Growatt split phase issue with 4 units I think resolved but not sure why

[steviep19]

I started upgrading my hardware, and switched over to Growatt recently.

I started with 2 x SPF 3000TL LVM048-P from Signature Solar. At first I put them in Single Phase Parallel, for 6000 watts at 120v and they worked great. I was extremly happy with Signature Solar's email & phone support. They were able to help me and were very nice and experienced.

Although happy with my setup, in the summer I often have extra power with a full battery, and I"m limited to 1.8 kw charging my EV, i switched the config to split phase as a test. The test went perfect, and I was really happy with the results, but I knew I'd need more capacity, as 3000 watt's on each load was just too low, especially with inductive loads, like Air Conditioners, so I purchased two more.

My setup is a little weird. I moved all the 120v circuits from the grid panel, into a Critical loads panel, that's powered by the growatts. I also have a second sub-panel with circuit's I've added. All 120v. 4 x 20amp for the kitchen, 3 x 120v for mini splits (1 ton units, 12000 BTU's they work great), and 120v hot water heating element.

They came in fast like normal and I installed them yesterday, putting two on phase 1 and two on phase 2. This is when I noticed flickering lights. Not all, but most of my LED lights were flickering, sometimes rapidly like a constant pulse. At other times they would flicker almost as if a large inductive load was starting, but there was none.

I read online, to make sure you don't have any ground loops, and I did. One circuit on my house was making contact with ground. Luckily I don't really need it, so I disconnected it thought I solved my problem, but it did not..

I then read in the manual that the Inverters had to have equal cable gauge and length, which I did. It also mentioned attaching all the cables together. I have them all attached to a buss-bar, but I went ahead and put all 4 inverters on the same lug of the bus-bar as a test, this did not work either. All the circuits I have are 120v, so I put both hot legs of the 10-3 wire into the same side of the breaker, this did not resolve the problem either trying both legs one at a time.. Really annoying pulse or constant flicker.

I then saw something about parallel conductors possibly causing issues, It didn't specifically mention sub-panels, and this issue was not present when in utility bypass mode, so I didn't think it would work but I was despite, so I gave it a try. As a test i wired in a 20 amp 120v breaker from the second sub-panel feeding the first, no longer using the direct connection from the Growatts. Much to my shock that worked. No more pulsing, and almost no flickering. only when an AC's compressor starts, which happened before.

Tomorrow, I plan to wire in the 30 amp dual pole breaker and get the subpanel, or should I say sub-sub-panel back to full operation. I'll also have to up the feeder wire to the sub-sub-panel to a larger circuit now that it's powering the additional load.

My questions are. What was the underlying issue causing the pulsing? and Why did this work? This seems to be a fairly common issue with off grid inverters, and it makes no sense to me

 

[ChrisG]

So you had the output of the Growatt feeding both panels directly in parallel , not ‘daisy chained’ together? Trying to understand how the 2nd panel received power in your original config.

 

[DIYrich]

I have them all attached to a buss-bar, but I went ahead and put all 4 inverters on the same lug of the bus-bar as a test, this did not work either. All the circuits I have are 120v, so I put both hot legs of the 10-3 wire into the same side of the breaker, this did not resolve the problem either trying both legs one at a time

You can't do this with split phase. There is 240v between the two different lines. Lucky you didn't fry the inverters.
A diagram of your setup would be helpful.

 

[Quattrohead]

If you think about these power inverters as either a radio transmitter amplifier or an audio amplifier you would then understand that the load is very critical. Yes basically these things are a 50 or 60 hertz amplifier and they can be fussy about their load / antenna/speaker.
So things like impedance, resistance, length of line, imbalance of load etc can all cause slightly weird and wonderful things to happen.
I don't think there's too much understanding of how a home can be a weird load because the utility grid really doesn't give a damn because it is so beefy and robust but obviously trying to use power electronics to drive these loads introduces a whole bunch of variables and unfortunately LED bulbs love to show you these variables.

 

[steviep19]

So you had the output of the Growatt feeding both panels directly in parallel , not ‘daisy chained’ together? Trying to understand how the 2nd panel received power in your original config.

ChrisG,

I'll write up a power flow diagram, but yes.

All four Growatts dumped power into a panel. 2 on each phase. I then had 2x 240 breakers, one into panel a and one into panel b. this is where i had the issue, but when i changed it to feed only panel a, then fed panel b from panel a the issue went away.

 

[steviep19]

You can't do this with split phase. There is 240v between the two different lines. Lucky you didn't fry the inverters.
A diagram of your setup would be helpful.

Sorry wan't clear. When I said I connected them tot he same lug, I mean the Positive & Negative terminals on the DC side instead of different positions on the bus bar, not AC side,

 

[steviep19]

If you think about these power inverters as either a radio transmitter amplifier or an audio amplifier you would then understand that the load is very critical. Yes basically these things are a 50 or 60 hertz amplifier and they can be fussy about their load / antenna/speaker.
So things like impedance, resistance, length of line, imbalance of load etc can all cause slightly weird and wonderful things to happen.
I don't think there's too much understanding of how a home can be a weird load because the utility grid really doesn't give a damn because it is so beefy and robust but obviously trying to use power electronics to drive these loads introduces a whole bunch of variables and unfortunately LED bulbs love to show you these variables.

Does phase imbalance cause issues with these inverters? Judging on my measurements, I do need to balance the loads better between phases.

 

[steviep19]

I actually didn't fix it. I accidentally masked the problem.

It seems like no matter what phase it's connected to, if something else is using power on that phase, I see the flickering. This flicker looks almost to be like the type of flicker you would see when a large load starts up. I'm wondering if the Growatts aren't current sharing properly in that phase.

I had planned to run 6awg from a 60 amp breaker to the load center. I'd say, maybe there's something wrong with my cabling, but this worked just fine with only two units, and when I pass through to the grid, I have no issues as well.

 

[steviep19]

Ok more progress made, and I think this time It's the fix.

The one thing that's not changed in this whole setup was the breaker position. I moved all the growatt breakers next to each-other, and that looks to have solved the issue. I was racking my brain trying to think why this wasn't working with 4 inverters, but was with 2, and with only two load sharing doesn't come into the equation.

Before due to having two dual-pole breakers in the panel, I had to split up the inverter's breaker position. I didn't take a picture but it was something like

---Growatt Phase A---
---30 amp breaker phase A---
---30 amp breaker phase B---
---Growatt Phase B---
---Growatt Phase A---
---40 amp breaker phase A---
---40 amp breaker phase B---
---Growatt Phase B---


Now it's

---Growatt Phase A---
---Growatt Phase A---
---Growatt Phase B---
---Growatt Phase B---
--- Empty ---
---30 amp breaker phase A---
---30 amp breaker phase B---
--- Empty ---

And I"m getting much better results. Some light flickering when large loads start, but that's to be expected.

I think this explains why I didn't see it on utility as well. I think to keep the Growatts in balance the breakers have to be right next to eachother. I think the voltage drop from the loads caused them to over correct.

Does this make sense?

 

[timselectric]

Deleted post

 

[steviep19]

Just a quick update. I was incorrect here as well. Still having flickering lights when I try to run split phase with two inverters in each leg. I think it wasn't flickering, when I first posted it, because nothing else was running on that phase. Once I started adding other loads it came back.

As a test, I paralleled all 4 into 1 phase of 120v 12kw, and everything worked perfect. The problem appears to only be when putting the inverters in split phase with two inverters in each leg.

Until I can figure it out, I've, split out my loads into two seperate subpanels, both fed by one set of Growatts. As a workaround this is working great. No light's flickering, no voltage fluctuation. The only issue is now I essenially have 4 legs at 3000 watts instead of two at 6000 which I was hoping for. I have emailed signature solar, and they've been great so far with assistance

 

[DIYrich]

Maybe add an autotransformer to stabilize the split phase.

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I have 2 Growatt auto transformers for sale one has the hinged door and the other is the later model with the removable lower cover. both are new never used in original boxes, I will take 125.oo each plus shipping I am located in Massachusetts zip code 02771.

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