Load sharing between 2 inverters in split phase config.

[agentdiysolar]

So i have 2x EG4 3000EHV-48, wired in a split phase (220v [L1-110v/N/L2-110v]) config into an Critical loads panel. Was sized based on what i use and typical loads stay around 1.8-2kw , but have peaks that go to 4.5. All works well (mostly). I have found that one of the inverters always has a higher load (at 975-1000w ) despite my attempts to move circuits on the panel to try to balance them. and when we run our toaster oven one inverter spikes to 3k (and a couple time has gone into overload mode) . What can i do to balance the loads between them ? thought of an auto transformer but not sure if it would work let alone what the wiring scheme would look like.

any suggestion or ideas ? short of going a bigger (or single split phase inverter). as never does our peak load go above 4500W (yet).

 

[timselectric]

So i have 2x EG4 3000EHV-48, wired in a split phase (220v [L1-110v/N/L2-110v]) config into an Critical loads panel. Was sized based on what i use and typical loads stay around 1.8-2kw , but have peaks that go to 4.5. All works well (mostly). I have found that one of the inverters always has a higher load (at 975-1000w ) despite my attempts to move circuits on the panel to try to balance them. and when we run our toaster oven one inverter spikes to 3k (and a couple time has gone into overload mode) . What can i do to balance the loads between them ? thought of an auto transformer but not sure if it would work let alone what the wiring scheme would look like.

any suggestion or ideas ? short of going a bigger (or single split phase inverter). as never does our peak load go above 4500W (yet).

This is why I'm not a fan of putting inverters in series for split-phase.
Yes, an autotransformer will solve the problem if you don't have grid input to the AIO's. If you do, then I would recommend an isolation transformer.
Basically in either case. You use the inverters to create 240v only. (Don't use the inverter neutrals)
And let the transformer create the split-phase.
If able to use the autotransformer, make sure to double the size of the neutral.

 

[agentdiysolar]

This is why I'm not a fan of putting inverters in series for split-phase.
Yes, an autotransformer will solve the problem if you don't have grid input to the AIO's. If you do, then I would recommend an isolation transformer.
Basically in either case. You use the inverters to create 240v only. (Don't use the inverter neutrals)
And let the transformer create the split-phase.
If able to use the autotransformer, make sure to double the size of the neutral.

I do have grid input (split phase between the inverters - each on a 110V leg) ) . AIOs are setup in SBU mode with switch to Utility set at 30% battery ( to be offgrid as much as possible yet have backup) . So isolation transformer seems to be what i need -right ?. Is not using the neutrals of the AIO, they just remain - unconnected ?

 

[timselectric]

So isolation transformer seems to be what i need -right ?.

Yes

Is not using the neutrals of the AIO, they just remain - unconnected ?

Yes
You just want the inverters to provide 240v to the transformer. This way all balanced and unbalanced loads will be equally balanced through the AIO's.

 

[ChrisG]

Yes

Yes
You just want the inverters to provide 240v to the transformer. This way all balanced and unbalanced loads will be equally balanced through the AIO's.

@timselectric
Do you have an example of one to use/buy. Was looking at the Victron 3600 isolation transformer but not clear how the US neutral is derived from documentation.

 

[timselectric]

You can find used transformers on Ebay for reasonable prices. They almost never fail. They usually get removed during store remodeling.
I wasn't aware that Victron sold an isolation transformer. I do know that they sell an autotransformer.

 

[timselectric]

As far as hooking it up.
There's usually a diagram on the front cover.
Otherwise, I or someone else here can walk you through it.

 

[EastTexCowboy]

This is why I'm not a fan of putting inverters in series for split-phase.
Yes, an autotransformer will solve the problem if you don't have grid input to the AIO's. If you do, then I would recommend an isolation transformer.
Basically in either case. You use the inverters to create 240v only. (Don't use the inverter neutrals)
And let the transformer create the split-phase.
If able to use the autotransformer, make sure to double the size of the neutral.

This is probably my biggest regret on going with the LV6548. It hasn't been a problem as of yet but when I start pushing the upper limits I'm afraid it could become one. Live and learn, I reckon. I've already been thinking about upgrading these inverters then maybe using these in the shop or something. Or I could do the isolation transformer but I'm already running out of wall space.

@ OP - It sounds like Tim's suggestion might make the most sense and should eliminate the problem. Or you could weigh the cost of the isolation transformer against upgrading to a single inverter with split phase output. You could likely recover some of the cost by selling your current inverters. You could list them for sale here on the forum.

 

[ChrisG]

You can find used transformers on Ebay for reasonable prices. They almost never fail. They usually get removed during store remodeling.
I wasn't aware that Victron sold an isolation transformer. I do know that they sell an autotransformer.

Here is the one I mentioned above. Not sure the Victron works as you mentioned above: https://www.victronenergy.com/uploa...Auto/108939-Isolation_transformers-pdf-en.pdf

I assume your talking about one like this and you’re right, they are all over eBay: https://www.ebay.com/itm/3838823988...624&ssuid=&var=&widget_ver=artemis&media=COPY

 

[timselectric]

Here is the one I mentioned above. Not sure the Victron works as you mentioned above: https://www.victronenergy.com/uploa...Auto/108939-Isolation_transformers-pdf-en.pdf

That's a different type of isolation.
You need one to create split-phase.

I assume your talking about one like this and you’re right, they are all over eBay: https://www.ebay.com/itm/3838823988...624&ssuid=&var=&widget_ver=artemis&media=COPY

Yup

 

[timselectric]

This is probably my biggest regret on going with the LV6548. It hasn't been a problem as of yet but when I start pushing the upper limits I'm afraid it could become one. Live and learn, I reckon. I've already been thinking about upgrading these inverters then maybe using these in the shop or something. Or I could do the isolation transformer but I'm already running out of wall space.

@ OP - It sounds like Tim's suggestion might make the most sense and should eliminate the problem. Or you could weigh the cost of the isolation transformer against upgrading to a single inverter with split phase output. You could likely recover some of the cost by selling your current inverters. You could list them for sale here on the forum.

Just keep in mind that a high frequency split-phase inverter is just two inverters in series, in a single enclosure.
Low frequency (with built-in transformer) will have a balanced inverter. And full rated output.

 

[EastTexCowboy]

Just keep in mind that a high frequency split-phase inverter is just two inverters in series, in a single enclosure.
Low frequency (with built-in transformer) will have a balanced inverter. And full rated output.

I learn something every day here. I've been looking at the Growatt 12kw low freq thinking I may could stack two of them and get everything I need. Or maybe something from Victron and just bite the bullet on cost. But that's for another thread if and when I get closer to actually making a change, rather than hijacking this thread. This is part of why you went with the SPF5000 inverters, I'm guessing.

 

[TomC4306]

I don't quite see WHAT problem you are trying to fix. You are never going to perfectly balance consumption on the two phases. There is always going to be an imbalance. Yes, minimize it but you won't eliminate it.
This was exactly the reason I DID use separate inverters for split phase. Because it just doesn't matter. My imbalance can be 2000 w but what does it matter if one inverter is providing 2500 watts to L1 and the other inverter is only providing 800 watts to L2 at any given moment?
If I were on grid the same imbalance in my house would prevail.

 

[EastTexCowboy]

I don't quite see WHAT problem you are trying to fix. You are never going to perfectly balance consumption on the two phases. There is always going to be an imbalance. Yes, minimize it but you won't eliminate it.
This was exactly the reason I DID use separate inverters for split phase. Because it just doesn't matter. My imbalance can be 2000 w but what does it matter if one inverter is providing 2500 watts to L1 and the other inverter is only providing 800 watts to L2 at any given moment?
If I were on grid the same imbalance in my house would prevail.

I think what he's trying to fix is one leg is maxing out and tripping the overload while the other leg has minimal load. If the max load the inverter will support is 3000w and one leg exceeds that then the inverter supplying that leg is going to overload. It doesn't work that way with an imbalance on the grid, although if you exceed the maximum load on one leg of a double pole breaker, including the main breaker, the breaker should trip. Based on my education from @timselectric, I believe the transformer supplying your home balances the load otherwise.

 

[TomC4306]

I too have pair of 3K inverters. Whenever one of mine sees a peak in excess of its capacity, I see a bit of grid assist for the duration of the peak. Nothing goes into overload and nothing trips.
My normal base load though is lower than his.
We are careful not to try and make heat on more than one device simultaneously. I e microwave and coffee pot and toaster.

Edit .. if we were unable or unwilling to be careful, that would argue for upgrading the inverters.

 

[timselectric]

I've been looking at the Growatt 12kw low freq thinking I may could stack two of them and get everything I need.

Not stackable.

This is part of why you went with the SPF5000 inverters, I'm guessing.

Yes, I get full capacity whether I am balanced or not.
The inverters see no imbalance.

 

[EastTexCowboy]

Not stackable.

Yeah, I figured that out looking a little more today.

 

[Quattrohead]

This is probably my biggest regret on going with the LV6548. It hasn't been a problem as of yet but when I start pushing the upper limits I'm afraid it could become one.

We just beat on ours tonight, dryer, hwt and ac all hitting them to around 90% load. They got a little loud and were pulling 172A. ?

 

[1201]

I too have pair of 3K inverters. Whenever one of mine sees a peak in excess of its capacity, I see a bit of grid assist for the duration of the peak. Nothing goes into overload and nothing trips.
My normal base load though is lower than his.
We are careful not to try and make heat on more than one device simultaneously. I e microwave and coffee pot and toaster.

Edit .. if we were unable or unwilling to be careful, that would argue for upgrading the inverters.

Which inverters do you use?

 

[EastTexCowboy]

We just beat on ours tonight, dryer, hwt and ac all hitting them to around 90% load. They got a little loud and were pulling 172A. ?

How many inverters are you running?