110V to 220V for mini-split.

[timselectric]

I see where confusion is coming from. The guy in the video is calling 2 transformer windings being in phase but if your were to take a reference point in the middle of them and then measure voltage waveforms at opposite ends in relation to the middle they would look 180 deg out of phase. Too bad he did not demonstrate it with a scope.

Now you've got it.

 

[timselectric]

At 1:31 in the video he explained how split phase works when the lower windings are in opposite direction from the upper windings. He used the term, "out of phase with each other". Earlier at 1:25 he described how both 120volt legs would be in phase if all the windings were in the same direction. In both cases the transformer is center tapped.

Split-phase phase doesn't work unless the two windings are in the same direction. You would only get the two separate 120v sides. If the windings were wound in opposite directions.

I thought the DC battery illustration was confusing because in that example the neutral carried double the current but that is not how it works in a 3 wire shared neutral AC system in North America.

That's what would happen if the windings were wound in the opposite direction.
I know that he said out of phase. (I think that he was trying to simplify it)
But they are actually in phase, but in opposition.
It's single phase, so only one phase exists.
Phasing is just timing. Single phase is one phase.
3 phase is 3 phases separated by time. One third from each other (120deg) around an axis (generator shaft).

 

[Ampster]

Too bad he did not demonstrate it with a scope.

Yes, I watched the entire video and he explained why it looks like split phase because it depends on what reference you use. The windings are in the same direction and I will correct my earlier post.
Also @timselectric clarified it.

 

[ericfx1984]

Maybe I'm missing something here.. But it seems like it would just make sense to use 120 volt mini split in the first place?

 

[timselectric]

Maybe I'm missing something here.. But it seems like it would just make sense to use 120 volt mini split in the first place?

Yup
Simplicity is perfection.

 

[timselectric]

Yes, I watched the entire video and he explained why it looks like split phase because it depends on what reference you use. The windings are in the same direction and I will correct my earlier post.
Also @timselectric clarified it.

This is where the confusion comes from.
90% of the scopes used are non isolated (less expensive).
So the reference lead is internally bonded/ grounded.
On these scopes you have to reference from the neutral. Or you could damage the scope.
So, it looks like two phases 180deg from each other on the screen. And without ever being told that it wasn't. People assume that they are seeing it correctly.
The only way to reference it and view it accurately is with an isolated scope. But they are a lot more expensive. And not worth the additional cost, just to see it correctly on the screen.

 

[AntronX]

Like your video guy said, both concepts are correct depending on your reference point. Calling two waves out of phase by 180 degrees is valid. Seems like electricians are overly dogmatic when it comes to concept of phase probably due to narrow field of view.

 

[Ampster]

both concepts are correct depending on your reference point.

That is helpful. My reference point was a 3 wire circuit with a shared neutral. I assumed that the phases were split in order for that single neutral to carry the loads of both legs. That led me to only a partial understanding and an incomplete way of describing it.
EDIT: I also learned a valuable lesson to watch the entire video to get the correct concept. I pulled a short clip from an early section which fit my pre conceived assumption.

 

[Ampster]

But it seems like it would just make sense to use 120 volt mini split in the first place?

Yes it would except the OP said he could not find one that was top mounted like he needed. That is why the solution of an auto transformer was suggested.

 

[timselectric]

Calling two waves out of phase by 180 degrees is valid.

It's not.
When talking about split-phase.
But it could be if the transformer was wound in opposite halves. But then, it wouldn't be split-phase.

 

[AntronX]

It's not.
When talking about split-phase.
But it could be if the transformer was wound in opposite halves. But then, it wouldn't be split-phase.

When your point of reference is center tap of seconday winding then two waves are out of phase. Phase describes timing relationship between waves. It does not mean only 3 phase is phase valid. Before 3 phase there was 2 phase system 90 degrees apart (out of phase). It was called 2 phase system. Delay the waves by extra 90 degrees and it's still 2 phase but 180 deg a part. All valid.

 

[timselectric]

When your point of reference is center tap of seconday winding then two waves are out of phase. Phase describes timing relationship between waves. It does not mean only 3 phase is phase valid. Before 3 phase there was 2 phase system 90 degrees apart (out of phase). It was called 2 phase system. Delay the waves by extra 90 degrees and it's still 2 phase but 180 deg a part. All valid.

This is all that I will say, then I have to give up.
Phasing is timing. There is only one phase available at the input. So there is only one phase at the output.
If you wound the coils in opposite direction. The current would flow in opposition to each half. But still would be in phase with each other.
Just like he showed in the video, with the batteries with arrows on them. It doesn't matter if they are pointing in the same direction or opposite direction. They still alternate direction in time (phase) with each other.
I hope that that makes sense. I really can't explain it any better than he did in the video. He does a very good job of making things easy to understand.

 

[AntronX]

It makes perfect sense but you keep latching on to what happens upstream at transformer coils. I am telling you to look at this system from voltage POV at the reference point of center tap and forget what is happening upstream. I give up as well. Electricians and electrical engineers will never see eye to eye.

 

[timselectric]

It makes perfect sense but you keep latching on to what happens upstream at transformer coils. I am telling you to look at this system from voltage POV at the reference point of center tap and forget what is happening upstream. I give up as well. Electricians and electrical engineers will never see eye to eye.

You can look at it from any direction you want. (Point of view)
But you can't change physics by looking at it differently.

 

[ksmithaz1]

You are almost grasping this. They try to cancel each other when you connect a load of certain impedance across them. If you were to tie them together you would get them to cancel out creating a short circuit. The only reason current can flow between L1 and L2 is because they are pushing and pulling against each other with each half sine wave cycle.

No they are not. There is one coil with a 240v output. The center tap is incedental. You see them 180 out of phase because you are using the center tap as a reference. Put common on L1 probe on CT probe on L2. . . They are in-phase. ISOLATED probe L1 to CT and ISOLATED probe CT to L2, the bounce at the same interval.