference is a time difference."? So according to your new rationale, every time you have a new voltage its a different waveform?

mivey said:
We are not modeling the transformer but we are modeling what leaves the transformer. That is not quite the same thing. Consider the unbalanced case and how the neutral current makes the currents in the two winding halves unequal.
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Now all of a sudden we aren't modeling a transformer? We just have 3 wires that miraculously appear? Hey, can we re-label them Tom, Dick, and Hairy then? That would be a lot more interesting.

Great posting Mivey. Really shows your character. If you can't win a debate, just change the rules.
 
weressl said:
That is just silly. The beauty of mathematics is that it is either true or not. In transformer mathematical models it is stated that there are certain aspects ignored for simplicity sake, since their impact is insiginficant. Could you point out what competing transformer mathematical models are you aware of?
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Well, that is exactly what I have been saying. The mathematics are either true or they are not. If your model does not handle the non-symmetrical waveform that I suggested, then it is not a true model. It's a "simplified" model (to use your words) that works 90% of the time, but some members in this thread are putting that model forth as an absolute.
 
Besoeker said:
At the risk of repetition ad nauseum, it is two different waveforms.
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Just because you see them as two pictures on your scope does not make them two waveforms. Using that rationale, a single piece of copper wire would have an infinite number of waveforms as you moved your second probe farther down the length of the wire and recorded an increasing voltage drop.
 
Rick Christopherson said:
Well, that is exactly what I have been saying. The mathematics are either true or they are not. If your model does not handle the non-symmetrical waveform that I suggested, then it is not a true model. It's a "simplified" model (to use your words) that works 90% of the time, but some members in this thread are putting that model forth as an absolute.
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I'll try this again.
What I posted was not based on a mathematical model.
It's what actually happens in real life with real stuff.
 
Rick Christopherson said:
Just because you see them as two pictures on your scope does not make them two waveforms. Using that rationale, a single piece of copper wire would have an infinite number of waveforms as you moved your second probe farther down the length of the wire and recorded an increasing voltage drop.
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Still you don't or won't get t - and I'm now inclined to think the latter.
I gave you the reference points.
Now, can you answer the questions that I posed in #109?
 
Rick Christopherson said:
So according to your new rationale, every time you have a new voltage its a different waveform?
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New to you, not to me. Thanks for at least listening to some of what I'm saying.:D

A voltage is defined between two points/nodes. Use a different pairing of nodes and you have a different voltage, even if the second voltage is equivalent in value to the first voltage. Basic physics, fundamental electrical theory.

Rick Christopherson said:
Now all of a sudden we aren't modeling a transformer?
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I was not modeling one in the past. However, I can model a transformer if you think it will help you understand. I can also tell you that with some unbalanced loading, the voltages V2n and Vn1 at the transformer terminals will not peak at the same time and will not have the same magnitude. It is not really the issue, but it is a fact.
 
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