someone mentioned that to figure the grid AC input on the Growatt (24V) 3000TL LVM, you had to take the 3000W inverter load PLUS any AC load being run
Can someone elaborate or correct me on this?
Not quite right, but you are on the right track. The inverter will draw current for the internal battery charger. Therefore, to understand the current on the grid side, you need to consider the external load (i.e. the refrigerator) and the inverter's battery charger load.
So, if the battery charge current is set to 40a on a 24V system, then the battery will be using up to 40A x 28.8V = 1152W. Let's assume the charger is 95% efficient. That would mean the AC needs to supply 1152W/.95=1213W for battery charging. That translates to 1213W/120V=10.1A from the AC for the battery charging.
(Note that if the battery is low, the battery voltage will be lower so the charge wattage will be lower. That means if the battery has a low SOC, the draw on the AC line will be less than a nearly fully charged battery. It is kinda counter-intuitive but true. )
The 1200W of AC load needs a similar calculation. However, it is pass-through so it is 100% efficient. For the 1200W load, the AC current will be 1200W/120V=10A
The total Amps on the grid side will then be 10.1A + 10A = 20.1A
However, if you have 3000W of load (The max for the Growatt), it would be 3000/120=25A for the load for a total of 25A + 10.1A = 35.6A
The good news is that you can adjust the battery charging current in order to better manage the total current on the grid side.
