Trying to understand the sub panel and how 120/240v work

ksmithaz1 · Jul 18, 2023

1201 said:
Nope the oscilloscope doesn't lie.

But if you hook up one side of the scope backwards it will display backwards, ie 180 out of phase. L1-T-L2 your using T as a common but it isn't it's a TAP on a transformer you catch the wave 1/2 way measure L1-L2 then L1-T Two humps one larger than the other, same L1-L2, T-L2, Two humps one larger. The waves are all in phase relative to the input wave. The confusion is around the center tap on the transformer, and using it as the common endpoint. If you do that your probe is measuring the voltage backwards in one direction.

ksmithaz1 · Jul 18, 2023

timselectric said:
For clarification.
That would be split-phase, not two phase.

Split, as in I 'split' the wave 1/2 way thru the cycle with a tap in the middle of the winding. This does not create another phase, you simply get a new reference point 1/2 way with 1/2 the voltage of your phase.

Pappion · Jul 18, 2023

1201 said:
So you're saying the two inverters sync up and create one single sine wave. So how do they create 180 degrees out of phase with respect to neutral if there is no transformer to tap the center of?

The magic of electronic communication between the two inverters keeps them in sync. It is easily possible to do 3 phase also. The inverters must be built for this capability.

Pappion · Jul 18, 2023

I did some digging and there is an legacy 2 phase with 90deg phase. Primarily used with AC motors and it also sets the rotation direction.
I can understand why "Split Phase" was used to avoid confusion. However, Split Phase is technically 2 phase 180deg. Two sets of transformer windings are two sources that can power 2 independent sets of loads. By having a center tap connection it allows them to work together and deliver twice the voltage.
For the sake of communication it's better to use the term the electrical industry uses.

Hedges · Jul 18, 2023

ksmithaz1 said:
But if you hook up one side of the scope backwards it will display backwards, ie 180 out of phase.

I challenge you to try actually hooking a scope up to the AC power line that way.

(do let us know exact model of oscilloscope you did it with.)

Daddy Tanuki · Jul 18, 2023

timselectric said:
Passing on misinformation doesn't help anyone.

then why does the magnum inverter specify that they are 180 apart and that attempting to run two three phase legs into the inverter from a genset will not work as the legs from the three phase genset are 120 deg apart... not saying you are wrong, but magnum made a lot of money for alot of years by being correct....

Pappion · Jul 19, 2023

Hedges said:
I challenge you to try actually hooking a scope up to the AC power line that way.

(do let us know exact model of oscilloscope you did it with.)

Scopes don't float very well, even with a plugs ground removed. Better to use 2 probes.

timselectric · Jul 19, 2023

1201 said:
So you're saying the two inverters sync up and create one single sine wave.

Correct

1201 said:
So how do they create 180 degrees out of phase with respect to neutral if there is no transformer to tap the center of?

They are not 180deg out of phase. It's single phase.
The center tap is between the two inverters. Just like it is between the two coil halves of a transformer.

khisanthax · Jul 19, 2023

Okay, I'm looking at this Inverter. It supports 220-230v but it looks like the AC input only uses L1,N and G. This should still work safely?

timselectric · Jul 19, 2023

ksmithaz1 said:
Split, as in I 'split' the wave 1/2 way thru the cycle with a tap in the middle of the winding. This does not create another phase, you simply get a new reference point 1/2 way with 1/2 the voltage of your phase.

Correct.
Split-phase is a single phase that is split into two halves by the center tap. It's purpose is to provide two different voltages from a single source.

timselectric · Jul 19, 2023

khisanthax said:
Okay, I'm looking at this Inverter. It supports 220-230v but it looks like the AC input only uses L1,N and G. This should still work safely?

That link is for a 120v unit.

Supervstech · Jul 19, 2023

timselectric · Jul 19, 2023

Daddy Tanuki said:
then why does the magnum inverter specify that they are 180 apart and that attempting to run two three phase legs into the inverter from a genset will not work as the legs from the three phase genset are 120 deg apart... not saying you are wrong, but magnum made a lot of money for alot of years by being correct....

I'm not sure where they got that information but it's not correct. Two legs of a 3-phase generator is only one of the phases. (Single phase)
If the voltage is correct, it will work fine. Unless there are bonding differences.
3-phase is just 3 Single phases. The phasing is just time shifting. Each phase is shifted 120 degrees from each other.

timselectric · Jul 19, 2023

Supervstech said:

Thanks
I have posted that video so many times.
I sometimes forget that the new people may have not seen it.

khisanthax · Jul 19, 2023

This one. Sorry I pasted the wrong link somehow and I'll take a look at the video asap.

1201 · Jul 19, 2023

khisanthax said:
This one. Sorry I pasted the wrong link somehow and I'll take a look at the video asap.

That's 240v only so you'll need a transformer for 120v

khisanthax · Jul 19, 2023

1201 said:
That's 240v only so you'll need a transformer for 120v

Right, after watching the video that inverter isn't splitting the phase, only providing 240v, I need something that gives 2 120v or 240v split. Or, as previously mentioned get a separate box for my 240v load?

khisanthax · Jul 19, 2023

So, my options are to get a 220/240v inverter with a transformer that splits the phase or get an inverter like This that already splits the phase, or get a 120v inverter that can be put in parallel and buy 2 of those.

1201 · Jul 19, 2023

khisanthax said:
So, my options are to get a 220/240v inverter with a transformer that splits the phase or get an inverter like This that already splits the phase, or get a 120v inverter that can be put in parallel and buy 2 of those.

Correct

wdwtx2.0 · Jul 19, 2023

Late to the discussion, but Tim is correct.
In America, you will either see 3 phase, or single phase.
If you look at your POCO power line , you will likely see one hot wire, and one neutral going to the transformer.
Single phase.

Trying to understand the sub panel and how 120/240v work

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