EG4-6000EX output transformer - how much of a concern?

[Bridgetown]

Hello,

I'm new to the forum, looking to implement an essential circuits backup system within my home.
My system is not built or purchase yet, but I want to get a reality check.

My power usage is currently being monitored and determined by a product from Emporia energy called "Vue". Emporia Energy - Vue
This product seems to be working reliably and was implemented by placing 16 current transformers "doughnuts" on circuits within my home's main service panel. Followed up by reviewing your power consumption on their app which works over Wifi on PC or phone.

My proposed system (so far):

• EG4-6000 inverter
• x2 Server Batteries & rack
• 4800watts of panels
• Reliance ProTran2 transfer switch R310C (10 essential circuits)
• Generator with 48V charge to recharge batteries (maybe EG4 Chargeverter)

What I looked at:
1) Eco-Flow Delta Pros - My first impression was its a nice package, portable, power electronics seemed robust and a little expense.
My main concerns are driven from wanting to implement a smooth operating UPS system.

• Eco-Flow Delta Pros do not allow charging from its 120v AC input power when the Dual Voltage Hub was enabled.
• Pass-thru current was limited to the 120v application (non-Hub) and the current was stated at 18amps (this is what I understand, not much information on the 240V operations)

Otherwise, it seems like a good product for 120v applications. I just felt their 240V implementation needs some attention.

2) BLUETTI AC500 + B300S Home Battery Backup - Again nice packaging, good app. The cost of a second unit to make 240v got too expense for me to continue.

So...back to my system.

With my focus on acquiring an All-in-one EG4-6000EX low frequency inverter which contains a transformer to provide split phase @ 120v/240v output.
I found myself drawn to two new concerns that I have searched the forum community for help;

• Neutral / Ground Bonding - My initial concern was simply try to understand the enormous discussions surrounding internal screws, stationary & mobile applications. An it appears now with, vendor Signature Solar's commitment to the February firmware of common neutrals and "no screws" that our forum leaders (Filterguy, Hedge, Timelectric, RCinFLA) have managed to document and sort out various implementations to help remove ambiguity surrounding the topic. Many thanks for your efforts, your work in this subject area is appreciated. Your dedication to properly document is situations where manufactures do not share their schematics is a great value to someone who is new and trying to build their first system!
• Common neutrals when using an low frequency all-in-one inverter with a transformer - Some concerned still exists with paralleling transformers

I believe in my case, the output of the EG4-6000EX invert's autotransformer will be put in parallel to the grid's transformer coming into the house (during pass-thru operation). The neutrals and hot legs of both grid and inverter transformers will be connected in parallel within my system (based on information that I have been discovering).

This most likely means, neutral current from my inverts autotransformer on ground wire will be caused by any imbalance in grid L1-N and L2-N as the result of autotransformer trying to correct any grid 120vac phase imbalance.

At this time, I not sure to what degree this is a problem. I already know that I will not be able to balance my loads perfectly much less being concerned about balancing my grid's transformer (assuming neighbors are connected). So I will need to do my best when I balance my homes loads. But what about the grid imbalance?

Looking for some feedback:

a) How much of my EG4-6000EX inverters (transformer) output capacity will be utilized trying to balance my grid transformer? Is there a way to measure or do I just have to hook it up and measure? Is this a typical concern that is dealt with somehow? Trying yo understand.

b) Are there other ways to help mitigate this situation?

 

[Bridgetown]

Any comments or past experience you can share?

 

[RCinFLA]

There are two primary concerns when using an autotransformer.

First is overloading transformer. Auto transformer load is 120vac load phase imbalance. If you have 20 amps on one 120vac phase and 5 amps on other phase the transformer is providing 15 amps to balance the 240vac AC input current.

Minimally, you should have a temp sensor on transformer that will shut off 240vac source to be safe.

Second is neutral-ground bonding when connected to grid. If grid L1-N and L2-N is imbalanced, an autotransformer with neutral-ground bonding will try to correct the grid imbalance. This eats up transformer capacity and may cause it to overheat. This is why you should have temp sensor 240vac shutdown to autotransformer even if you assure your 120vac load imbalance cannot exceed transformer rating.

To make things more confusing, many manufacturers of autotransformers for DIY'er rate their transformer for twice the actual transformer rating. The typical '5 kVA' autotransformer will get over 200 degs F in about 25-30 minutes if a sustained 5 kVA 120vac load imbalance is placed on transformer. They are really 2.5 kVA continuous rating autotransformer so a 5 kVA inverter can cause them to be overloaded.

A transformer can be 2x rating overloaded for a short period of time without getting too hot.

 

[Hedges]

With my focus on acquiring an All-in-one EG4-6000EX low frequency inverter which contains a transformer to provide split phase @ 120v/240v output.
...
I believe in my case, the output of the EG4-6000EX invert's autotransformer will be put in parallel to the grid's transformer coming into the house (during pass-thru operation). The neutrals and hot legs of both grid and inverter transformers will be connected in parallel within my system (based on information that I have been discovering).

This most likely means, neutral current from my inverts autotransformer on ground wire will be caused by any imbalance in grid L1-N and L2-N as the result of autotransformer trying to correct any grid 120vac phase imbalance.

At this time, I not sure to what degree this is a problem. I already know that I will not be able to balance my loads perfectly much less being concerned about balancing my grid's transformer (assuming neighbors are connected). So I will need to do my best when I balance my homes loads. But what about the grid imbalance?

Looking for some feedback:

a) How much of my EG4-6000EX inverters (transformer) output capacity will be utilized trying to balance my grid transformer? Is there a way to measure or do I just have to hook it up and measure? Is this a typical concern that is dealt with somehow? Trying yo understand.

Does it have auto-transformer?
I found the following manual, which describes 120V (single phase) inverter:

https://eg4electronics.com/wp-content/uploads/2022/10/EG4-6500EX-48-Manual.pdf

If yours would be a different model, can you provide links?

Stacking 2x 120V inverters for 240V would not have auto-transformer, and would not have problem of it attempting to balance grid.
You would be limited on each 120V phase to capacity of one inverter.
You could add an auto-transformer, to be connected only when off-grid, which would partially distribute load to both inverters.

With two, you would want to think about two neutral-bonding relays and whether one should be isolated.

Using a single 120V inverter, you could use auto-transformer to generate 120/240V split-phase. No issue with it trying to balance grid. Loads on second phase would be limited to auto-transformer capacity.

 

[RCinFLA]

EG4-6000 inverter is split-phase LF inverter with output transformer. Same issues as a 240vac inverter with autotransformer with regards to grid phase imbalance.

A LF split-phase inverter (Xantrex, Outback) have output transformer neutral current imbalance monitoring. On LF split-phase output transformer, in addition to transformer heating, which has a long time response lag, any grid imbalance can limit the available output transformer capacity to the actual inverter. This can cause transformer saturation causing output MOSFET's of inverter to blow out, if there is no monitoring for grid neutral current imbalance. Since this inverter cannot load shave, the transformer saturation situation would only happen for large charging current demand.

 

[Hedges]

Can you provide a link to EG4-6000?
I'm finding EX, EHV, etc.

You say that one is split phase with transformer.

Post title says eg4-6000ex; I found links indicating 120V single phase.
But body of post #1 says EG4-6000. Hey OP @Bridgetown, which model is it?

I think built-in auto-transformer could work without problems on/off grid if disconnected when on grid. Don't know if this manufacturer did that, or tested it once and thought OK always connected.
And, if not sufficiently large, monitored for overload as you say.

"transformer saturation causing output MOSFET's of inverter to blow out"
Would that be one and the same situation as having a load which is short circuit?
At least with saturated transformer, there is winding resistance. Shorted output or H-bridge improperly enabled would just be couple of FETs across the power supply (for a LF design).

But what about buck topology, which I think is part of HF inverter design, likely also LF sine-wave design. Does that inductor limit fault current? And HF, only capacitors behind it, no battery.

 

[Bridgetown]

Post title says eg4-6000ex; I found links indicating 120V single phase.
But body of post #1 says EG4-6000. Hey OP @Bridgetown, which model is it?

EG4-6000EX-48HU

EG4-6000EX-48HU Split Phase output link

 

[Hedges]

"Output Voltage Waveform Pure Sine Wave (>3% THD)"

"Grid-Tie operation - Nominal Output Current 27.3A (for 110VAC) 25A (for 120VAC)"

I'm not able to tell from specs section how much power it can deliver on just one 120V leg. Maybe transformer supports 3kW continuous, maybe even more. Or not.

I haven't found mention of bonding.
Can't tell if it does put auto-transformer across grid L1/N/L2.

 

[Bridgetown]

This eats up transformer capacity and may cause it to overheat.

Thanks for response, it really helps to known prior to purchasing.

I'll follow up on your suggestion of manufacturers who monitor the "imbalanced current" in the neutral (Xantrex, Outback).

So...I'm curious...since I have not purchased yet. Do the manufacturers of other low frequency inverters (Schneider, Victron) with their toroidal output transformers get around this problem?

 

[Hedges]

I think Schneider switches auto-transformer depending on whether grid is connected.
Sunny Island is 120V, so two are stacked for split-phase and no auto-transformer is used.
Sunny Boy storage is high frequency, and auto-transformer & transfer switch are in an external box.

Victron's Autotransformer monitors center tap current (28A max continuous) and temperature, shutting off 100A L1/L2 breaker if overloaded.
Victron has dynamic neutral/ground bonding, but does NOT connect center tap back to grid. I think that is incorrect, not NEC compliant, for US market. I would consider rewiring it to connect centertap to neutral, and hardwire neutral to grid.

 

[Bridgetown]

I think Schneider switches auto-transformer depending on whether grid is connected.
Sunny Island is 120V, so two are stacked for split-phase and no auto-transformer is used.
Sunny Boy storage is high frequency, and auto-transformer & transfer switch are in an external box.

Victron's Autotransformer monitors center tap current (28A max continuous) and temperature, shutting off 100A L1/L2 breaker if overloaded.
Victron has dynamic neutral/ground bonding, but does NOT connect center tap back to grid. I think that is incorrect, not NEC compliant, for US market. I would consider rewiring it to connect center tap to neutral, and hardwire neutral to grid.

Thanks! good to know. And yes! I would like to implement the common neutrals to stay NEC compliant.

This brings me back to my initial concerns which may be tough to answer up front.

 

[Bridgetown]

...

So.... a stretch question, looking to your experience, maybe cannot be answered (to be fair).

How much neutral imbalance current can one expect from their home's service entrance grid? With the thought of adding a low frequency inverter containing a transformer?

Let's assuming I can keep my loads in relative balanced, lets say L1 & L2 within 0-6amps.

Is there a way to measure or do I just have to hook it up and measure?

Otherwise, the low cost, low frequency inverts like the EG4 6000EX-48EX could be risk to purchase, especially if they do not monitor the temperature of the transformer which my be too lagging of an indicator to prevent harm (per RCinFLA point).

 

[Hedges]

Whatever your loads are is probably OK, although I wish EG manual was explicit about allowed imbalance.
The farther it is from grid, the less your autotransformer will try to rebalance. Worst case outcome ought to be equipment shutting off, although I can't know EG protects itself.

6kW split-phase inverter for $1300? If only the inverter itself is at risk, not a high cost to gamble. Fire safety would be another matter.

Is it UL listed? I see no mention. "Off grid", "Grid Backfeed Rated for Non-US International use"

So I can't say for sure how appropriate it is to connect to our grid.
Will it work with just 120V input? If so, that might keep your battery charged and avoid issues with auto-transformer. But that requires inverter to synchronize to grid to make missing phase. My SI do that, don't know for sure about this one.

 

[RCinFLA]

How much neutral imbalance current can one expect from their home's service entrance grid? With the thought of adding a low frequency inverter containing a transformer?

Imbalance is usually caused by you or your neighbors 120vac loads and how many of your neighbors share the same pole transformer. It is worse when you have a single branch extension line from pole transformer (usually large lots) where there is a second pole to split the long 240/120v feed to you and your neighbor.

I have an acre lot with the split 240/120vac feed with my neighbor. About a 130' common feed from pole transformer that splits into two 120' branches to each house. I typically see 2 to 5 amps of imbalance.

A really bad situation is if you have a poor utility feed line neutral connection. The bare support cable that the L1 & L2 lines are wrapped around is the neutral connection. This cable also provides the mechanical line support so it is subjected to stress from storms. The support neutral cable is a smaller gauge bare steel cable.

There are conditions that make things worse, like you or your neighbors with a large air compressor or water pump that is wired for 120vac operation.

99+% of the time there is no issue, but when and if there is, (like a bad utility neutral connection) the inverter must recognize it and release from grid to prevent damage to inverter.

Most LF inverter that have load shaving feature will also be checking for utility neutral imbalance. Both require AC input current sensors in addition to current sensor on actual inverter stage.

 

[RCinFLA]

Any low frequency inverter that does split-phase 240/120vac output with a single output transformer/inverter acts like an autotransformer when in AC pass-through.

There is no so such thing as separate grounds. Separate ground stake on subpanel will not solve the grid neutral imbalance issue. Neutral-ground bond in main panel, and neutral-ground bond on inverter output subpanel also means grid neutral is connected to subpanel neutral via the common ground connection. Two separate ground stakes just means the neutral imbalance current flows through the earth between the stakes.

 

[Hedges]

Easy fix, though.
Buy a used isolation transformer. Feed it with 240V from grid, derive an isolated 120/240V split-phase to feed your property (and bond the new neutral to ground.)

I think you could get away with doing that just to feed inverter & protected loads panel, but also feed whole house when desired. In that case you would want transfer switch to switch neutral as well.

 

[RCinFLA]

Easy fix, though.
Buy a used isolation transformer. Feed it with 240V from grid, derive an isolated 120/240V split-phase to feed your property (and bond the new neutral to ground.)

I think you could get away with doing that just to feed inverter & protected loads panel, but also feed whole house when desired. In that case you would want transfer switch to switch neutral as well.

Nope, utility pole neutral is grounded. No such thing as separate grounds, only separate grounds with variable amount of resistance between them.

Throw in a cable TV or telephone line going to utility pole and you have a dangerous situation.

Utilities do not rely on isolation transformers to take lightning hits. All primary and secondary sides of utility transformers have ground connections.

 

[Hedges]

I wasn't saying separate ground.
But I've improved on my idea.

Revision:

Derive an isolated L1/N/L2 with isolation transformer. Connect its neutral to neutral of your main panel, which provides N/G bond. Feed L1/N/L2 to inverter with internal auto-transformer.

Now, your protected loads panel has its auto-transformer and doesn't try to rebalance grid (only your own split-phase transformer).
You can also throw a 2-pole interlocked breaker to backfeed main panel when desired (no need to switch neutral).

 

[Bridgetown]

@RCinFLA
Thanks for keeping me focused on my potential 120V load imbalances since my 240v loads do not contribute to this imbalance.

There are conditions that make things worse, like you or your neighbors with a large air compressor or water pump that is wired for 120vac operation.

I feel, it is this uncertainty that I'm trying to assess.

Living in a suburban neighborhood with two other neighbors sharing an underground transformer in my front yard. Allows me to understand my environment for potential imbalances. No well pumps or small machine shops amongst my neighbors.

Revision:

Derive an isolated L1/N/L2 with isolation transformer. Connect its neutral to neutral of your main panel, which provides N/G bond. Feed L1/N/L2 to inverter with internal auto-transformer.

Okay...thanks giving me ideas for potential solutions!

 

[42OhmsPA]

"Output Voltage Waveform Pure Sine Wave (>3% THD)"

"Grid-Tie operation - Nominal Output Current 27.3A (for 110VAC) 25A (for 120VAC)"

I'm not able to tell from specs section how much power it can deliver on just one 120V leg. Maybe transformer supports 3kW continuous, maybe even more. Or not.

I haven't found mention of bonding.
Can't tell if it does put auto-transformer across grid L1/N/L2.

I've had my TP6048 up to 2.5kw on one leg, ~700w on the other with no issues, using a space heater and induction cooktop.
It's my understanding that 3kw per leg is the continuous output on these with a 10s surge twice that.
I know it handles my well pump surge (clamped at ~36a per leg with no issues) I also know idle consumption is terrible.