240v split phase correction

does split-phase have 2 sine waves in phase or out of phase with each other


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Reloadron

Joined Jan 15, 2015
7,501
You can't measure voltage PHASE TO PHASE on a scope like that.
Yes you can depending on the scope. First use neutral (which is the transformer center tap) and using a simple dual channel scope measure each side of the transformer. You will see two sine waves 180 degrees apart. So actually if I add the two channels, which most scopes allow I will see a flat line since algebraically adding two channels of the same amplitude which are 180 degrees apart and of the same amplitude will equal zero. However, if using my scope I invert channel two I will see the sum of both wave forms.

This is also easily done using a scope and differential probes but the method I just mentioned works fine. Again this will be a matter of the scope you are using and the features. My example is based on an old Tektronix 2235 100 MHz analog old scope so nothing new.It is just a matter of manipulating the channels.

Ron
 

dendad

Joined Feb 20, 2016
4,451
Just a quick final note, the in phase or 180 degrees out of phase wiring of the secondaries also depends on if you are hooking them up for series or parallel use too.
Even tho the actual winding phase doesn't change, it is just the way we refer to it.
Just a bit more mud for the water ;)
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
The two windings in the original question are in phase, like 2 batteries in series. But like in the battery example, if you measure from the centre tap you will get + and - voltages, or 2 phases 180 degrees different. But the windings ARE in phase. The confusion stems from the reference point being the centre, not one end.
For example, it is a common trick to add a low voltage secondary winding of a transformer either in phase or out of phase in series with the mains to increase or decrease the mains volts a bit.
So the windings are in phase, but not the voltages.
I can not compute.
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
The two windings in the original question are in phase, like 2 batteries in series. But like in the battery example, if you measure from the centre tap you will get + and - voltages, or 2 phases 180 degrees different. But the windings ARE in phase. The confusion stems from the reference point being the centre, not one end.
For example, it is a common trick to add a low voltage secondary winding of a transformer either in phase or out of phase in series with the mains to increase or decrease the mains volts a bit.
" if you measure from the centre tap you will get + and - voltages, or 2 phases 180 degrees different. "

what would the voltage be.
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
Same as UK, whether using a phase to a phase, or a phase to the star neutral, they are each Single Phase.
Max.
Sure you (carefully) can if the scope is isolated from neutral/ground with internal battery power or by using a isolation transformer. You need to separate the circuit (split-phase voltage from the center-tap) from the transformer voltage source physical component. If you were tasked with repairing (in an emergency like Harvey) a utility circuit using two bad utility step-down transformers transformers, each transformer had one end from the center tap to output secondary open but the opposite side from center-tap to output was good. How would you phase the output connections to make it deliver a correct 240VAC output to a split-phase circuit in a home?
I don't know, sounds like you do.
But whatever, fine, I guess you can measure from phase to phase.
 

nsaspook

Joined Aug 27, 2009
13,079
I don't know, sounds like you do.
But whatever, fine, I guess you can measure from phase to phase.
I understand your confusion because some of that single-phase article is confusing. When people say 180 out of phase from split-phase neutral they are correct, when people say the transformer source voltages are in phase they are also correct because it's about separate parts of a system that consists of AC voltage sources (typically transformer(s) with coils and connections (internal or external), a circuit (split-phase or single-phase) wiring connected to those transformer connections and possible loads on those circuits.
 
Last edited:

crutschow

Joined Mar 14, 2008
34,280
Here's a simulation to show the phase voltages (V1 and V2 simulate the center-tap transformer output):
This is what you would see with an oscilloscope.

The 120Vrms output A (Green) is 180° out-of-phase with output B (Yellow), both measured to Neutral.

There is then 240Vrms measured between A and B (Red).
The 240V could be measured by using the two oscilloscope inputs in a differential mode (one input set to invert and the two inputs summed) with oscilloscope common to Neutral.
(That, of course, ignores the hazards of actually doing such measurements. :eek:)

upload_2017-9-3_9-40-39.png
 

BR-549

Joined Sep 22, 2013
4,928
Mac.......It it very apparent that you do not understand the concept of "reference" for measurement or circuit operation. This will get you or others injured and burn up equipment.

Your thread question has been answered thoroughly. Stick to low... ~12 volt DC & AC circuits until you gain understanding.

Use a fused 120 to 12 v center tap transformer to study AC(stay away from primary side)..........before fooling around with line voltages. This will give you two 6 VAC "out of phase" legs. Study and practice scope/measurement isolation at these voltages.

Please review the concepts of potential......and the need for a reference. The concept of phase.....also has to have a reference.

Many circuits change these references during circuit operation. We can manipulate the current this way.

You need to know this to take measurements. Even if there was no danger in connecting to the wrong reference.......the measurement would not be correct......it would be false. You would be wasting your time.
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
I understand your confusion because some of that single-phase article is confusing. When people say 180 out of phase from split-phase neutral they are correct, when people say the transformer source voltages are in phase they are also correct because it's about separate parts of a system that consists of AC voltage sources (typically transformer(s) with coils and connections (internal or external), a circuit (split-phase or single-phase) wiring connected to those transformer connections and possible loads on those circuits.
" some of that single-phase article is confusing.."
that is an understatement
 

Thread Starter

Mac Rodriguez

Joined Mar 24, 2016
140
Mac.......It it very apparent that you do not understand the concept of "reference" for measurement or circuit operation. This will get you or others injured and burn up equipment.

Your thread question has been answered thoroughly. Stick to low... ~12 volt DC & AC circuits until you gain understanding.

Use a fused 120 to 12 v center tap transformer to study AC(stay away from primary side)..........before fooling around with line voltages. This will give you two 6 VAC "out of phase" legs. Study and practice scope/measurement isolation at these voltages.

Please review the concepts of potential......and the need for a reference. The concept of phase.....also has to have a reference.

Many circuits change these references during circuit operation. We can manipulate the current this way.

You need to know this to take measurements. Even if there was no danger in connecting to the wrong reference.......the measurement would not be correct......it would be false. You would be wasting your time.

This has more to do with correct definition than understanding.
 
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