3 phase to a 2 Phase Eg4 18kpv Inverter

[timselectric]

That's what I've been worried about (for the OP).

They aren't using the third leg for input or output.
And no loads are shared with it.
So, as far as the 18kpv goes, it doesn't exist.

 

[ksmithaz1]

If he has a 220V load on L2 and L3, and L2 goes through the 18kPV but L3 doesn't, and the grid drops out, the inverter will only be powering L2 and N. What will will happen?

And aren't L1 and L2 only 120 degrees apart? Shouldn't the 18kPV be told that?

Since they have wiring diagrams for 2 or 3 units in a 3 phase arrangement, I'm guessing that should not really be problematic, but it's a point well explored. The problem as I see it is you're going to end up overloading one phase, kind of defeats the purpose, draw all your juice from L1-L2, the other two have nothing. Might attract attention from the power company as well when you are in bypass.

 

[ksmithaz1]

If the feed is 50A per leg x 120V x 3 legs = 18,000W
18,000W / 208V / 3 legs = 28.8A, not 50A

Two 208V loads are pulling on one 50A 120V phase, but each at a 60 degree angle.
28.8A x sin(60) x 2 = 50A
Of course if the two 208V loads are not equal, the net draw is out of phase current.
The inverters may be able to deliver more than 28.8A to a single 208V load, maybe even 50A. In which case two inverters are each delivering 6kVA but only 3kW. Their internal power dissipation probably approaches what it would have been for 6kW, lower efficiency.

I think you're correct it "limits each to 50A", just can't support all three at once 50A. Assuming the inverter is happy with reactive loads.

Man, you really are trying to make me look all this sh*t back up aren't you? It get's really fuzzy after 40+ years. @timselectric works with this stuff every day, I'm sure he can confirm one way or the other, but I'm pretty sure when it comes to the 208, you can pull 50A from each leg, subject to the normal 80% rules. Looking into some lower end DCFC installs, they generally spec 208/50A or 240/150A service to support a 25KW unit. Since Neutral is bound to each leg, your saying you only get 2/3 of the potential because it's shared, and not 180 degrees out from only one? So 120v is different? As we head into the weeds, ...

 

[Supervstech]

Man, you really are trying to make me look all this sh*t back up aren't you? It get's really fuzzy after 40+ years. @timselectric works with this stuff every day, I'm sure he can confirm one way or the other, but I'm pretty sure when it comes to the 208, you can pull 50A from each leg, subject to the normal 80% rules. Looking into some lower end DCFC installs, they generally spec 208/50A or 240/150A service to support a 25KW unit. Since Neutral is bound to each leg, your saying you only get 2/3 of the potential because it's shared, and not 180 degrees out from only one? So 120v is different? As we head into the weeds, ...

He misunderstood the situation, inverter ONLY outputs single phase on two legs of the panel, so, 50A each 120V leg, or 50A across L1L2 combined...
Only get out around 10,800W at 216V

 

[ksmithaz1]

I still say running against only one phase is going to cause issues eventually. Every time *I* do dumb sh*t like this it *always* ends up biting me in the rump at the worst possible time, and whatever I need to make it work is only available at the Lowes/Home Depot 1/2 way across town. YMMV.

The 18KPV seems to support a full 3P with only two inverters, I really don't grok what they are doing to make the magic work for the 3rd phase, be that as it may, $5K seems like cheap insurance, to get something to a fully supported configuration all the way around.

 

[timselectric]

There's nothing wrong with having backup on only part of a service.
I'm almost positive that the only thing that is 3-phase on the property is the service. All loads are most likely single phase. Either 120v or 208v (126/218).
And for clarity on the other conversation. A 50a service will provide 50a on any single leg, or combination of legs.

 

[Hedges]

A split-phase inverter with two independent 120V inverters can just have a timing signal to make them 120 degrees apart, or 180 degrees apart.
Then two such inverters could provide 3-phase and have a spare leg left over. Likely doubles up current on one leg. I'd rather have it in phase (or 180 degrees out of phase if your name isn't Tim), wired so the four legs are good for both 120/208Y and 120/240V split-phase. The split phase would be good for split-phase grid or generator input.

 

[billvon]

There's no such thing as 2 phase.

Well, there is, but no one works with that much.

However, two of three phases plus a neutral is very close to what 2 phase is, which is two feeds 90 degrees out of phase with each other. 2 phases (plus neutral) of a 3 phase feed are only 60 degrees out of phase, but they will still do all the things that a "true" 2 phase feed will do (i.e. run induction motors without starting capacitors.)

 

[zanydroid]

Does the phase angle make a difference to the individual inverters creating the Y legs? I guess it might affect the ratio between the kVAs induced into the inverters and the kW sent to the loads.

 

[timselectric]

Well, there is, but no one works with that much.

However, two of three phases plus a neutral is very close to what 2 phase is, which is two feeds 90 degrees out of phase with each other. 2 phases (plus neutral) of a 3 phase feed are only 60 degrees out of phase, but they will still do all the things that a "true" 2 phase feed will do (i.e. run induction motors without starting capacitors.)

Not quite.
Yes 2 phase did exist (and still does in a couple locations). But they were independent of each other. As in two sets of two conductors. (No shared conductors) which is why it was mostly abandoned when 3-phase replaced it.
Two legs of 3-phase (with or without a neutral) is just one (single) phase of the 3. The 3 phases are 120° of timing from each other. You are confusing legs (conductors) with phases.
I explained this in post #56 of this thread.