Electronics > Beginners
How to wire up a 240VAC receptacle
Richard Crowley:
--- Quote from: Spork Schivago on May 19, 2018, 12:03:30 am ---Okay, so, for example, my BGA rework station that runs of 120-0-120 from the mains, the heating elements have only two connections, one going in, one coming out. They operate directly on 240VAC. Somewhere, in the circuit, before the electricity reaches those heating elements, there must be a connection where the two phases connect to produce that 240VAC, right?
--- End quote ---
No. You may be over-analyzing this. The first "phase" (L1) goes to one side of the 240V heating element, and the other "phase" (L2) goes to the other side of the heating element. Simple as that.
The phases "connect" THROUGH the heating element.
--- Quote ---Here, I have always looked at Neutral and Ground as the same, because in my breaker panel, they are. I take it that's not correct though, I should look at them differently.
--- End quote ---
That is completely true. But it has nothing to do with getting 240V from 120-0-120 split-phase.
--- Quote ---If I were to simply rewire the BGA rework station to have 240VAC going down the L1, ground going down the Earth, and Neutral going down the N, then that would be bad, wouldn't it? Because eventually, L1 (240VAC) would be connecting directly to ground.
--- End quote ---
No. 240V exists only BETWEEN L1 and L2 (the two "phases" of "split-phase".)
There is no Neutral here. And Ground is only the safety path to prevent you from being electrocuted, or from setting your house on fire.
james_s:
It may be easier to visualize this as a transformer with a center tapped secondary, which is exactly what this is. Even simpler you can ignore the center tap because if you want 240V the center tap could be floating or not exist and it would look the same to a 240V load. Consider a single secondary producing 240V, you could ground one end of it to have a Euro-style 240V service, or you could leave it completely floating and have a US style 240V feed. The only difference is that in a real US installation there is a center tap which is tied to ground but that is only relevant when you want to draw 120V from one end or the other to neutral/ground.
C:
If you split a apple PIE do you get two Pies?
So how do you get two phases?
AC = alternating current
--- Quote ---An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.[
--- End quote ---
https://en.wikipedia.org/wiki/Alternator
The hands on a analog clock rotate.
Think of the center of clock as 0 Volts
Max Positive Volts is 12 o'clock.
Max Negative Volts is 6 o'clock.
This makes 3 o'clock & 9 o'clock also 0 Volts as Volts is vertical dimension.
Single phase states you have one hand on clock like hour hand.
60 Hz states that the hand is completing 60 rotations a second.
now when you look at the volt rating is states
RMS
RMS = Root mean square
so if you see "240 Volt RMS" the peak voltage is 1.414 x 240.
So the 12 o'clock position the max positive = 339.36 volts.
You use the sin table to compute a value based on rotation.
With one end at center you 0 volt connection.
As the hand rotates the other end goes from 12 o'clock around to 6 o'clock and back to 12 o'clock.
So single phase 240 volts is like hour hand rotating.
Going from 9 o'clock (0 volts) to 12 o'clock ( +339.36 volts) and around to 6 o'clock (-339.36 volts) and back to 9 o'clock.
Note that the hand is over 1/2 of the clock so the clock face is 678.72 volts in hight.
Split-phase is extending the hour hand to other side of circle. When one end of the hand is at 12 o'clock the outer end is at 6 o'clock.
You have three connections. The two hand tips and the center.
Using full clock face you have the clock face 339.36 volts in hight.
Max Positive (12 o'clock) = +169.68 volts
169.68 / 1.414 = 120 volts RMS
Three phase is 3 hour hands 60 degrees apart.
The center of the clock face is the Neutral connecting in above.
The Hour hand tip(s) are the other connection.
Monkeh posted a plot of the voltage vs time which is also a plot of voltage vs rotation.
Have you used a two cell flash light?
The light connects to the two ends of the batteries in series.
Split-phase is adding a connection between the two batteries.
Get out your pencil and paper and make some drawings.
C
Spork Schivago:
--- Quote from: Richard Crowley on May 19, 2018, 01:13:15 am ---
--- Quote from: Spork Schivago on May 19, 2018, 12:03:30 am ---Okay, so, for example, my BGA rework station that runs of 120-0-120 from the mains, the heating elements have only two connections, one going in, one coming out. They operate directly on 240VAC. Somewhere, in the circuit, before the electricity reaches those heating elements, there must be a connection where the two phases connect to produce that 240VAC, right?
--- End quote ---
No. You may be over-analyzing this. The first "phase" (L1) goes to one side of the 240V heating element, and the other "phase" (L2) goes to the other side of the heating element. Simple as that.
The phases "connect" THROUGH the heating element.
--- Quote ---Here, I have always looked at Neutral and Ground as the same, because in my breaker panel, they are. I take it that's not correct though, I should look at them differently.
--- End quote ---
That is completely true. But it has nothing to do with getting 240V from 120-0-120 split-phase.
--- Quote ---If I were to simply rewire the BGA rework station to have 240VAC going down the L1, ground going down the Earth, and Neutral going down the N, then that would be bad, wouldn't it? Because eventually, L1 (240VAC) would be connecting directly to ground.
--- End quote ---
No. 240V exists only BETWEEN L1 and L2 (the two "phases" of "split-phase".)
There is no Neutral here. And Ground is only the safety path to prevent you from being electrocuted, or from setting your house on fire.
--- End quote ---
I'm trying to learn, that's why I asked about the Neutral and Ground. So if L1 and L2 are going into the heating element, where is the completed path? Where does it go back to Ground? Electrons are attracted to electrons of the opposite charge, right? So if I feed a heating element just two 120VAC sources, I wouldn't think it'd heat at all....that's where I'm getting confused here. I was always taught you need a complete circuit, and without it, you don't get a working circuit. Each load draws current and has a voltage drop. By the time we get to ground, that voltage is 0VDC. But without that ground, where do the electrons go? Just L1's electrons fly down L2's conducting material and L2's electrons fly down L1's conducting material, even though they're of the same charge? Or is it because they're not in phase, this works? If L1 is out of phase with L2, then L1 would be the opposite charge of L2?
Spork Schivago:
--- Quote from: C on May 19, 2018, 01:47:57 am ---
If you split a apple PIE do you get two Pies?
So how do you get two phases?
AC = alternating current
--- Quote ---An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.[
--- End quote ---
https://en.wikipedia.org/wiki/Alternator
The hands on a analog clock rotate.
Think of the center of clock as 0 Volts
Max Positive Volts is 12 o'clock.
Max Negative Volts is 6 o'clock.
This makes 3 o'clock & 9 o'clock also 0 Volts as Volts is vertical dimension.
Single phase states you have one hand on clock like hour hand.
60 Hz states that the hand is completing 60 rotations a second.
now when you look at the volt rating is states
RMS
RMS = Root mean square
so if you see "240 Volt RMS" the peak voltage is 1.414 x 240.
So the 12 o'clock position the max positive = 339.36 volts.
You use the sin table to compute a value based on rotation.
With one end at center you 0 volt connection.
As the hand rotates the other end goes from 12 o'clock around to 6 o'clock and back to 12 o'clock.
So single phase 240 volts is like hour hand rotating.
Going from 9 o'clock (0 volts) to 12 o'clock ( +339.36 volts) and around to 6 o'clock (-339.36 volts) and back to 9 o'clock.
Note that the hand is over 1/2 of the clock so the clock face is 678.72 volts in hight.
Split-phase is extending the hour hand to other side of circle. When one end of the hand is at 12 o'clock the outer end is at 6 o'clock.
You have three connections. The two hand tips and the center.
Using full clock face you have the clock face 339.36 volts in hight.
Max Positive (12 o'clock) = +169.68 volts
169.68 / 1.414 = 120 volts RMS
Three phase is 3 hour hands 60 degrees apart.
The center of the clock face is the Neutral connecting in above.
The Hour hand tip(s) are the other connection.
Monkeh posted a plot of the voltage vs time which is also a plot of voltage vs rotation.
Have you used a two cell flash light?
The light connects to the two ends of the batteries in series.
Split-phase is adding a connection between the two batteries.
Get out your pencil and paper and make some drawings.
C
--- End quote ---
With those batteries though, that connection between them has to return back to either the bottom cell or the top cell to complete the circuit, otherwise, the electrons have no place to go. That's what I don't understand with the AC, unless I was right about the L1 and L2 being opposite charges, one being +120VAC, the other being -120VAC, and the +120VAC passes through the heating element to the -120VAC, providing a voltage drop of 240VAC total over the heating element....is that correct?
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