Hello To All!

I hope you all don't mind that this isn't an electronics question, but more of an electrical engineering question.

I have a portable, single phase generator. The control panel has two output choices: 120 Volts Only or 120/240 volts.
In the owner's manual it states that in 120 volt only mode all of the 120 volt devices (NEMA 5-20R & NEMA L5-30) are using the "full output power of the alternator". It further states that in 120/240 volt mode, only half of the alternator's output power is available at the 120 volt devices, with the other half at the 120/240 volt device (NEMA L14-30R).

Testing with a volt meter shows that in both 120 Only and 120/240 Modes, the 120 volt devices are indeed on the same phase. Also on that phase is half of the 120/240 device. The other half of the device is not powered in this mode (as expected).

In 120/240 volt mode, the 120 volt devices are still on the same phase, along with half of the 120/240 volt device. The other half of the 120/240 volt device is, as expected, on the other phase.

To me, this means that in 120/240 Volt Mode, one stator winding supplies "phase a" and one supplies "phase b". But how does the alternator supply all of the alternator's output to the 120 volt devices in 120 Volt Only mode? Surely the windings, which are 180-degrees apart, can't suddenly be in phase by the flip of a switch.

When I tested in 120 Only mode I expected that some of the 120 volt devices would be moved to "phase b", but the meter shows that this is not the case. I studied the wiring diagram for hours, left and came back. Still, I can't figure out the magic. (To be honest, I'm old enough that my brain isn't as logical as it once was, so there's an "old guy" factor involved.)

Attached is the wiring diagram. Can any of you help me understand how the second half of the alternator's output is made available to the 120 devices in 120 Volt Only mode?

I very much appreciate the help and education.

Thanks Again & Please Enjoy This Day!
Paul

 

It looks like the alternator has two 120 volt windings. In 120 volt mode the windings are connected in parallel. In 120/240 volt mode the windings are connected in series. So if the windings are capable of providing a current of 10 amps when they are connected in parallel. 20 amps is available. when they are connected in series the sum of the loads on the 120 volt and 240 volt outputs should not exceed 10 amps.

Les.

 

What is it that You are trying to accomplish ?
You can not increase the Output-Current of your Generator.
The manufacturer already figured out how to get the most out of it.
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Thank You Les & LowQCab for taking time to reply. I very much appreciate your help.

Please be assured that I'm not trying to get more power from the alternator. The original owner already did that by eliminating over-current protection. Thankfully I bought it, disassembled & cleaned it before the varnish on the windings or the windings themselves were burned. (And I put the over-current protection back on line.) Then there were the cooked conductors & the engine damage to deal with... (But I bought it for a very low price because, per the owner: "It smells funny & burns oil.".) It was a rather fun project and learning experience.

My poorly phrased question was trying to figure out how the alternator allows all of its power to the 120 volt circuits when in 120 volt only mode (and half on each phase in 120/240 volt mode.)

Les's explanation really explained things well. Right now I'm having a bad-brain day, but as soon as this neurological event passes I'll dive back into the wiring diagram to follow Les's explanation.

Thanks Again To You Both!
Paul

 

The two windings are NOT different phases. They are in phase with each other. If they were not in phase you could not connect them in parallel. You could think of them as two identical windings on a transformer.

Les.

 

Thank You Les for sticking with me as I try to understand the phasing.
Since the two windings are in phase, how does the alternator produce 240 volts? I guess my skull is thick on this one.

I learned, perhaps incorrectly, that the only way a single phase transformer could produce 240 volts and 120 volts from line to center of a winding was to have the "line" sides 180 degrees out of phase.

Attached is a quick drawing of what I think you are explaining about the phasing.
In the left drawing, are A and B 180 degrees apart? What is the phase angle from A to N or B to N? In the right drawing, what is the phase angle between A and G?
My terminology is probably not correct when I said "phase angle". What I'm trying to say is, on a sine wave, when A is above the zero line, "B" is equal distance below the zero line.

 

Using your diagram I will add some letters X and Y to identify the ends of the unlabeled ends. starting with the right hand drawing. We will leave the ends of the top winding called G and A. We will call the left hand end of the lower X and the right hand end Y. We will assume you have them in phase. We will consider an instant in time when the right hand ends are at the top of the positive leak of the sine wave with respect to the negative ends. So A is positive with respect to G and Y is positive with respect to X. So to the left hand drawing A will be positive with respect to G. For the right hand winding X is the end that was connected to G and Y was the end connected to A. We have to disconnect X from G and connect Y to G and X becomes point B on your left hand diagram so the voltages add. (You could think of the windings a to batteries for this instant in time.) If we had not swapped the end of the XY winding That was connected to point G the voltages would subtract so there would be zero volts between A and B.
I hope that explains it. If you follow the wiring in the diagram in the first post you will see that the voltage selection switch does the series / parallel switching.

Les.

 

There is no real need to think of this problem in terms of degrees,
because the windings are never anything other than zero or 180-degrees apart.

Forget about "AC-Current" for a minute.
Think of the Windings as being Batteries with a Plus and Minus connection.

When You connect the windings in Parallel with each other,
the Voltage does not change, but the amount of Current available has now doubled.

When You connect the Windings in series with each other,
the Voltage Doubles, but the Current is only as much as 1-Battery can deliver.

In either configuration, the available Wattage is exactly the same .........
One of Ohms-Laws ...........Volts X Amps = Watts.
So You can have half the Voltage and twice the Amps, or
Twice the Voltage and half the Amps.
There's no "Free-Lunch".

If You connect the Batteries in series, but reverse the polarity of one of the Batteries,
You get zero-Volts, and therefore, no possibility of any Current flow,
because they are pushing in opposite directions.

If You connect the Batteries in parallel,
and then reverse the polarity of one of the Batteries,
You have now created a loop, better known as a "Short-Circuit", with no Resistance,
and the batteries will supply all the Current that they can generate into each other,
this will result in over-heating the Batteries and possibly a Fire,
and zero useful Output.

In a "Single-Phase" AC System, (which is what You have),
think of reversing the polarity of both Batteries at the exact same time,
and then do that 60 times every second.
This is regardless of whether the Batteries are connected in series or parallel.

A Winding in a Generator, or a Winding in a Transformer,
both sort-of "act-like" Batteries that are being flipped-over 60 times per second.
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Thank You Both Once Again!

I apologize that I haven't replied for days. We have had no electric power nor internet at home for a few days again (ironic, isn't it?).

From your explanations, I think I understand. The analogies of battery and of transformer very much helped.

Attached is a revised drawing of how I think Les explained it. (I apologize, but my aging brain has trouble.)
Armed with Les' & LowQCab's information, I re-visited the schematic. It was much clearer. But, I'm still not positive that I have things correct in my scramble-brain.

In the new drawing, on the right side, G and L are where the 120 volt wiring devices are attached. I read 117 vac across G & L at each device.
On the left drawing, the 120/240 volt device is attached as follows: On the line side is attached to "A", one to "X". The "neutral" is connected to "G" in the drawing. (G and the frame are bonded downstream, so the Ground terminal is electrically also connected to "G".)

I think my confusion lies in the fact that I can read across (left drawing) "A" & "X" and get nominal 240 volts. To my brain, this says they are on different phases. Do I understand correctly that the phase is the same for both, but A is positive with respect to Zero Volts while B is negative?

Also note that the voltages are different when reading from each to "G". I only can assume that there is a slight differencfe in winding efficiency or there is a poor connection somewhere.

Thanks again for helping me learn. Any day when one can learn something new is always a good day!

Paul

 

Your new diagram gives no indication on the left hand (240 volt) configuration of the phasing of the winding that was at the top in the right hand diagram. The end of winding Y is connected to G ( G is for ground it is not a label to identify the end of a winding.)
The winding end L is also connected to G. The other end of that winding (Which had no label in the right hand diagram.) is now labeled A. It would have been clearer if in the right hand diagram if you had labeled the left hand end of the top winding A.
And in the left hand diagram labeled the right hand end of the left winding as L with the left hand end of the right hand winding as Y There would then have bean consistency between the two diagrams.

Les.

 

Sorry that my drawing wasn't done correctly or clearly. Your way is much more clear.
I think my problem understanding is that, since I'm a retired industrial electrician, I was thinking about it in "electrician terms", not electrical engineering or physics terms.

Anytime two conductors have different polarities at a given instant in time, we colloquially call them separate phases. (To better explain- When one is positive with respect to zero volts and one is negative with respect to zero volts, we call them as being separate phases.)
From this discussion, I think I understand correctly that in my generator's alternator, the windings are the same phase, but simply different polarities when connected in series.

For three-phase systems, we call each winding that is 120 degrees apart from another as being a separate phase. I think I'm correct on this one.

To Illustrate What I'm Trying To Explain (trying...)
Attached is a drawing of the secondary side of a transformer. It's here to represent the two stator windings in the generator's alternator.

In the right side of the drawing, am I correct that the winding with X-1 & X-2 leads is the same phase, but opposite polarity as the winding with X-3 & X-4 leads? (The polarity part I've always known, but my apparent misuse of the word "phase" is where I went wonky.)

We goof up a lot of electrical terms, driving the engineers crazy.
Electricians tend to misuse the word "Generator" when referring to the alternator part of a generator. Generators generate DC and Alternators generate AC. But, is suppose since the whole machine is generating electromotive force, the machine is a generator.
One we never mess up is "engine" versus "motor".

Thanks Again for helping me understand. You guys are very good teachers!
Paul

PS:
Just to confuse things, there's the old two-phase system where the phases were 1/4 cycle apart. I'm old enough to have worked on some buildings in Detroit that still had this system for motor driven equipment. They tapped Detroit Edison Company steam to spin a turbine. The more "modern" ones got upgraded to DC. Many still use DC for larger motors, such as elevators, stage lifts, steam pumps, etc.