240v debate....

[Rick Christopherson]

Wow. All that for some phantom time shift that only you argued was occurring. What a let down.

Umm David, I was the one arguing that the phantom time shift didn't exist. Everyone else has been arguing that there exists a 180 degree shift. I mean no offense by this, but that's why I commented about your comprehension of what was said previously in this thread.

 

[readydave8]

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.

I'm too tired to read 180 posts, what was the short answer?

 

[ActionDave]

The short answer is 240V is not more dangerous than 120V because either is capable of giving a lethal shock and the voltage to ground (which is the most likely accidental shock) is the same.

 

[jumper]

I'm too tired to read 180 posts, what was the short answer?

42

 

[Besoeker]

Umm David, I was the one arguing that the phantom time shift didn't exist.

Well, that's pretty much what I've been saying from the beginning........On the same waveform, a phase shift is a time shift.

Your words from a few posts back.

Just because you see them as two pictures on your scope does not make them two waveforms

Also your words. And just plain wrong.

Here's a thought for you. What is the transformer centre tap wasn't actually at the centre? Say the 120-0-120 was 180-0-60 for example. (You'd still get 240V from end to end, of course.)I'm sure you can see that would give you two different waveforms WRT to the tapping point:

If you can see that, why would you continue refute that the 120-0-120 gives two different waveforms?
None of the above is based on any model of any kind. It is what actually happens in the real world.
And I note that you still didn't answer the questions I posed in post #109.

 

[hurk27]

I'm too tired to read 180 posts, what was the short answer?

the North Pole shifted 90? to the right so down is 90? left is 180? and up is 270? leaving 0? to the right, and poler notation is as confusing as rectangle notation and if your spice comes out right your a winner, and the world is no longer round:slaphead:

 

[hurk27]

Your words from a few posts back.


Also your words. And just plain wrong.

Here's a thought for you. What is the transformer centre tap wasn't actually at the centre? Say the 120-0-120 was 180-0-60 for example. (You'd still get 240V from end to end, of course.)I'm sure you can see that would give you two different waveforms WRT to the tapping point:

If you can see that, why would you continue refute that the 120-0-120 gives two different waveforms?
None of the above is based on any model of any kind. It is what actually happens in the real world.
And I note that you still didn't answer the questions I posed in post #109.

Been a while since I have got my Tectonics quad trace out, but if I remember right, to take readings from a center tapped transformer one would have to reverse the anode and cathode on the second V2-N measurement points or the cathodes would short out since they are common between each BNC input, then use the phase reversal switch to swap what the real wave should look like? if that is the case here then these two waves would be in sync but at different amplitudes?

Two have two series windings with one reversed will be subtractive instead to additive which in the above would be 120 volts not 240 end to end?

 

[mivey]

Wow. All that for some phantom time shift that only you argued was occurring. What a let down.

Kind of like someone who grabs the ball, runs onto the field and trips on his own shoelace, assess himself a penalty for personal foul, then marches into the end zone and spikes the football, declaring victory.

 

[mivey]

Been a while since I have got my Tectonics quad trace out, but if I remember right, to take readings from a center tapped transformer one would have to reverse the anode and cathode on the second V2-N measurement points or the cathodes would short out since they are common between each BNC input, then use the phase reversal switch to swap what the real wave should look like?

If by "real" you mean the real V2n and Vn1 voltages, then correct. You could also use isolation transformers. But you do not have to do that for the real V2n and V1n voltages. BTW, both sets of voltages are real.


Instead of using leads like this:

....Red1.....Red2
.....)........)
.....)........)
.....)........)
-----------------ground plane-Black

You want to use them like this:

...Black1......Red2
.......)........)
.......)........)
...Red1)........)Black2
------------------ground plane

Both both are valid and measure valid, real voltages

 

[david luchini]

Kind of like someone who grabs the ball, runs onto the field and trips on his own shoelace, assess himself a penalty for personal foul, then marches into the end zone and spikes the football, declaring victory.

Amen to that. I was expecting something better than: Doc Brown threw Vbn into the Delorean and drove it 8.3ms into the future.....and since that can't REALLY happen...

 

[Rick Christopherson]

At this point, maybe it would be a good idea to step back for a second and reaffirm what is being discussed and what is not. Let's start with the following re-quote:

Umm David, I was the one arguing that the phantom time shift didn't exist.

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.

Your words from a few posts back.

Apparently Besoeker and David Luchini took these comments to be contradictory with each other. So I will re-explain what these statements mean.

#1, I am asserting that a phase shift is a time shift. #2, I am asserting that because we know that you cannot have a time shift in a single phase transformer (as David has now affirmed regarding my non-symmetry example) then you cannot have a phase shift in a single phase transformer. Whether you agree or disagree with the assertions, is what is being discussed, but I have not wavered from them.

What's NOT being argued: Some people have a personal preference of designating the center-tap (neutral) as a common voltage reference. This is a personal preference, and as such, it cannot be argued. What may be leading to some needless confusion is that I suspect that some people might be asserting their personal preference as though it was mandatory for everyone to follow.

Even though I do not make the choice to use the neutral as a common reference, I also do not try to force this choice on anyone else. That would be like trying to tell someone what their favorite color should be.

What IS being argued: Some people that choose the personal preference of using the neutral as a common voltage reference point have extended this choice to also mandate a 180? phase shift as part of their choice. Instead of acknowledging that their choice is just a polarity change, they are redefining the system to include a 180? phase shift that does not exist.

It is technically correct to say that V_1n = -V_n1, but it is not technically correct to say that V_1n<0?= V_n1<180?. To say the latter introduces a time shift into the signal that does not exist.

Caveat: For the purposes of analysis, it can be acceptable to use V_1n<0?= V_n1<180?. However, where this steps over the line is when a person states that V_1n<0?= V_n1<180? is actual and real. My example of the non-symmetrical waveform proves that this condition is neither actual, nor real.

 

[iwire]

Unbelievable. :lol:

 

[Rick Christopherson]

Unbelievable. :lol:

And this from someone that isn't even qualified to contribute to the discussion? :dunce:

How's that for condescension?

 

[jumper]

And this from someone that isn't even qualified to contribute to the discussion? :dunce:

How's that for condescension?

I am certainly not qualified, but I have a AS in Electronics and a Certificate in Applied Electricity that both transfer to an EE program, so I can follow along. You are getting chewed up in this thread. Dave, Mac, Mivey, and Lazlo have all refuted your position.

I am stubborn as heck, but I know when to

 

[Besoeker]

Been a while since I have got my Tectonics quad trace out, but if I remember right, to take readings from a center tapped transformer one would have to reverse the anode and cathode on the second V2-N measurement points or the cathodes would short out since they are common between each BNC input, then use the phase reversal switch to swap what the real wave should look like? if that is the case here then these two waves would be in sync but at different amplitudes?

Anode and cathode on scope leads....think you lost the plot there.
If you want to measure the the two voltages to neutral on a centre tapped transformer you need a dual trace oscilloscope. You would have have a common point to which you would connect ONE of the grounded leads. And measure and display both with respect to that.

Two have two series windings with one reversed

Neither is reversed.
Maybe that's where you are getting your knickers in a twist.

 

[jwelectric]

During this entire thread I don?t believe that there is more than one person that knows what they are talking about and I quit talking which leaves none.

Unbelievable.

I agree

 

[iwire]

And this from someone that isn't even qualified to contribute to the discussion?

You are right, I am not qualified to comment on the electrical discussion here.

But I am more than qualified to recognize a man making a fool of himself. :thumbsup:

 

[Besoeker]

I am asserting that a phase shift is a time shift.

Nobody is disputing that.

I am asserting that because we know that you cannot have a time shift in a single phase transformer (as David has now affirmed regarding my non-symmetry example) then you cannot have a phase shift in a single phase transformer.

Nobody is asserting that you can.

Some people have a personal preference of designating the center-tap (neutral) as a common voltage reference.

Personal? I think not. If you want to compare the two 120V sections you need to have a common point. There are just three terminals. You are correct in saying that you could use any one as a common point. If you use either end as a common point then you would not be comparing the two 120V sections of the winding. Don't you see that?

Some people that choose the personal preference of using the neutral as a common voltage reference point have extended this choice to also mandate a 180? phase shift as part of their choice. Instead of acknowledging that their choice is just a polarity change, they are redefining the system to include a 180? phase shift that does not exist.

Again, you don't seem to understand. Or won't.
There is no phase shifting going on. The two 120V outputs are 180deg apart. Were it not so, you wouldn't have 240V end to end on the transformer.
Can't you see that?

 

[Lady Engineer]

You are right, I am not qualified to comment on the electrical discussion here.

But I am more than qualified to recognize a man making a fool of himself. :thumbsup:

Ouch, iwire, you were bitten!!

I guess I should join in the conversation, because I'm a "PE" and so I'm qualified? I'm just joking guys...really.

Honestly, this was on my PE exam. I was very good at it when I took the PE, but now that I deal with Medium Voltage, I don't remember as much. Basically, it's a refresher, and I'm ok with that.

Carry on...

 

[jim dungar]

If you want to compare the two 120V sections you need to have a common point.

Just because your scope is limited in its connections, (it forces you to use the neutral as a common) you see something that appears as a 'phase shift' or an 'inversion' of two waves.
Use a different scope arrangement so that you can measure V1n and Vn2.

When I was taught KVL, I would have written the loop formula as V12=V1n+Vn2, which IMO 'looks correct' even if there is no circuit connection from 'n' back to the center point of the source. My professor would have had a conniption, if I had written this simple loop as V12=V1n-V2n, even if it is mathematically equal.