230vac single phase output to 220v with a center tap transformer

Welcome to the forum MrFCC1.

Is this for use in North America (central California?) or somewhere with 240/220 VAC as line voltage? In North America, the "center tap" of the 120/240 VAC line is a ground referenced neutral. In other 220/240 VAC native countries, one leg of the 2X0 VAC line is usually ground referenced (may vary by country).

Are you going to connect to the utility grid as a hybrid/GT capable inverter? Will this hybrid inverter+charger meet your UL/NEC requirements?

If you are planning on using this system in North America--You probably should get a wiring diagram from EAsun to ensure that the inverter is connected as they expect to the utility.

Transformer wise, you have two major choices... An "auto" transformer that has only one set of windings. You connect L1/L2 to 240 VAC, and the center tap gives you 120/240 VAC output... However the output of such a transformer is NOT isolated from the AC input... So the Neutral bonding of AC neutral/center tap of North America would require you to "float" L1 and L2 to the hybrid inverter.

Here is an example of an Auto-Wound Transformer that is used on off grid AC power systems:

https://www.solar-electric.com/x-240.html

The other major type is a two winding transformer... Isolated from AC In to AC Out of the system... You can have 240 native with ground bonded neutral on the 240 VAC side, and the Neutral Center Tap ground bonding on the 120/240 VAC output of the transformer.

I did not find many details on your inverter+charger... In the US, L1/N/L2 ground bonding must be done "right" or the typical hybrid/GT inverter will fault... I did not see any reference on how this product would behave with L1/L2 floating AC outputs (on a quick read):

http://www.easunpower.com/Products/Off-Grid/5000W_Parallel_Inverter/93.html (yours?)

Transformers add cost and complexity, as well as some additional losses--It does not usually make a lot of sense to try and "converter" a non-North America inverter to a North American grid connection (and it may not be to code either).

-Bill

A friend of mine has been going to (and now online) equipment auctions where he has gotten some very good deals on isolated (two sets of windings) transformers (step up or step down for 120/240/208/480 VAC etc.) from machine shops.

A 5 kVA 120/240 VAC transformer on Amazon is around $1,000.... I am sure you are looking for a less costly option...

I am not in the industry--So I cannot really give you much guidence--But here is a nice catalog about Buck-Boost and AutoWound transformers:

https://hubbellcdn.com/ohwassets/HCI/Acme_Electric/Literature/SECTION-7.pdf
https://www.hubbell.com/acmeelectric/en/Catalog (other transformers)

Perhaps the above link(s) may help... Or you an call them and get some sales help.

There are just so many design issues with Transformers, I just don't want to lead you down the wrong path.

Perhaps some other folks here can help...

-Bill